Sätt chartets platshållarversion till 0.9.2

Kosmetiskt, och görs ändå. .gitea/workflows/release.yaml stämplar både
version och appVersion från git-taggen när det publicerar (766f439), så de
här två raderna avgör ingenting om vad som hamnar i registret. Det enda de
gör är att bli lästa, och de sa 0.9.0 och "latest" genom både v0.9.0 och
v0.9.1 — ett träd på väg mot v0.9.2 som säger 0.9.0 påstår något falskt om
sig självt.

Första gången det görs i det här repot, så det finns inga tidigare
tillfällen att hänvisa till. Kommentaren ovanför raderna skrevs om samtidigt:
den hävdade att "latest" var ärligt eftersom det matchade image.tag i
values.yaml, vilket slutade gälla i och med den här ändringen. image.tag
ligger kvar på "latest", som är vad en lokal installation faktiskt drar;
appVersion är metadata och styr ingenting. Att låta kommentaren stå kvar
hade varit sämre än ingen kommentar alls, eftersom den är det en läsare
kontrollerar fälten mot.

Claude-Session: https://claude.ai/code/session_01S7R4gWTz5wh5xCY4nCSJjN

.gitea/workflows/ci.yaml

@@ -0,0 +1,90 @@
+name: CI
+
+# The release workflow gates a tag, which is late: a broken commit sits green until
+# somebody decides to publish. This runs the same checks on the way in.
+#
+# push is scoped to main rather than all branches so that a branch pushed as part of a
+# pull request is not checked twice.
+#
+# No actions/checkout, deliberately -- same as the letsvisit and charts workflows. The
+# runner image is ubuntu:22.04 whose `nodejs` package is Node 12, and actions/checkout@v4
+# is built with ES2022 static initialiser blocks, so it dies with
+# `SyntaxError: Unexpected token '{'` before running. Cloning with git directly avoids JS
+# actions entirely. This repo is public, so the clone needs no credential at all.
+#
+# `${{ }}` values are passed through `env:` and referenced as quoted shell variables: a
+# ref name is attacker-influenced by anyone who can push a branch or open a PR, and
+# expanding one straight into `run:` is a shell-injection vector.
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+# A rapid series of pushes only needs the last one checked.
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  REPO_URL: https://git.ryuvia.com/niklas/terdut-server.git
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    container:
+      # Runs inside the toolchain image rather than installing Go per job. Note this puts
+      # the job on the dind bridge, which cannot reach github.com or get.helm.sh --
+      # proxy.golang.org and git.ryuvia.com are reachable, which is all this job needs.
+      image: golang:1.26.6-bookworm
+      # act_runner destroys a job's own volumes when it finishes, so without these every
+      # run re-downloads the whole module graph. The names must appear in the runner's
+      # container.valid_volumes allowlist (charts/act-runner in the k8s repo); unlisted
+      # volumes are dropped silently, so a workflow that looks correct can still be
+      # running uncached.
+      volumes:
+        - go-mod-cache:/go/pkg/mod
+        - go-build-cache:/root/.cache/go-build
+        - gobin-cache:/go/bin
+    steps:
+      - name: Checkout
+        env:
+          REF_NAME: ${{ github.ref_name }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          if [ -n "$HEAD_SHA" ]; then
+            # A pull_request ref_name is "<n>/merge", which is not a fetchable branch.
+            git clone "$REPO_URL" .
+            git checkout -q "$HEAD_SHA"
+          else
+            git clone --depth=1 --branch "$REF_NAME" "$REPO_URL" .
+          fi
+
+      # This exists because `go vet` does not look at import order: the move to
+      # git.ryuvia.com rewrote every import path without re-sorting, the new path sorts
+      # before github.com/..., and both repos sat unformatted through a green CI run and
+      # a release before anyone noticed.
+      #
+      # Both of gofmt's failure modes need handling, and they are not alike. A file that
+      # is merely misformatted is listed on stdout with exit 0 -- so the failure has to
+      # be raised by hand. A file that does not parse is the opposite: nothing on stdout
+      # and exit 2, which a naive `[ -n "$unformatted" ]` reads as success. The first
+      # draft of this step had exactly that hole.
+      - name: Format
+        run: |
+          if ! unformatted=$(gofmt -l .); then
+            echo "::error::gofmt could not parse the tree"
+            gofmt -l .    # re-run unredirected so the parse errors reach the log
+            exit 1
+          fi
+          if [ -n "$unformatted" ]; then
+            echo "::error::not gofmt'd:"
+            echo "$unformatted"
+            gofmt -d .
+            exit 1
+          fi
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test ./...

.gitea/workflows/release.yaml

@@ -0,0 +1,235 @@
+name: Release
+
+# Checkout, interpolation and caching conventions match ci.yaml -- see the header there
+# for why there are no JS actions and why every `${{ }}` goes through `env:`.
+#
+# There is no upload-artifact/download-artifact equivalent here (both are JS actions, and
+# this Gitea has no artifact store wired up), so the job that builds the binaries is also
+# the job that publishes them. Nothing is handed between jobs at all.
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+# A tag is not normally re-pushed, so this mostly matters when one is force-moved during
+# a botched release -- the superseded run stops holding runner slots.
+concurrency:
+  group: release-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  REPO_URL: https://git.ryuvia.com/niklas/terdut-server.git
+  API: https://git.ryuvia.com/api/v1/repos/niklas/terdut-server
+  REGISTRY: git.ryuvia.com
+  IMAGE: git.ryuvia.com/niklas/terdut-server
+
+jobs:
+  # Gates every publishing job below. A tag that fails here publishes nothing: the
+  # binaries, the image and the chart are all downstream of it.
+  test:
+    runs-on: ubuntu-latest
+    container:
+      image: golang:1.26.6-bookworm
+      volumes:
+        - go-mod-cache:/go/pkg/mod
+        - go-build-cache:/root/.cache/go-build
+        - gobin-cache:/go/bin
+    steps:
+      - name: Checkout
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: git clone --depth=1 --branch "$REF_NAME" "$REPO_URL" .
+
+      # This exists because `go vet` does not look at import order: the move to
+      # git.ryuvia.com rewrote every import path without re-sorting, the new path sorts
+      # before github.com/..., and both repos sat unformatted through a green CI run and
+      # a release before anyone noticed.
+      #
+      # Both of gofmt's failure modes need handling, and they are not alike. A file that
+      # is merely misformatted is listed on stdout with exit 0 -- so the failure has to
+      # be raised by hand. A file that does not parse is the opposite: nothing on stdout
+      # and exit 2, which a naive `[ -n "$unformatted" ]` reads as success. The first
+      # draft of this step had exactly that hole.
+      - name: Format
+        run: |
+          if ! unformatted=$(gofmt -l .); then
+            echo "::error::gofmt could not parse the tree"
+            gofmt -l .    # re-run unredirected so the parse errors reach the log
+            exit 1
+          fi
+          if [ -n "$unformatted" ]; then
+            echo "::error::not gofmt'd:"
+            echo "$unformatted"
+            gofmt -d .
+            exit 1
+          fi
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test ./...
+
+  binaries:
+    needs: test
+    runs-on: ubuntu-latest
+    container:
+      image: golang:1.26.6-bookworm
+      volumes:
+        - go-mod-cache:/go/pkg/mod
+        - go-build-cache:/root/.cache/go-build
+        - gobin-cache:/go/bin
+    steps:
+      - name: Checkout
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: git clone --depth=1 --branch "$REF_NAME" "$REPO_URL" .
+
+      - name: Build every target
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          set -eu
+          mkdir -p dist
+          for target in linux/amd64 linux/arm64 darwin/amd64 darwin/arm64; do
+            GOOS="${target%/*}"
+            GOARCH="${target#*/}"
+            out="dist/terdut-${REF_NAME}-${GOOS}-${GOARCH}"
+            echo "building $out"
+            GOOS="$GOOS" GOARCH="$GOARCH" go build \
+              -ldflags "-w -s -X main.version=${REF_NAME}" \
+              -o "$out" ./cmd/terdut
+          done
+
+      # Creating the release is made idempotent rather than assumed-new: a re-run of a
+      # failed release must not die on the release that already exists. Assets are
+      # replaced the same way, so a re-run repairs a partial upload.
+      - name: Publish the release
+        env:
+          REF_NAME: ${{ github.ref_name }}
+          TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          set -eu
+          auth="Authorization: token $TOKEN"
+
+          body=$(curl -sf -H "$auth" "$API/releases/tags/$REF_NAME" || true)
+          if [ -z "$body" ]; then
+            body=$(curl -sf -X POST -H "$auth" -H 'Content-Type: application/json' \
+              -d "{\"tag_name\":\"$REF_NAME\",\"name\":\"$REF_NAME\"}" \
+              "$API/releases")
+          fi
+
+          # The release object serialises `id` first, so the first match is the release's
+          # own id and not one of the nested author/asset ids.
+          release_id=$(printf '%s' "$body" | grep -o '"id":[0-9]*' | head -1 | cut -d: -f2)
+          [ -n "$release_id" ] || { echo "::error::could not determine release id"; exit 1; }
+          echo "release id $release_id"
+
+          for f in dist/*; do
+            name=$(basename "$f")
+            # Drop an existing asset of the same name first: Gitea happily stores two
+            # attachments with one name, and the updater matches by name.
+            old=$(curl -sf -H "$auth" "$API/releases/$release_id/assets" \
+                  | tr '}' '\n' | grep "\"name\":\"$name\"" \
+                  | grep -o '"id":[0-9]*' | head -1 | cut -d: -f2 || true)
+            if [ -n "$old" ]; then
+              curl -sf -X DELETE -H "$auth" "$API/releases/$release_id/assets/$old" || true
+            fi
+            echo "uploading $name"
+            curl -sf -X POST -H "$auth" -F "attachment=@$f" \
+              "$API/releases/$release_id/assets?name=$name" > /dev/null
+          done
+
+  # Host mode on purpose (no `container:`): this is the only context with a Docker CLI
+  # pointed at the dind daemon. A `container:` job would sit on the dind bridge with no
+  # docker socket at all.
+  image:
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: git clone --depth=1 --branch "$REF_NAME" "$REPO_URL" .
+
+      - name: Log in to the registry
+        env:
+          TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: echo "$TOKEN" | docker login "$REGISTRY" -u niklas --password-stdin
+
+      # The default "docker" driver cannot build more than one platform at a time; the
+      # docker-container driver can. Reused across runs if it survived the last one.
+      - name: Prepare buildx
+        run: docker buildx create --name terdut --use 2>/dev/null || docker buildx use terdut
+
+      # No QEMU: the Dockerfile's builder stage runs on $BUILDPLATFORM and cross-compiles
+      # from TARGETARCH, so both platforms build natively. See the comment in Dockerfile.
+      - name: Build and push
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          docker buildx build \
+            --platform linux/amd64,linux/arm64 \
+            --build-arg "VERSION=${REF_NAME}" \
+            --tag "${IMAGE}:latest" \
+            --tag "${IMAGE}:${REF_NAME}" \
+            --push .
+
+  # Also host mode: helm is baked into the runner image, and a `container:` job could not
+  # install it -- get.helm.sh is unreachable from the dind bridge.
+  chart:
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: git clone --depth=1 --branch "$REF_NAME" "$REPO_URL" .
+
+      # This job is the only thing that publishes the chart, which is what keeps the
+      # published metadata honest. There used to be a second publisher on every charts/**
+      # push to main, and the two raced for the same chart version with different answers:
+      # this one stamps version and appVersion from the tag, that one took Chart.yaml
+      # verbatim, where appVersion is the hardcoded "latest". Whichever landed first won,
+      # so the metadata of a release depended on which runner was quicker -- chart 0.9.0
+      # went out on 2026-08-08 reading appVersion "latest" that way.
+      #
+      # It could not be fixed by making both agree: the tag is pushed after the branch, so
+      # a workflow triggered by the main push cannot know the version it is about to be
+      # tagged with. One publisher, triggered by the tag.
+      #
+      # The cost is that the chart only ships with an app release. That is no real loss --
+      # the sed below ties the chart version to the app version, so a chart-only change
+      # has no version of its own to be released under anyway. Chart fixes ride the next
+      # tag.
+      - name: Stamp the chart version from the tag
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          set -eu
+          if ! echo "$REF_NAME" | grep -qE '^v[0-9]'; then
+            echo "::error::refusing to publish a chart for non-version tag ${REF_NAME}"
+            exit 1
+          fi
+          CHART_VERSION="${REF_NAME#v}"
+          sed -i "s/^version:.*/version: ${CHART_VERSION}/" charts/terdut-server/Chart.yaml
+          sed -i "s/^appVersion:.*/appVersion: \"${REF_NAME}\"/" charts/terdut-server/Chart.yaml
+          cat charts/terdut-server/Chart.yaml
+
+      - name: Package and push
+        env:
+          REF_NAME: ${{ github.ref_name }}
+          TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          set -eu
+          echo "$TOKEN" | helm registry login "$REGISTRY" -u niklas --password-stdin
+          # Isolated repo config: the machine-wide helm repo list is not this job's
+          # business, and one unreachable entry in it aborts otherwise-fine commands.
+          # HELM_REPOSITORY_CACHE is deliberately NOT overridden alongside it -- helm
+          # writes a refreshed index to the default cache and then looks for it in the
+          # overridden one.
+          export HELM_REPOSITORY_CONFIG="$PWD/.helm-repos.yaml"
+          : > "$HELM_REPOSITORY_CONFIG"
+          helm package charts/terdut-server -d dist
+          helm push "dist/terdut-server-${REF_NAME#v}.tgz" "oci://${REGISTRY}/niklas"

.github/workflows/chart-release.yml

@@ -1,38 +0,0 @@
-name: Release Helm Chart
-
-on:
-  push:
-    branches:
-      - main
-    paths:
-      - charts/**
-
-jobs:
-  release:
-    runs-on: ubuntu-latest
-    permissions:
-      contents: write
-      pages: write
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-
-      - name: Configure Git
-        run: |
-          git config user.name "$GITHUB_ACTOR"
-          git config user.email "$GITHUB_ACTOR@users.noreply.github.com"
-
-      - name: Install Helm
-        uses: azure/setup-helm@v4
-
-      - name: Run chart-releaser
-        uses: helm/chart-releaser-action@v1.6.0
-        with:
-          # A charts/** push without a Chart.yaml version bump would otherwise
-          # fail trying to re-release the current version. Tagged releases also
-          # publish the chart from release.yml, so the two can race.
-          skip_existing: true
-        env:
-          CR_TOKEN: "${{ secrets.GITHUB_TOKEN }}"

.github/workflows/ci.yml

@@ -1,34 +0,0 @@
-name: CI
-
-# The release workflow gates a tag, which is late: a broken commit sits green
-# until somebody decides to publish. This runs the same checks on the way in.
-#
-# push is scoped to main rather than all branches for two reasons: a branch
-# pushed as part of a pull request would otherwise be checked twice, and
-# gh-pages holds the published Helm chart index with no Go code in it, so
-# `go vet ./...` there would fail on a missing go.mod.
-on:
-  push:
-    branches: [main]
-  pull_request:
-
-# A rapid series of pushes only needs the last one checked.
-concurrency:
-  group: ci-${{ github.ref }}
-  cancel-in-progress: true
-
-jobs:
-  test:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-
-      - name: Vet
-        run: go vet ./...
-
-      - name: Test
-        run: go test ./...

.github/workflows/release.yml

@@ -1,143 +0,0 @@
-name: Release
-
-on:
-  push:
-    tags:
-      - 'v*'
-  workflow_dispatch:
-
-jobs:
-  # Gates every publishing job below. A tag that fails here publishes nothing:
-  # the binaries, the image and the chart are all downstream of it.
-  test:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-
-      - name: Vet
-        run: go vet ./...
-
-      - name: Test
-        run: go test ./...
-
-  build:
-    needs: test
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        include:
-          - goos: linux
-            goarch: amd64
-          - goos: linux
-            goarch: arm64
-          - goos: darwin
-            goarch: amd64
-          - goos: darwin
-            goarch: arm64
-
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-
-      - name: Build
-        env:
-          GOOS: ${{ matrix.goos }}
-          GOARCH: ${{ matrix.goarch }}
-        run: |
-          go build \
-            -ldflags "-w -s -X main.version=${{ github.ref_name }}" \
-            -o terdut-${{ github.ref_name }}-${{ matrix.goos }}-${{ matrix.goarch }} \
-            ./cmd/terdut
-
-      - uses: actions/upload-artifact@v4
-        with:
-          name: terdut-${{ github.ref_name }}-${{ matrix.goos }}-${{ matrix.goarch }}
-          path: terdut-${{ github.ref_name }}-${{ matrix.goos }}-${{ matrix.goarch }}
-
-  docker:
-    needs: test
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Log in to GHCR
-        uses: docker/login-action@v3
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Build and push
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          platforms: linux/amd64,linux/arm64
-          push: true
-          build-args: VERSION=${{ github.ref_name }}
-          tags: |
-            ghcr.io/yeniklas/terdut-server:latest
-            ghcr.io/yeniklas/terdut-server:${{ github.ref_name }}
-
-  chart:
-    needs: test
-    runs-on: ubuntu-latest
-    permissions:
-      contents: write
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-
-      - name: Configure Git
-        run: |
-          git config user.name "$GITHUB_ACTOR"
-          git config user.email "$GITHUB_ACTOR@users.noreply.github.com"
-
-      - name: Install Helm
-        uses: azure/setup-helm@v4
-
-      - name: Update chart versions
-        run: |
-          VERSION="${{ github.ref_name }}"
-          if [[ "$VERSION" =~ ^v[0-9] ]]; then
-            CHART_VERSION="${VERSION#v}"
-            sed -i "s/^version:.*/version: ${CHART_VERSION}/" charts/terdut-server/Chart.yaml
-            sed -i "s/^appVersion:.*/appVersion: \"${VERSION}\"/" charts/terdut-server/Chart.yaml
-          fi
-
-      - name: Run chart-releaser
-        uses: helm/chart-releaser-action@v1.6.0
-        with:
-          skip_existing: true
-        env:
-          CR_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
-
-  release:
-    needs: build
-    runs-on: ubuntu-latest
-    permissions:
-      contents: write
-    steps:
-      - uses: actions/download-artifact@v4
-        with:
-          merge-multiple: true
-
-      - uses: softprops/action-gh-release@v2
-        with:
-          files: 'terdut-*'

.release.conf

@@ -0,0 +1,17 @@
+# Read by the `release` skill (~/.claude/skills/release).
+#
+# Only what the Makefile cannot already say. IMAGE, HELM_CHART and HELM_REPO come from
+# `make release-vars`, so they have one definition and cannot drift from what is built.
+#
+# Defaults, set here only where this repo differs:
+#   CHARTS_REPO=$HOME/git/charts   CHARTS_DIR=<image basename>
+#   GITEA_LOGIN=Ryuvia            APPVERSION_PREFIX=
+
+# Same as the image basename, so this is only stated to be read rather than derived.
+CHARTS_DIR=terdut-server
+
+# riksdata writes appVersion: "v0.3.1", rd-web writes a bare 0.5.0; this repo writes the
+# v, like riksdata. Nothing reads the field -- .gitea/workflows/release.yaml stamps both
+# version and appVersion from the tag when it publishes -- but people read it, and until
+# 2026-09-01 it said "latest" while the tree headed for a numbered release.
+APPVERSION_PREFIX=v

Dockerfile

@@ -1,10 +1,19 @@
-FROM golang:1.25-alpine AS builder
+# --platform=$BUILDPLATFORM pins the builder to the machine doing the building, so a
+# multi-arch build compiles both targets natively instead of running an emulated arm64
+# toolchain under QEMU. Go cross-compiles from TARGETOS/TARGETARCH, which BuildKit fills
+# in per platform. The CI runner has no binfmt registration and no way to get one (the
+# JS action that used to install it cannot run there), so this is not just an
+# optimisation -- it is what makes the arm64 image buildable at all.
+FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS builder
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
 ARG VERSION=dev
-RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s -X main.version=${VERSION}" -o /terdut ./cmd/terdut
+ARG TARGETOS
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+    go build -ldflags="-w -s -X main.version=${VERSION}" -o /terdut ./cmd/terdut
 
 FROM scratch
 COPY --from=builder /terdut /terdut

Makefile

@@ -0,0 +1,84 @@
+REGISTRY  := git.ryuvia.com
+# The personal namespace, not ryuvia — deliberately, and for one reason: Gitea
+# scopes package visibility to the owner with no per-package override, so
+# ryuvia/* is private because the org is. Publishing here keeps the image and
+# chart anonymously pullable, so no pull secret is needed in the cluster and
+# Flux needs no registry credentials. Same choice riksdata and rd-web made.
+OWNER     := niklas
+
+IMAGE      := $(REGISTRY)/$(OWNER)/terdut-server
+HELM_CHART := charts/terdut-server
+HELM_REPO  := oci://$(REGISTRY)/$(OWNER)
+
+# go.mod pins an exact patch release so nobody builds the shipped binary with a
+# toolchain carrying known stdlib CVEs. Fedora's Go package overrides the
+# upstream GOTOOLCHAIN default to `local`, which turns that pin into a hard
+# failure on a dev box one patch behind, so restore the upstream default here.
+export GOTOOLCHAIN ?= auto
+
+.PHONY: help
+help: ## Show this help
+	@grep -hE '^[a-zA-Z_-]+:.*?## ' $(MAKEFILE_LIST) | \
+		awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-22s\033[0m %s\n", $$1, $$2}'
+
+## --- checks ---
+#
+# These three mirror .gitea/workflows/ci.yaml step for step, so a green `make fmt
+# lint test` here means the same thing CI means. The one deliberate difference is
+# -race below.
+
+.PHONY: test
+test: ## Run the test suite
+	go test -race ./...
+
+# CI runs a bare `go test ./...`. This is stricter on purpose: the sweeper, the
+# notifier goroutine and the deadman sweep all touch the same single-connection
+# database, and a race there would surface as a flaky production incident rather
+# than a failed build. It passes today; if it ever costs more than it catches,
+# the honest fix is to teach CI -race too, not to quietly drop it here.
+.PHONY: lint
+lint: ## go vet
+	go vet ./...
+
+# Copied from ci.yaml rather than simplified, because both of gofmt's failure
+# modes need handling and they are not alike. A file that is merely misformatted
+# is listed on stdout with exit 0 — so the failure has to be raised by hand. A
+# file that does not parse is the opposite: nothing on stdout and exit 2, which a
+# naive `[ -n "$$out" ]` reads as success. See 9046f6e.
+.PHONY: fmt
+fmt: ## Report unformatted files
+	@if ! unformatted=$$(gofmt -l .); then \
+		echo "gofmt could not parse the tree:"; gofmt -l .; exit 1; \
+	fi; \
+	if [ -n "$$unformatted" ]; then \
+		echo "gofmt needed:"; echo "$$unformatted"; gofmt -d .; exit 1; \
+	fi
+
+.PHONY: helm-lint
+helm-lint: ## Lint and render the chart
+	helm lint $(HELM_CHART) --set image.tag=v0.0.0
+	helm template terdut-server $(HELM_CHART) --namespace terdut-server \
+		--set image.tag=v0.0.0 >/dev/null
+	@# networking.listener defaults to "", which attaches the route to every
+	@# matching listener including plaintext HTTP. Production sets it, so the
+	@# default render proves nothing about the path that actually ships.
+	helm template terdut-server $(HELM_CHART) --namespace terdut-server \
+		--set image.tag=v0.0.0 --set networking.listener=https-terdut >/dev/null
+
+## --- release ---
+
+# The release process (~/.claude/skills/release) reads these rather than restating them.
+# One definition, so the version that gets tagged, the image that gets pushed and the chart
+# the wrapper pins cannot drift apart in a second copy.
+.PHONY: release-vars
+release-vars: ## Print the variables the release process reads
+	@printf 'IMAGE=%s\nHELM_CHART=%s\nHELM_REPO=%s\n' '$(IMAGE)' '$(HELM_CHART)' '$(HELM_REPO)'
+
+# There is deliberately no build/push/helm-package/helm-push/release here, unlike
+# riksdata and rd-web. .gitea/workflows/release.yaml owns publishing for this repo,
+# and it does two things a local make cannot: it builds linux/amd64 and linux/arm64
+# through buildx, and it stamps the chart's version and appVersion from the tag. A
+# `docker build && docker push` target would push a single-architecture image over
+# the multi-arch tag, which is both easy to do by accident and invisible afterwards
+# — the tag would still resolve, just not on arm64. Publishing happens by pushing a
+# tag; nothing else.

README.md

@@ -17,7 +17,7 @@ Incident management server for teams using Prometheus Alertmanager.
 **Prerequisites:** Go 1.21+
 
 ```bash
-git clone https://github.com/yeniklas/terdut-server
+git clone https://git.ryuvia.com/niklas/terdut-server
 cd terdut-server
 go run ./cmd/terdut
 ```
@@ -52,11 +52,12 @@ docker run -p 8080:8080 -v $(pwd)/data:/data \
 
 ### Kubernetes
 
-A Helm chart is published from this repository:
+A Helm chart is published from this repository as an OCI artifact, versioned in lockstep
+with the app — chart `x.y.z` is always app `vx.y.z`:
 
 ```bash
-helm repo add terdut-server https://yeniklas.github.io/terdut-server
-helm upgrade --install terdut-server terdut-server/terdut-server \
+helm upgrade --install terdut-server oci://git.ryuvia.com/niklas/terdut-server \
+  --version 0.9.0 \
   --namespace terdut-server --create-namespace \
   --set networking.hostname=terdut.example.com
 ```
@@ -71,10 +72,25 @@ than an `Ingress`. TLS is terminated at the gateway, so the server itself never
 | `networking.listener` | `""` | Gateway listener (`sectionName`) to bind to. Empty attaches to every matching listener, **including plaintext HTTP** — set it to the HTTPS listener's name to serve TLS only |
 | `networking.servicePort` | `8080` | Port the route forwards to; keep in sync with `service.port` |
 | `bootstrap.enabled` | `true` | Runs a post-install hook that creates the first user and stores its API key in the `<release>-admin-key` Secret. Already-bootstrapped servers are left alone |
+| `backupSidecar.enabled` | `true` | Adds an idle `python` sidecar and the [k8up](https://k8up.io/) annotations that dump the database through it |
 
 The API key travels in an `Authorization: Bearer` header, so set `networking.listener` whenever the
 hostname is reachable outside a trusted network.
 
+#### Backups
+
+The server image is `FROM scratch` — the binary and nothing else — so there is no interpreter to
+run a database dump in, and the database runs in WAL mode, where a file-level copy of the volume is
+not crash-consistent. The chart therefore ships an idle `python:*-alpine` sidecar that shares the
+data volume, and points k8up's `backupcommand` at it with `k8up.io/backupcommand-container`. Without
+that annotation k8up execs into `.spec.containers[0]` and the dump fails.
+
+The dump is buffered and sanity-checked before its first byte reaches stdout, because k8up streams
+stdout straight into Restic: a dump that dies partway is otherwise stored as a silently truncated
+snapshot that k8up still reports as successful.
+
+Set `backupSidecar.enabled=false` if you back the volume up some other way.
+
 ---
 
 ## Configuration
@@ -85,10 +101,22 @@ hostname is reachable outside a trusted network.
 | `TERDUT_DB_PATH` | `terdut.db` | Path to the SQLite database file |
 | `TERDUT_ARCHIVE_AFTER` | `168h` (7d) | How long a resolved alert or incident stays in the default list before being auto-archived |
 | `TERDUT_STALE_AFTER` | `6h` | How long a firing alert may go without a refreshing webhook before it is treated as resolved — **must exceed your Alertmanager `repeat_interval`** |
+| `TERDUT_DEADMAN_MATCHERS` | `alertname=Watchdog` | Which alerts are [dead man's switches](#dead-mans-switch). `;` separates matchers, `,` the label conditions within one, `=` is exact equality. Every matcher must name an `alertname` |
+| `TERDUT_DEADMAN_TIMEOUT` | `15m` | How long a heartbeat may go unheard before its switch is declared dead — **must be shorter than the `repeat_interval` of the route carrying it**. `0` disables dead man's switch handling |
+| `TERDUT_DEADMAN_SEVERITY` | `critical` | Severity a dead man's switch incident opens at |
+| `TERDUT_NTFY_URL` | — | ntfy server to publish push notifications to. Empty disables notifications entirely |
+| `TERDUT_NTFY_TOKEN` | — | Bearer token for an access-controlled ntfy |
+| `TERDUT_NTFY_FALLBACK_TOPIC` | — | Topic used when nobody is on call |
+| `TERDUT_PUBLIC_URL` | — | Base URL a phone uses to reach this server, for the link and Acknowledge button inside a notification |
+| `TERDUT_NOTIFY_REPEAT` | `15m` | How long an incident may sit unacknowledged before it is paged again. `0` notifies once and never repeats |
 
 Durations use Go syntax (`30m`, `12h`, `168h`). An unparseable value falls back to the default.
 
-In the Helm chart the two sweeper durations are set via `sweeper.staleAfter` and `sweeper.archiveAfter`.
+Note that `TERDUT_STALE_AFTER` and `TERDUT_DEADMAN_TIMEOUT` point in opposite directions. Staleness
+is a generous grace period around a `repeat_interval` you do not control; a dead man's switch is a
+deadline you set deliberately, and the heartbeat's route is configured to beat faster than it.
+
+In the Helm chart the two sweeper durations are set via `sweeper.staleAfter` and `sweeper.archiveAfter`, dead man's switches via the `deadman.*` values, and notifications via the `notify.*` values.
 
 ---
 
@@ -109,6 +137,30 @@ route:
 
 The webhook endpoint requires no authentication.
 
+If you use the [dead man's switch](#dead-mans-switch) — and the default configuration does — give
+the heartbeat a route of its own, because the deadline is only as tight as the interval feeding it:
+
+```yaml
+route:
+  receiver: terdut
+  repeat_interval: 4h
+  routes:
+    - matchers: [ 'alertname = "Watchdog"' ]
+      receiver: terdut
+      group_wait: 0s
+      group_interval: 1m
+      repeat_interval: 1m
+```
+
+That delivers a heartbeat every **2 minutes**, not every minute. Alertmanager only reconsiders a
+group every `group_interval`, and at exactly one elapsed interval `repeat_interval` has not *quite*
+passed, so the send slips to the next tick — equal values give 2×. Two minutes against the 15 minute
+default is seven heartbeats per window, which is the point; use `group_interval: 30s` if you want
+the numbers to mean what they say.
+
+kube-prometheus-stack users get the `Watchdog` alert (`expr: vector(1)`) for free; it just needs
+routing to terdut rather than to `null`.
+
 ---
 
 ## Alerts and incidents
@@ -159,6 +211,10 @@ alert that never stopped firing.
   that group opens a *new* incident rather than reopening this one. If the alert
   underneath never stops firing, the incident stays closed — that is what
   resolving by hand asserts.
+- **On recovery**, for a [dead man's switch](#dead-mans-switch) incident whose
+  heartbeat started arriving again (`"resolution_source": "recovered"`). These
+  incidents have no member alerts, so the automatic cascade above cannot reach
+  them.
 
 To quieten an incident you expect to come back, snooze it instead
 (`POST /api/incidents/{id}/snooze`). A snooze hides the incident from the default
@@ -170,6 +226,64 @@ A new incident is assigned to whoever holds today's schedule entry at the moment
 it opens (`GET /api/schedule/current`). If nobody is scheduled it opens
 unassigned. Reassign with `POST /api/incidents/{id}/assign`.
 
+One person holds a given day, so `POST /api/schedule` refuses a date somebody
+already has: taking a shift off the person expecting to be paged for it should
+not be something a plain call does by accident. Pass `"replace": true` to take
+them anyway. Either way the whole request is one transaction — a week where some
+days are free and some are taken moves as a unit, and a failure leaves the rota
+exactly as it was rather than with a hole in it.
+
+### Push notifications
+
+With `TERDUT_NTFY_URL` set, an incident that opens is pushed to the on-call
+person's phone through [ntfy](https://ntfy.sh). Set each user's topic with
+`PUT /api/users/{id}/notify`; a user with no topic falls back to
+`TERDUT_NTFY_FALLBACK_TOPIC`, as does an incident that opens with nobody on call.
+If neither yields a topic, nothing is queued.
+
+Three things get pushed:
+
+- **triggered** — an incident opened. Priority follows severity (`critical` maps
+  to ntfy's max priority, the one that overrides the phone's quiet settings).
+- **reminder** — the incident is still `triggered` after `TERDUT_NOTIFY_REPEAT`.
+  Repeats until somebody acts. Acknowledging, snoozing, resolving or archiving
+  all stop it — snooze is the mute button.
+- **resolved** — every alert under the incident stopped firing. Only sent to
+  whoever was paged in the first place, and only for the automatic cascade:
+  resolving by hand pushes nothing, since the person who did it already knows.
+
+Notifications carry an **Acknowledge** button that acknowledges the incident
+without opening anything. It POSTs to `/api/notify/ack/{token}`, an
+unauthenticated route authorised by the 256-bit token in its path — minted fresh
+per notification, scoped to one incident and one action, and valid for 24 hours.
+A real API key is never put in a notification, because the message is stored on
+the ntfy server and cached on the device.
+
+The token is **not** consumed by use. Acknowledging is idempotent, so a token
+stays valid for its full 24 hours and a second tap is a no-op that reports the
+incident's current state rather than an error — which is what you want when a
+tap is retried on a flaky mobile connection. What bounds it is scope, not a use
+count: one incident, one action, one day. Expired tokens are purged by the
+sweeper.
+
+Two consequences worth planning for:
+
+- `/api/notify/ack/{token}` **must stay publicly reachable**, or the button will
+  not work when the responder is off your network.
+- Notifications sent to the fallback topic carry **no** Acknowledge button. The
+  topic is shared, and a button on it would let any subscriber acknowledge as
+  somebody else.
+
+Delivery is a queue, not an inline call: the webhook writes a row and a
+background notifier sends it within 30 seconds, retrying with exponential
+backoff up to 8 attempts. Nothing about ingestion blocks on ntfy being reachable.
+
+Every delivery is recorded on the incident's timeline: a `notified` event once
+ntfy accepts the publish, and a `notify_failed` event when a notification
+exhausts its retries. Written from the result rather than at enqueue, so the
+timeline says what actually happened — and a page that never landed is visible
+instead of looking the same as one that did.
+
 ### Stale alert expiry
 
 A resolved webhook is the only signal that an alert has stopped firing, so a
@@ -189,6 +303,72 @@ to distinguish them from a real Alertmanager resolve (`"alertmanager"`).
 An expiry cascades: once it leaves an incident with nothing firing under it, the
 incident resolves too, in the same sweep.
 
+### Dead man's switch
+
+Everything above assumes alerts arrive. If Prometheus stops evaluating, or
+Alertmanager cannot reach this server, nothing arrives — and silence looks
+exactly like everything being fine. A dead man's switch inverts the handling for
+one designated alert so that silence is the signal:
+
+- **receiving** it opens no incident, and
+- the **absence** of it does.
+
+kube-prometheus-stack already ships the alert for this. `Watchdog` is
+`expr: vector(1)`, so it fires permanently and is re-sent forever; it is worth
+nothing unless something downstream notices it stop. That is what
+`TERDUT_DEADMAN_MATCHERS` defaults to.
+
+A matcher is a set of exact label conditions, one of which must be the
+`alertname`:
+
+```
+TERDUT_DEADMAN_MATCHERS="alertname=Watchdog,cluster=prod; alertname=EdgeHeartbeat"
+```
+
+**The unit of monitoring is the fingerprint, not the alert name.** Two clusters
+sending the same `Watchdog` are two independent switches, so a healthy one can
+never mask a dead one.
+
+#### The lifecycle
+
+A switch is **dormant** until its first heartbeat arrives. A configured matcher
+that has never been heard from opens nothing, so a fresh deploy or a restored
+database does not page. It also means a matcher that never matches anything is
+silently inert — check the startup log line, which lists the matchers that
+survived parsing.
+
+Once armed, the sweeper declares it **dead** when either the heartbeat has not
+been refreshed within `TERDUT_DEADMAN_TIMEOUT`, or Alertmanager explicitly
+resolved it — the sender saying the heartbeat stopped needs no further waiting.
+That opens an incident at `TERDUT_DEADMAN_SEVERITY`, assigned and paged like any
+other, and marks the heartbeat alert `"resolution_source": "deadman"` so the
+alert list stops claiming a dead switch is firing.
+
+It **recovers** when the heartbeat starts arriving again: the incident resolves
+with `"resolution_source": "recovered"` and the all-clear goes to whoever was
+paged.
+
+Resolving the incident by hand sticks, the same way it does for an alert-backed
+one. While the switch stays silent nothing new opens — so a decommissioned
+source is a one-time page rather than a nag. The switch **re-arms** on the next
+heartbeat: come back and die again, and that is a new incident.
+
+#### Two things to know
+
+`TERDUT_DEADMAN_TIMEOUT` must be **shorter** than the `repeat_interval` of the
+route carrying the heartbeat, which is the exact opposite of
+`TERDUT_STALE_AFTER`. Inheriting a default `repeat_interval` of 4h gives you a
+switch that takes four hours to notice anything, so give the heartbeat
+[its own route](#alertmanager-configuration). Matched alerts are exempt from
+stale-alert expiry — a heartbeat answers to its own timeout and nothing else.
+
+A dead man's switch incident has **no member alerts**:
+`GET /api/incidents/{id}/alerts` returns an empty list. There is no alert
+describing the problem, because the problem is that no alert arrived. What
+happened is on the timeline instead, as a `deadman_silent` event carrying the age
+of the last heartbeat, and the heartbeat's labels are on the incident's
+`group_labels`.
+
 ---
 
 ## API reference
@@ -209,6 +389,7 @@ Authorization: Bearer <api-key>
 | `GET` | `/api/users` | List users |
 | `POST` | `/api/users` | Create user `{"username","email"}` |
 | `DELETE` | `/api/users/{id}` | Delete user (cascades to keys) |
+| `PUT` | `/api/users/{id}/notify` | Set push notification target `{"ntfy_topic"}` — empty string clears it |
 | `POST` | `/api/users/{id}/api-keys` | Issue API key `{"name"}` — key shown once |
 | `DELETE` | `/api/users/{id}/api-keys/{keyID}` | Revoke API key |
 
@@ -218,6 +399,12 @@ Authorization: Bearer <api-key>
 |---|---|---|
 | `POST` | `/api/alertmanager/webhook` | Alertmanager v4 webhook receiver (no auth) |
 
+### Notifications
+
+| Method | Path | Description |
+|---|---|---|
+| `POST` | `/api/notify/ack/{token}` | Acknowledge an incident from a push notification's Acknowledge button. No auth: the token in the path is the credential — one incident, one action, 24 hours, idempotent. Must stay publicly reachable |
+
 ### Incidents
 
 | Method | Path | Description |
@@ -260,7 +447,7 @@ only by their author. The rest of the timeline is a record of what happened.
 | `assigned_to_id` / `assigned_to` | | *optional* — user id, username |
 | `snoozed_until` | timestamp | *optional* — a value in the past reads as not snoozed |
 | `resolved_at` | timestamp | *optional* |
-| `resolution_source` | string | *optional* — `"alerts"` or `"manual"` |
+| `resolution_source` | string | *optional* — `"alerts"`, `"manual"` or `"recovered"` |
 | `archived_at` | timestamp | *optional* |
 | `alerts` | array | Only on `GET /api/incidents/{id}` |
 
@@ -281,8 +468,16 @@ name: degrade unknown values to "resolved, reason unknown".
 
 Types written today: `triggered`, `alert_added`, `alert_resolved`,
 `acknowledged`, `unacknowledged`, `assigned`, `snoozed`, `unsnoozed`, `resolved`,
-`note`. On an `assigned` event `user_id` is the **assignee**, not the actor. New
-types may be added; render unknown ones generically rather than dropping them.
+`note`, `notified`, `notify_failed`, `deadman_silent`. On an `assigned` event
+`user_id` is the **assignee**, not the actor. New types may be added; render
+unknown ones generically rather than dropping them.
+
+On `notified` and `notify_failed`, `detail` carries the notification kind
+(`triggered` | `reminder` | `resolved`), and on a failure the reason after it.
+`user_id` is who was paged — absent means the page went to the shared fallback
+topic and so belongs to nobody. The topic itself is never written to the
+timeline: it is a shared secret with the ntfy server, and every API key can read
+this.
 
 ### Alerts
 
@@ -297,7 +492,8 @@ Archived alerts are hidden from `GET /api/alerts` unless `?archived=true` is
 passed; alert archiving is automatic housekeeping by the sweeper, not a user
 action. Resolved alerts carry `resolution_source`: `"alertmanager"` for a real
 resolved webhook, `"expiry"` when the sweeper inferred it (see
-[Stale alert expiry](#stale-alert-expiry)).
+[Stale alert expiry](#stale-alert-expiry)), `"deadman"` for a heartbeat declared
+dead (see [Dead man's switch](#dead-mans-switch)).
 
 #### The alert object
 
@@ -318,7 +514,7 @@ when unset, so clients must treat them as nullable.
 | `generator_url` | string | Link back to the originating Prometheus |
 | `received_at` | timestamp | When the server last accepted a webhook for this alert — see below |
 | `incident_id` | integer | *optional* — the most recent incident this alert belongs to |
-| `resolution_source` | string | *optional* — `"alertmanager"` or `"expiry"` |
+| `resolution_source` | string | *optional* — `"alertmanager"`, `"expiry"` or `"deadman"` |
 | `archived_at` | timestamp | *optional* — set while archived |
 
 ##### `received_at` is a liveness heartbeat
@@ -373,6 +569,13 @@ which happened. Clients may rely on this:
   worthwhile, since `"expiry"` can also mean the alert is still firing and the
   notification path broke.
 
+- **`"deadman"` — a heartbeat was declared dead** (see
+  [Dead man's switch](#dead-mans-switch)). Like `"expiry"`, an inference from
+  silence rather than an observed end, so `ends_at` is approximate — but a much
+  tighter one, bounded by `TERDUT_DEADMAN_TIMEOUT`. It is also the one resolution
+  a re-fire under the same `starts_at` can undo, since the switch coming back is
+  exactly the evidence that the inference was wrong.
+
 Treat the value as an open set and tolerate ones you do not recognise — new
 sources may be added, and unknown values should degrade to "resolved, reason
 unknown" rather than being rejected.
@@ -381,7 +584,7 @@ unknown" rather than being rejected.
 
 | Method | Path | Description |
 |---|---|---|
-| `POST` | `/api/schedule` | Assign user to dates `{"user_id", "dates":["YYYY-MM-DD",...]}` — all-or-nothing |
+| `POST` | `/api/schedule` | Assign user to dates `{"user_id", "dates":["YYYY-MM-DD",...], "replace"}` — all-or-nothing |
 | `GET` | `/api/schedule` | List entries. Filters: `?from=YYYY-MM-DD`, `?to=YYYY-MM-DD` |
 | `GET` | `/api/schedule/current` | Today's on-call user (UTC), 404 if none |
 | `DELETE` | `/api/schedule/{id}` | Remove schedule entry |
@@ -429,6 +632,26 @@ Nothing about the two documented alert contracts changes: `received_at` is still
 advanced on every accepted webhook, and `resolution_source` still means what it
 did.
 
+## Upgrading to dead man's switches
+
+Dead man's switch handling is **on by default**, watching `alertname=Watchdog`
+with a 15 minute timeout. If you already route `Watchdog` to this server, the
+behaviour of that alert changes on upgrade, in both directions:
+
+- it stops opening incidents when it arrives, and
+- it starts opening one when it stops arriving.
+
+**Check your `repeat_interval` before upgrading.** The switch pages whenever a
+heartbeat has not been refreshed within `TERDUT_DEADMAN_TIMEOUT`, so a `Watchdog`
+route inheriting a 4h or 12h `repeat_interval` will page constantly against the
+15 minute default. Either give the heartbeat
+[its own fast route](#alertmanager-configuration) — the point of the feature — or
+set `TERDUT_DEADMAN_TIMEOUT` above your current `repeat_interval` until you have.
+`TERDUT_DEADMAN_TIMEOUT=0` turns the whole thing off.
+
+There is no migration and no schema change. An existing open incident from a
+`Watchdog` that arrived under the old behaviour is unaffected; resolve it by hand.
+
 ---
 
 ## Development

charts/terdut-server/Chart.yaml

@@ -2,5 +2,17 @@ apiVersion: v2
 name: terdut-server
 description: A Helm chart for Terminal Duty — on-call alert management server
 type: application
-version: 0.5.0
-appVersion: "latest"
+# These two are placeholders for a local `helm install ./charts/terdut-server`, not the
+# released values. .gitea/workflows/release.yaml rewrites both from the git tag when it
+# publishes, so the chart version always equals the app version.
+#
+# They are kept in step with the tag anyway. Being read is the only thing these two
+# lines do -- nothing that publishes looks at them -- and a tree heading for v0.9.2 that
+# says 0.9.0 tells its reader something false. That is what they said until 2026-09-01,
+# through two releases.
+#
+# appVersion and image.tag in values.yaml no longer agree, and that is not an oversight:
+# image.tag stays "latest", which is what a local install actually pulls. appVersion is
+# metadata and drives nothing.
+version: 0.9.2
+appVersion: "v0.9.2"

charts/terdut-server/templates/deployment.yaml

@@ -10,10 +10,50 @@ spec:
   selector:
     matchLabels:
       {{- include "terdut-server.selectorLabels" . | nindent 6 }}
+  # The data PVC is ReadWriteOnce, so a RollingUpdate deadlocks: the new pod
+  # cannot attach the volume until the old one releases it, and the old one is
+  # not torn down until the new one is ready.
+  strategy:
+    type: Recreate
   template:
     metadata:
       labels:
         {{- include "terdut-server.selectorLabels" . | nindent 8 }}
+      {{- if .Values.backupSidecar.enabled }}
+      annotations:
+        # Dumps the whole database: incidents, alerts, users, API key hashes,
+        # the schedule and the notification outbox.
+        #
+        # Runs in the `backup` sidecar, NOT in the app container: the server
+        # image is FROM scratch and has no interpreter at all. k8up execs into
+        # .spec.containers[0] unless told otherwise, hence the explicit
+        # k8up.io/backupcommand-container.
+        #
+        # Buffered and sanity-checked before the first byte reaches stdout: k8up
+        # streams stdout straight into restic, so a dump that dies partway is
+        # stored as a silently-truncated snapshot that k8up still reports as
+        # Succeeded. The check counts users rather than incidents -- incidents
+        # are swept and archived, so an empty incidents table is a legitimate
+        # state, whereas a database with no users never is.
+        #
+        # The connection is read-only but the mount is not: the database runs in
+        # WAL mode, and opening it mode=ro still needs write access to the -shm
+        # wal-index.
+        #
+        # chr(10), not '\n': k8up parses this annotation with go-shellquote.
+        k8up.io/backupcommand-container: backup
+        k8up.io/backupcommand: >-
+          python3 -c "import sqlite3, sys;
+          con = sqlite3.connect('file:/data/terdut.db?mode=ro', uri=True);
+          con.execute('BEGIN');
+          users = con.execute('SELECT count(*) FROM users').fetchone()[0];
+          out = chr(10).join(con.iterdump()) + chr(10);
+          (users > 0 and out.rstrip().endswith('COMMIT;'))
+          or sys.exit('terdut: db dump failed sanity checks');
+          sys.stdout.write(out)"
+        k8up.io/file-extension: ".sql"
+        k8up.io/backup: "true"
+      {{- end }}
     spec:
       enableServiceLinks: false
       containers:
@@ -33,6 +73,29 @@ spec:
               value: "{{ .Values.sweeper.staleAfter }}"
             - name: TERDUT_ARCHIVE_AFTER
               value: "{{ .Values.sweeper.archiveAfter }}"
+            - name: TERDUT_DEADMAN_MATCHERS
+              value: "{{ .Values.deadman.matchers }}"
+            - name: TERDUT_DEADMAN_TIMEOUT
+              value: "{{ .Values.deadman.timeout }}"
+            - name: TERDUT_DEADMAN_SEVERITY
+              value: "{{ .Values.deadman.severity }}"
+            {{- if .Values.notify.ntfyUrl }}
+            - name: TERDUT_NTFY_URL
+              value: "{{ .Values.notify.ntfyUrl }}"
+            - name: TERDUT_NTFY_FALLBACK_TOPIC
+              value: "{{ .Values.notify.fallbackTopic }}"
+            - name: TERDUT_NOTIFY_REPEAT
+              value: "{{ .Values.notify.repeatEvery }}"
+            - name: TERDUT_PUBLIC_URL
+              value: "{{ .Values.notify.publicUrl | default (printf "https://%s" .Values.networking.hostname) }}"
+            {{- if .Values.notify.tokenSecret.name }}
+            - name: TERDUT_NTFY_TOKEN
+              valueFrom:
+                secretKeyRef:
+                  name: {{ .Values.notify.tokenSecret.name }}
+                  key: {{ .Values.notify.tokenSecret.key }}
+            {{- end }}
+            {{- end }}
           volumeMounts:
             - name: data
               mountPath: /data
@@ -46,6 +109,25 @@ spec:
               path: /healthz
               port: http
             initialDelaySeconds: 5
+
+        {{- if .Values.backupSidecar.enabled }}
+        # Idle sidecar. It exists only so k8up has a container with a sqlite3
+        # module to exec the backupcommand in. Mounted read-write on purpose:
+        # see the note on the backupcommand annotation above.
+        - name: backup
+          image: "{{ .Values.backupSidecar.image.repository }}:{{ .Values.backupSidecar.image.tag }}"
+          imagePullPolicy: {{ .Values.backupSidecar.image.pullPolicy }}
+          command: ["sleep", "infinity"]
+          volumeMounts:
+            - name: data
+              mountPath: /data
+          resources:
+            requests:
+              memory: "16Mi"
+              cpu: "10m"
+            limits:
+              memory: "64Mi"
+        {{- end }}
       volumes:
         - name: data
           persistentVolumeClaim:

charts/terdut-server/values.yaml

@@ -7,7 +7,7 @@ networking:
   listener: ""
 
 image:
-  repository: ghcr.io/yeniklas/terdut-server
+  repository: git.ryuvia.com/niklas/terdut-server
   tag: "latest"
   pullPolicy: IfNotPresent
 
@@ -26,6 +26,80 @@ sweeper:
   # How long a resolved alert stays in the default list before auto-archiving.
   archiveAfter: 168h
 
+# Alerts treated as dead man's switches: receiving one opens no incident, and
+# the absence of one does. The Watchdog alert kube-prometheus-stack ships is
+# exactly this — an always-firing alert whose only value is something noticing
+# when it stops.
+deadman:
+  # Which alerts to treat as heartbeats. ";" separates matchers, "," separates
+  # the label conditions within one, "=" is exact equality. Every matcher must
+  # name an alertname:
+  #   alertname=Watchdog,cluster=prod; alertname=EdgeHeartbeat
+  # Each distinct label set is watched independently, so two clusters sending
+  # the same alertname are two switches and a live one cannot mask a dead one.
+  matchers: "alertname=Watchdog"
+  # How long a heartbeat may go unheard before its switch is declared dead.
+  #
+  # This must be SHORTER than the Alertmanager repeat_interval of the route
+  # carrying the heartbeat — the opposite of sweeper.staleAfter. The default
+  # repeat_interval of 4h (12h in many setups) makes for a useless dead man's
+  # switch, so give the heartbeat a route of its own:
+  #
+  #   - matchers: [ 'alertname = "Watchdog"' ]
+  #     receiver: terdut
+  #     group_wait: 0s
+  #     group_interval: 1m
+  #     repeat_interval: 1m
+  #
+  # That delivers every 2m rather than every 1m: a group is only reconsidered
+  # each group_interval, and at exactly one elapsed interval repeat_interval has
+  # not quite passed, so equal values give 2x. Fine against 15m; use
+  # group_interval: 30s if you want a true 1m.
+  #
+  # Set to 0 to disable dead man's switch handling entirely.
+  timeout: 15m
+  # Severity a dead man's switch incident opens at. These incidents have no
+  # member alerts to derive one from, and the heartbeat's own severity label is
+  # meaningless — Watchdog ships as "none". Only "critical" maps to the ntfy
+  # priority that overrides a phone's quiet hours.
+  severity: critical
+
+notify:
+  # ntfy server that push notifications are published to, e.g.
+  # http://ntfy.ntfy.svc.cluster.local. Empty disables notifications entirely.
+  ntfyUrl: ""
+  # Topic used when nobody is on call today. Notifications sent here carry no
+  # Acknowledge button: the topic is shared, so there is no user to attribute an
+  # acknowledgement to. Leave empty to send nothing when the schedule is unset.
+  fallbackTopic: ""
+  # How long an incident may sit unacknowledged before it is paged again.
+  # Set to 0 to notify once and never repeat.
+  repeatEvery: 15m
+  # Base URL a phone uses to reach this server, for the link and the Acknowledge
+  # button inside a notification. Defaults to https://<networking.hostname>.
+  #
+  # The Acknowledge button is a POST to /api/notify/ack/{token} from the
+  # responder's phone, so that path has to stay publicly reachable — it is
+  # authorised by the scoped token in the URL, not by network placement.
+  publicUrl: ""
+  # Optional bearer token for an access-controlled ntfy, read from an existing
+  # Secret. Leave name empty for an open ntfy.
+  tokenSecret:
+    name: ""
+    key: token
+
+# The server image is FROM scratch — just the binary, with no shell, no sqlite3
+# and no python — so a k8up backupcommand cannot run in the app container. This
+# idle sidecar shares the data volume and is selected with
+# k8up.io/backupcommand-container. Only the stdlib sqlite3 module is used, so any
+# python image works.
+backupSidecar:
+  enabled: true
+  image:
+    repository: python
+    tag: "3.13-alpine"
+    pullPolicy: IfNotPresent
+
 bootstrap:
   enabled: true
   username: admin

cmd/terdut/main.go

@@ -8,9 +8,9 @@ import (
 	"syscall"
 	"time"
 
-	"github.com/yeniklas/terdut-server/internal/api"
-	"github.com/yeniklas/terdut-server/internal/config"
-	"github.com/yeniklas/terdut-server/internal/db"
+	"git.ryuvia.com/niklas/terdut-server/internal/api"
+	"git.ryuvia.com/niklas/terdut-server/internal/config"
+	"git.ryuvia.com/niklas/terdut-server/internal/db"
 )
 
 var version = "dev"
@@ -28,7 +28,17 @@ func main() {
 		log.Fatalf("migrate: %v", err)
 	}
 
-	router := api.NewRouter(database)
+	notify := api.NotifyConfig{
+		BaseURL:       cfg.NtfyURL,
+		Token:         cfg.NtfyToken,
+		FallbackTopic: cfg.NtfyFallbackTopic,
+		PublicURL:     cfg.PublicURL,
+		RepeatEvery:   cfg.NotifyRepeat,
+	}
+
+	deadman := api.ParseDeadmanConfig(cfg.DeadmanMatchers, cfg.DeadmanTimeout, cfg.DeadmanSeverity)
+
+	router := api.NewRouter(database, notify, deadman)
 
 	srv := &http.Server{
 		Addr:         cfg.Addr,
@@ -41,7 +51,8 @@ func main() {
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	go api.StartArchiver(ctx, database, cfg.ArchiveAfter, cfg.StaleAfter)
+	go api.StartArchiver(ctx, database, cfg.ArchiveAfter, cfg.StaleAfter, deadman, notify)
+	go api.StartNotifier(ctx, database, notify)
 
 	go func() {
 		log.Printf("terdut-server %s listening on %s", version, cfg.Addr)

go.mod

@@ -1,4 +1,4 @@
-module github.com/yeniklas/terdut-server
+module git.ryuvia.com/niklas/terdut-server
 
 go 1.25.9
 

internal/api/alertmanager.go

@@ -14,6 +14,12 @@ import (
 const (
 	resolutionAlertmanager = "alertmanager"
 	resolutionExpiry       = "expiry"
+
+	// resolutionDeadman marks a heartbeat the dead man's switch sweeper declared
+	// dead. Distinct from expiry because it is load-bearing, not just
+	// descriptive: it is the one resolution the ingest upsert will let a
+	// same-instance re-fire undo, so a switch that comes back can be heard.
+	resolutionDeadman = "deadman"
 )
 
 // amPayload mirrors the Alertmanager webhook v4 payload.
@@ -56,9 +62,15 @@ type ingested struct {
 
 	// justResolved marks the firing → resolved edge, worth a timeline entry.
 	justResolved bool
+
+	// deadman marks a heartbeat: an alert whose arrival means everything is
+	// fine. It is stored like any other alert — received_at is the heartbeat —
+	// but it never reaches an incident. Its absence is what opens one, which
+	// sweepDeadman decides later and elsewhere.
+	deadman bool
 }
 
-func handleAlertmanagerWebhook(db *sql.DB) http.HandlerFunc {
+func handleAlertmanagerWebhook(db *sql.DB, notify NotifyConfig, deadman DeadmanConfig) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		var payload amPayload
 		if err := decodeJSON(r, &payload); err != nil {
@@ -69,7 +81,7 @@ func handleAlertmanagerWebhook(db *sql.DB) http.HandlerFunc {
 		// Alertmanager retries anything that is not 2xx, and a retry of a payload
 		// we failed to store is more useful than an error it cannot act on — so
 		// failures are logged, not surfaced.
-		if err := ingest(r.Context(), db, payload); err != nil {
+		if err := ingest(r.Context(), db, notify, deadman, payload); err != nil {
 			log.Printf("webhook ingest (group %q): %v", payload.GroupKey, err)
 		}
 
@@ -80,14 +92,14 @@ func handleAlertmanagerWebhook(db *sql.DB) http.HandlerFunc {
 // ingest stores a payload's alerts and reconciles the incident for its group.
 // The whole payload is one transaction: an incident that opened but whose alerts
 // failed to link would be a work item nobody could act on.
-func ingest(ctx context.Context, db *sql.DB, payload amPayload) error {
+func ingest(ctx context.Context, db *sql.DB, notify NotifyConfig, deadman DeadmanConfig, payload amPayload) error {
 	tx, err := db.BeginTx(ctx, nil)
 	if err != nil {
 		return err
 	}
 	defer tx.Rollback() //nolint:errcheck
 
-	accepted, err := upsertAlerts(ctx, tx, payload.Alerts)
+	accepted, err := upsertAlerts(ctx, tx, deadman, payload.Alerts)
 	if err != nil {
 		return err
 	}
@@ -96,14 +108,14 @@ func ingest(ctx context.Context, db *sql.DB, payload amPayload) error {
 	// resolution cascade are recomputed once per incident at the end.
 	touched := map[int64]bool{}
 
-	incidentID, err := incidentForGroup(ctx, tx, payload, accepted)
+	incidentID, err := incidentForGroup(ctx, tx, notify, payload, accepted)
 	if err != nil {
 		return err
 	}
 	if incidentID != 0 {
 		touched[incidentID] = true
 		for _, a := range accepted {
-			if !a.firing {
+			if !a.firing || a.deadman {
 				continue
 			}
 			if err := linkAlert(ctx, tx, incidentID, a.id); err != nil {
@@ -113,7 +125,7 @@ func ingest(ctx context.Context, db *sql.DB, payload amPayload) error {
 	}
 
 	for _, a := range accepted {
-		if !a.justResolved {
+		if !a.justResolved || a.deadman {
 			continue
 		}
 		id, err := openIncidentForAlert(ctx, tx, a.id)
@@ -144,7 +156,7 @@ func ingest(ctx context.Context, db *sql.DB, payload amPayload) error {
 
 // upsertAlerts stores each alert of a payload and reports what changed. Payloads
 // the ordering guard rejected are left out entirely.
-func upsertAlerts(ctx context.Context, tx *sql.Tx, alerts []amAlert) ([]ingested, error) {
+func upsertAlerts(ctx context.Context, tx *sql.Tx, deadman DeadmanConfig, alerts []amAlert) ([]ingested, error) {
 	now := time.Now().Unix()
 	accepted := make([]ingested, 0, len(alerts))
 
@@ -187,7 +199,15 @@ func upsertAlerts(ctx context.Context, tx *sql.Tx, alerts []amAlert) ([]ingested
 		// older than the stored one. Alertmanager retries failed notifications,
 		// so a stale firing retry can arrive after the resolved one; it carries
 		// the same startsAt, whereas a genuine re-fire carries a newer one.
-		// Within a single instance, resolution is terminal.
+		// Within a single instance, resolution is terminal — with one exception.
+		//
+		// A resolution this server synthesised for a dead man's switch is not
+		// Alertmanager's word that the instance ended; it is our inference from
+		// silence. The heartbeat that proves us wrong carries the unchanged
+		// startsAt of an alert that never stopped firing, so without the
+		// exemption a switch could go dead exactly once and never be heard from
+		// again. Scoped to 'deadman' so no resolution anybody else wrote can be
+		// undone by a stale retry.
 		if _, err := tx.ExecContext(ctx, `
 			INSERT INTO alerts
 				(fingerprint, name, status, labels, annotations, starts_at, ends_at,
@@ -211,7 +231,8 @@ func upsertAlerts(ctx context.Context, tx *sql.Tx, alerts []amAlert) ([]ingested
 				                        THEN NULL ELSE alerts.archived_at END
 			WHERE excluded.starts_at > alerts.starts_at
 			   OR (excluded.starts_at = alerts.starts_at
-			       AND NOT (alerts.status = 'resolved' AND excluded.status = 'firing'))`,
+			       AND (alerts.resolution_source = '`+resolutionDeadman+`'
+			            OR NOT (alerts.status = 'resolved' AND excluded.status = 'firing')))`,
 			a.Fingerprint, name, a.Status,
 			string(labelsJSON), string(annotationsJSON),
 			a.StartsAt.Unix(), endsAtUnix,
@@ -244,6 +265,7 @@ func upsertAlerts(ctx context.Context, tx *sql.Tx, alerts []amAlert) ([]ingested
 			firing:        firing,
 			newOccurrence: firing && (!existed || a.StartsAt.Unix() > prevStartsAt || prevStatus == "resolved"),
 			justResolved:  !firing && existed && prevStatus == "firing",
+			deadman:       deadman.isDeadman(a.Labels),
 		})
 	}
 
@@ -258,10 +280,17 @@ func upsertAlerts(ctx context.Context, tx *sql.Tx, alerts []amAlert) ([]ingested
 // something actually started firing. Without that, a manually resolved incident
 // would reappear on the next repeat_interval re-send of an alert that never
 // stopped, and manual resolution would be meaningless.
-func incidentForGroup(ctx context.Context, tx *sql.Tx, payload amPayload, accepted []ingested) (int64, error) {
+//
+// Heartbeats do not count as anything here. A group of nothing but dead man's
+// switch alerts opens no incident at all, and a mixed group gets an incident for
+// its real alerts only.
+func incidentForGroup(ctx context.Context, tx *sql.Tx, notify NotifyConfig, payload amPayload, accepted []ingested) (int64, error) {
 	var firstName string
 	anyFiring, anyNew := false, false
 	for _, a := range accepted {
+		if a.deadman {
+			continue
+		}
 		if a.firing {
 			if !anyFiring {
 				firstName = a.name
@@ -297,13 +326,20 @@ func incidentForGroup(ctx context.Context, tx *sql.Tx, payload amPayload, accept
 	if !anyNew {
 		return 0, nil
 	}
-	return openIncident(ctx, tx, groupKey, payload.GroupLabels, firstName)
+	return openIncident(ctx, tx, notify, groupKey,
+		incidentTitle(payload.GroupLabels, firstName), payload.GroupLabels, nil)
 }
 
-// openIncident creates an incident for a group and assigns it to whoever is on
-// call today, which is the point at which the schedule stops being decorative.
-func openIncident(ctx context.Context, tx *sql.Tx, groupKey string, groupLabels map[string]string, fallbackName string) (int64, error) {
-	onCall, err := currentOnCall(ctx, tx)
+// openIncident creates an incident and assigns it to whoever is on call today,
+// which is the point at which the schedule stops being decorative.
+//
+// The one place an incident is born, for both of the things that can raise one:
+// the webhook, inside its transaction, and the dead man's switch sweeper, inside
+// its own. Hence the querier rather than a *sql.Tx. A nil severity leaves the
+// column for refreshSeverity to fill from the member alerts; the sweeper passes
+// one because its incidents have no members to derive it from.
+func openIncident(ctx context.Context, q querier, notify NotifyConfig, groupKey, title string, groupLabels map[string]string, severity *string) (int64, error) {
+	onCall, err := currentOnCall(ctx, q)
 	if err != nil {
 		return 0, err
 	}
@@ -313,10 +349,10 @@ func openIncident(ctx context.Context, tx *sql.Tx, groupKey string, groupLabels
 		labelsJSON = []byte("{}")
 	}
 
-	res, err := tx.ExecContext(ctx, `
-		INSERT INTO incidents (group_key, title, group_labels, status, triggered_at, assigned_to)
-		VALUES (?, ?, ?, 'triggered', ?, ?)`,
-		groupKey, incidentTitle(groupLabels, fallbackName), string(labelsJSON),
+	res, err := q.ExecContext(ctx, `
+		INSERT INTO incidents (group_key, title, group_labels, status, severity, triggered_at, assigned_to)
+		VALUES (?, ?, ?, 'triggered', ?, ?, ?)`,
+		groupKey, title, string(labelsJSON), severity,
 		time.Now().Unix(), onCall)
 	if err != nil {
 		return 0, err
@@ -326,15 +362,22 @@ func openIncident(ctx context.Context, tx *sql.Tx, groupKey string, groupLabels
 		return 0, err
 	}
 
-	if err := logEvent(ctx, tx, id, evTriggered, nil, nil, nil); err != nil {
+	if err := logEvent(ctx, q, id, evTriggered, nil, nil, nil); err != nil {
 		return 0, err
 	}
 	if onCall != nil {
 		// On an "assigned" event user_id is the assignee, not the actor.
-		if err := logEvent(ctx, tx, id, evAssigned, onCall, nil, nil); err != nil {
+		if err := logEvent(ctx, q, id, evAssigned, onCall, nil, nil); err != nil {
 			return 0, err
 		}
 	}
+
+	// Queue the page, but do not send it here: this runs inside a transaction on
+	// a single-connection pool, so an HTTP call would hold up every other
+	// request. The notifier picks the row up within a tick.
+	if err := enqueueOpened(ctx, q, notify, id, onCall); err != nil {
+		return 0, err
+	}
 	return id, nil
 }
 

internal/api/alerts.go

@@ -10,8 +10,8 @@ import (
 	"strings"
 	"time"
 
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 	"github.com/go-chi/chi/v5"
-	"github.com/yeniklas/terdut-server/internal/models"
 )
 
 // alertSelectFrom is the shared SELECT … FROM … clause used by all alert queries.

internal/api/api_test.go

@@ -12,20 +12,40 @@ import (
 	"testing"
 	"time"
 
-	"github.com/yeniklas/terdut-server/internal/api"
-	"github.com/yeniklas/terdut-server/internal/db"
+	"git.ryuvia.com/niklas/terdut-server/internal/api"
+	"git.ryuvia.com/niklas/terdut-server/internal/db"
 )
 
 // ts wraps httptest.Server with a pre-bootstrapped API key. db is exposed so
 // tests can age rows directly — the sweeper's inputs are wall-clock timestamps.
 type ts struct {
 	*httptest.Server
-	key string
-	db  *sql.DB
+	key     string
+	db      *sql.DB
+	notify  api.NotifyConfig
+	deadman api.DeadmanConfig
 }
 
-func newTS(t *testing.T) *ts {
+// newTS builds a server over a fresh in-memory database. Notifications are off
+// unless a NotifyConfig is passed, so tests that predate them are unaffected.
+// Dead man's switches are off too — see newDeadmanTS.
+func newTS(t *testing.T, notify ...api.NotifyConfig) *ts {
 	t.Helper()
+	var cfg api.NotifyConfig
+	if len(notify) > 0 {
+		cfg = notify[0]
+	}
+	return newDeadmanTS(t, api.DeadmanConfig{}, cfg)
+}
+
+// newDeadmanTS is newTS with dead man's switch handling configured.
+func newDeadmanTS(t *testing.T, deadman api.DeadmanConfig, notify ...api.NotifyConfig) *ts {
+	t.Helper()
+	var cfg api.NotifyConfig
+	if len(notify) > 0 {
+		cfg = notify[0]
+	}
+
 	database, err := db.Open(":memory:")
 	if err != nil {
 		t.Fatalf("open db: %v", err)
@@ -33,7 +53,7 @@ func newTS(t *testing.T) *ts {
 	if err := db.Migrate(database); err != nil {
 		t.Fatalf("migrate: %v", err)
 	}
-	srv := httptest.NewServer(api.NewRouter(database))
+	srv := httptest.NewServer(api.NewRouter(database, cfg, deadman))
 	t.Cleanup(func() { srv.Close(); database.Close() })
 
 	body, _ := json.Marshal(map[string]string{"username": "admin", "email": "admin@test.com"})
@@ -49,7 +69,7 @@ func newTS(t *testing.T) *ts {
 	json.NewDecoder(resp.Body).Decode(&result)
 	key := result["api_key"].(map[string]any)["key"].(string)
 
-	return &ts{Server: srv, key: key, db: database}
+	return &ts{Server: srv, key: key, db: database, notify: cfg, deadman: deadman}
 }
 
 // exec runs a statement against the test database.
@@ -302,6 +322,125 @@ func TestSchedule_MultiDateRollbackOnConflict(t *testing.T) {
 	}
 }
 
+// ---------------------------------------------------------------------------
+// Schedule reassignment
+// ---------------------------------------------------------------------------
+
+// addUser creates a second person to hand a shift to. The bootstrap user is
+// admin, id 1.
+func addUser(t *testing.T, s *ts, username string) {
+	t.Helper()
+	resp := s.req(t, http.MethodPost, "/api/users",
+		map[string]any{"username": username, "email": username + "@test.com"})
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("create user returned %d", resp.StatusCode)
+	}
+}
+
+// scheduleHolder reports who is on call for one date, or "" for nobody.
+func scheduleHolder(t *testing.T, s *ts, date string) string {
+	t.Helper()
+	var entries []map[string]any
+	decode(t, s.req(t, http.MethodGet, "/api/schedule?from="+date+"&to="+date, nil), &entries)
+	if len(entries) == 0 {
+		return ""
+	}
+	return entries[0]["username"].(string)
+}
+
+// Taking a day somebody else holds is possible, but only by asking for it.
+func TestSchedule_ReplaceTakesAnAssignedDate(t *testing.T) {
+	s := newTS(t)
+	addUser(t, s, "alex")
+
+	s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 1, "dates": []string{"2026-06-01"}}).Body.Close()
+
+	resp := s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 2, "dates": []string{"2026-06-01"}, "replace": true})
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("expected replace to succeed, got %d", resp.StatusCode)
+	}
+	resp.Body.Close()
+
+	if got := scheduleHolder(t, s, "2026-06-01"); got != "alex" {
+		t.Errorf("expected alex to hold the day, got %q", got)
+	}
+
+	// One row, not two: two entries for a date would mean two people believing
+	// they are on call for it.
+	var entries []map[string]any
+	decode(t, s.req(t, http.MethodGet, "/api/schedule?from=2026-06-01&to=2026-06-01", nil), &entries)
+	if len(entries) != 1 {
+		t.Errorf("expected exactly one entry for the date, got %d", len(entries))
+	}
+}
+
+// A week where only some days are taken is the case that was impossible before:
+// the free days and the taken ones have to land together.
+func TestSchedule_ReplaceMixedWeek(t *testing.T) {
+	s := newTS(t)
+	addUser(t, s, "alex")
+
+	s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 1, "dates": []string{"2026-06-02", "2026-06-04"}}).Body.Close()
+
+	week := []string{"2026-06-01", "2026-06-02", "2026-06-03", "2026-06-04", "2026-06-05"}
+	resp := s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 2, "dates": week, "replace": true})
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("expected the mixed week to succeed, got %d", resp.StatusCode)
+	}
+	resp.Body.Close()
+
+	for _, d := range week {
+		if got := scheduleHolder(t, s, d); got != "alex" {
+			t.Errorf("%s: expected alex, got %q", d, got)
+		}
+	}
+}
+
+// Without replace the guard stands: nobody loses a shift by accident.
+func TestSchedule_ReplaceDefaultsOff(t *testing.T) {
+	s := newTS(t)
+	addUser(t, s, "alex")
+
+	s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 1, "dates": []string{"2026-06-01"}}).Body.Close()
+
+	resp := s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 2, "dates": []string{"2026-06-01"}})
+	if resp.StatusCode != http.StatusConflict {
+		t.Fatalf("expected 409 without replace, got %d", resp.StatusCode)
+	}
+	resp.Body.Close()
+
+	if got := scheduleHolder(t, s, "2026-06-01"); got != "admin" {
+		t.Errorf("expected the original holder untouched, got %q", got)
+	}
+}
+
+// Replace makes a repeated date idempotent rather than a conflict: the second
+// pass clears what the first wrote and rewrites it. Worth pinning down, because
+// the same input without replace is a 409.
+func TestSchedule_ReplaceCollapsesRepeatedDates(t *testing.T) {
+	s := newTS(t)
+
+	resp := s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": 1, "dates": []string{"2026-06-01", "2026-06-01"}, "replace": true})
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("expected a repeated date to be accepted under replace, got %d", resp.StatusCode)
+	}
+	resp.Body.Close()
+
+	var entries []map[string]any
+	decode(t, s.req(t, http.MethodGet, "/api/schedule?from=2026-06-01&to=2026-06-01", nil), &entries)
+	if len(entries) != 1 {
+		t.Errorf("expected one entry for the repeated date, got %d", len(entries))
+	}
+}
+
 // ---------------------------------------------------------------------------
 // Stats
 // ---------------------------------------------------------------------------
@@ -366,7 +505,7 @@ func TestArchive_AlertListFilter(t *testing.T) {
 	}
 
 	// 2. Let the sweeper archive it: ends_at is already well past archiveAfter.
-	api.Sweep(context.Background(), s.db, time.Hour, 6*time.Hour)
+	api.Sweep(context.Background(), s.db, time.Hour, 6*time.Hour, s.deadman, s.notify)
 
 	// 3. Default list excludes it.
 	decode(t, s.req(t, http.MethodGet, "/api/alerts", nil), &alerts)
@@ -407,7 +546,7 @@ func postAlert(t *testing.T, s *ts, fingerprint, status, startsAt, endsAt string
 
 func sweep(t *testing.T, s *ts, staleAfter time.Duration) {
 	t.Helper()
-	api.Sweep(context.Background(), s.db, noArchive, staleAfter)
+	api.Sweep(context.Background(), s.db, noArchive, staleAfter, s.deadman, s.notify)
 }
 
 // A firing alert Alertmanager stopped refreshing is resolved via the

internal/api/archiver.go

@@ -19,31 +19,38 @@ const (
 
 // StartArchiver runs the alert sweeper until ctx is cancelled, starting with an
 // immediate pass so a restart reconciles state right away.
-func StartArchiver(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Duration) {
+func StartArchiver(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Duration, deadman DeadmanConfig, notify NotifyConfig) {
 	ticker := time.NewTicker(sweepInterval)
 	defer ticker.Stop()
 
-	Sweep(ctx, db, archiveAfter, staleAfter)
+	Sweep(ctx, db, archiveAfter, staleAfter, deadman, notify)
 	for {
 		select {
 		case <-ticker.C:
-			Sweep(ctx, db, archiveAfter, staleAfter)
+			Sweep(ctx, db, archiveAfter, staleAfter, deadman, notify)
 		case <-ctx.Done():
 			return
 		}
 	}
 }
 
-// Sweep runs a single pass, in dependency order: expire stale firing alerts,
-// close the incidents that leaves with nothing firing, then archive whatever has
-// been settled long enough. Running them in one pass means an alert can go stale
-// and its incident can close and archive without waiting three ticks.
+// Sweep runs a single pass, in dependency order: reconcile the dead man's
+// switches, expire stale firing alerts, close the incidents that leaves with
+// nothing firing, then archive whatever has been settled long enough. Running
+// them in one pass means an alert can go stale and its incident can close and
+// archive without waiting three ticks.
+//
+// The switches go first because they hand expireStale the alerts it must not
+// touch: a heartbeat answers to its own, much tighter, timeout, and the generic
+// staleness rules would otherwise resolve it as 'expiry' long before that.
 // Exported so tests can drive a pass without waiting on the ticker.
-func Sweep(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Duration) {
-	expireStale(ctx, db, staleAfter)
+func Sweep(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Duration, deadman DeadmanConfig, notify NotifyConfig) {
+	heartbeats := sweepDeadman(ctx, db, deadman, notify)
+	expireStale(ctx, db, staleAfter, heartbeats)
 	resolveSettledIncidents(ctx, db)
 	archiveResolved(ctx, db, archiveAfter)
 	archiveResolvedIncidents(ctx, db, archiveAfter)
+	purgeAckTokens(ctx, db)
 }
 
 // expireStale resolves firing alerts that Alertmanager has stopped refreshing.
@@ -59,16 +66,26 @@ func Sweep(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Durati
 //     notifications every repeat_interval, making received_at a liveness
 //     heartbeat — provided staleAfter exceeds that interval.
 //
+// Alerts in skip are left alone: they are dead man's switch heartbeats, whose
+// liveness sweepDeadman has already judged against a timeout of its own.
+//
 // The matching rows are collected before the update rather than updated in bulk,
 // because each one owes its incident a timeline entry.
-func expireStale(ctx context.Context, db *sql.DB, staleAfter time.Duration) {
+func expireStale(ctx context.Context, db *sql.DB, staleAfter time.Duration, skip map[int64]bool) {
 	now := time.Now()
 
-	ids, err := staleAlertIDs(ctx, db, now, staleAfter)
+	found, err := staleAlertIDs(ctx, db, now, staleAfter)
 	if err != nil {
 		log.Printf("sweeper: find stale: %v", err)
 		return
 	}
+
+	ids := make([]int64, 0, len(found))
+	for _, id := range found {
+		if !skip[id] {
+			ids = append(ids, id)
+		}
+	}
 	if len(ids) == 0 {
 		return
 	}

internal/api/deadman.go

@@ -0,0 +1,378 @@
+package api
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"log"
+	"sort"
+	"strings"
+	"time"
+)
+
+// deadmanGroupPrefix namespaces the incidents this file opens. Alertmanager
+// group keys always contain braces, so this can never collide with one, and the
+// partial unique index on open group_key (see 008_incidents.sql) gives one open
+// incident per switch for free.
+const deadmanGroupPrefix = "deadman:"
+
+// DeadmanMatcher selects the alerts that are heartbeats rather than problems.
+// Every condition has to match, and Name — the alertname label — is mandatory:
+// it is what lets the sweeper find candidate rows through alerts_name_idx
+// instead of JSON-extracting labels from every row in the table.
+type DeadmanMatcher struct {
+	Name   string
+	Labels map[string]string
+}
+
+// String renders the matcher the way it was configured, which is also how it
+// reads in an incident title.
+func (m DeadmanMatcher) String() string {
+	if len(m.Labels) == 0 {
+		return m.Name
+	}
+	parts := make([]string, 0, len(m.Labels))
+	for k, v := range m.Labels {
+		parts = append(parts, k+"="+v)
+	}
+	sort.Strings(parts)
+	return m.Name + " (" + strings.Join(parts, ", ") + ")"
+}
+
+// matches reports whether an alert's labels satisfy every condition.
+func (m DeadmanMatcher) matches(labels map[string]string) bool {
+	if labels["alertname"] != m.Name {
+		return false
+	}
+	for k, v := range m.Labels {
+		if labels[k] != v {
+			return false
+		}
+	}
+	return true
+}
+
+// DeadmanConfig inverts the handling of the alerts it matches: receiving one
+// opens nothing, and the absence of one opens an incident.
+//
+// The unit of monitoring is the fingerprint, not the matcher — two clusters
+// sending the same heartbeat alertname are two independent switches, so one
+// healthy cluster cannot mask a dead one.
+type DeadmanConfig struct {
+	Matchers []DeadmanMatcher
+
+	// Timeout is how long a matched alert may go without a refreshing webhook
+	// before it is declared dead. It must be shorter than Alertmanager's
+	// repeat_interval for the heartbeat's route, which is what refreshes it.
+	// Zero disables dead man's switch handling entirely.
+	Timeout time.Duration
+
+	// Severity is the severity every dead man's switch incident opens at. These
+	// incidents have no member alerts to derive one from, and the heartbeat's
+	// own severity label is meaningless — Watchdog ships as "none".
+	Severity string
+}
+
+// enabled reports whether there is anything to watch.
+func (c DeadmanConfig) enabled() bool { return c.Timeout > 0 && len(c.Matchers) > 0 }
+
+// match returns the first matcher an alert satisfies.
+func (c DeadmanConfig) match(labels map[string]string) (DeadmanMatcher, bool) {
+	if !c.enabled() {
+		return DeadmanMatcher{}, false
+	}
+	for _, m := range c.Matchers {
+		if m.matches(labels) {
+			return m, true
+		}
+	}
+	return DeadmanMatcher{}, false
+}
+
+// isDeadman is match without the matcher, for the ingest path.
+func (c DeadmanConfig) isDeadman(labels map[string]string) bool {
+	_, ok := c.match(labels)
+	return ok
+}
+
+// names lists the distinct alertnames worth loading from the database.
+func (c DeadmanConfig) names() []string {
+	seen := map[string]bool{}
+	out := make([]string, 0, len(c.Matchers))
+	for _, m := range c.Matchers {
+		if !seen[m.Name] {
+			seen[m.Name] = true
+			out = append(out, m.Name)
+		}
+	}
+	return out
+}
+
+// ParseDeadmanConfig reads the matcher list from its configured form:
+// ";" separates matchers, "," separates the conditions within one, and "=" is
+// exact label equality — `alertname=Watchdog,cluster=prod; alertname=Heartbeat`.
+//
+// A malformed or alertname-less entry is dropped rather than fatal, following
+// config.duration's rule that one bad tuning knob should not take the server
+// down. Silence would be worse here than elsewhere, though — a typo that
+// disarms the switch is exactly the failure this feature exists to catch — so
+// the matchers that survived are logged.
+func ParseDeadmanConfig(matchers string, timeout time.Duration, severity string) DeadmanConfig {
+	cfg := DeadmanConfig{Timeout: timeout, Severity: severity}
+
+	for _, entry := range strings.Split(matchers, ";") {
+		entry = strings.TrimSpace(entry)
+		if entry == "" {
+			continue
+		}
+
+		m := DeadmanMatcher{Labels: map[string]string{}}
+		malformed := false
+		for _, cond := range strings.Split(entry, ",") {
+			k, v, ok := strings.Cut(cond, "=")
+			k, v = strings.TrimSpace(k), strings.TrimSpace(v)
+			if !ok || k == "" || v == "" {
+				log.Printf("deadman: ignoring matcher %q: %q is not label=value", entry, strings.TrimSpace(cond))
+				malformed = true
+				break
+			}
+			if k == "alertname" {
+				m.Name = v
+				continue
+			}
+			m.Labels[k] = v
+		}
+		if malformed {
+			continue
+		}
+		if m.Name == "" {
+			log.Printf("deadman: ignoring matcher %q: no alertname condition", entry)
+			continue
+		}
+		cfg.Matchers = append(cfg.Matchers, m)
+	}
+
+	switch {
+	case timeout <= 0:
+		log.Print("deadman: disabled (timeout is zero)")
+	case len(cfg.Matchers) == 0:
+		log.Print("deadman: disabled (no usable matchers)")
+	default:
+		rendered := make([]string, 0, len(cfg.Matchers))
+		for _, m := range cfg.Matchers {
+			rendered = append(rendered, m.String())
+		}
+		log.Printf("deadman: watching %s, timeout %s, severity %s",
+			strings.Join(rendered, "; "), timeout, severity)
+	}
+	return cfg
+}
+
+// deadmanAlert is one switch: the alert row carrying its last heartbeat.
+type deadmanAlert struct {
+	id          int64
+	fingerprint string
+	labels      map[string]string
+	matcher     DeadmanMatcher
+	resolved    bool
+	receivedAt  int64
+}
+
+// groupKey is the switch's identity as an incident. Per fingerprint, so each
+// source is tracked on its own.
+func (a deadmanAlert) groupKey() string { return deadmanGroupPrefix + a.fingerprint }
+
+// sweepDeadman is the whole point of the feature: it opens an incident for every
+// switch that has stopped chirping, and closes one whose switch came back.
+//
+// It returns the ids of the alerts it owns, because the generic staleness
+// expiry must leave them alone — staleAfter and ends_at would otherwise resolve
+// a heartbeat long before its own, much tighter, timeout ever fired.
+func sweepDeadman(ctx context.Context, db *sql.DB, cfg DeadmanConfig, notify NotifyConfig) map[int64]bool {
+	owned := map[int64]bool{}
+	if !cfg.enabled() {
+		return owned
+	}
+
+	switches, err := deadmanAlerts(ctx, db, cfg)
+	if err != nil {
+		log.Printf("deadman: load switches: %v", err)
+		return owned
+	}
+
+	now := time.Now()
+	cutoff := now.Add(-cfg.Timeout).Unix()
+
+	for _, sw := range switches {
+		owned[sw.id] = true
+
+		// An explicit resolved from Alertmanager is a stronger death signal than
+		// mere absence: the sender is telling us the heartbeat stopped, so there
+		// is nothing left to wait out.
+		if sw.resolved || sw.receivedAt < cutoff {
+			if err := deadmanDied(ctx, db, cfg, notify, sw, now); err != nil {
+				log.Printf("deadman: open incident for %s: %v", sw.matcher.Name, err)
+			}
+			continue
+		}
+		if err := deadmanRecovered(ctx, db, sw); err != nil {
+			log.Printf("deadman: resolve incident for %s: %v", sw.matcher.Name, err)
+		}
+	}
+	return owned
+}
+
+// deadmanAlerts loads every alert row that a matcher claims. The candidate query
+// is narrowed by alertname so it rides alerts_name_idx; the rest of the matching
+// happens in Go, which keeps one implementation of the rules. The rows are read
+// in full before the caller writes, because the pool holds a single connection.
+func deadmanAlerts(ctx context.Context, db *sql.DB, cfg DeadmanConfig) ([]deadmanAlert, error) {
+	names := cfg.names()
+	args := make([]any, 0, len(names))
+	for _, n := range names {
+		args = append(args, n)
+	}
+
+	rows, err := db.QueryContext(ctx, `
+		SELECT id, fingerprint, labels, status, received_at
+		FROM   alerts
+		WHERE  name IN (`+placeholders(len(names))+`)
+		  AND  archived_at IS NULL`, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []deadmanAlert
+	for rows.Next() {
+		var a deadmanAlert
+		var labelsJSON, status string
+		if err := rows.Scan(&a.id, &a.fingerprint, &labelsJSON, &status, &a.receivedAt); err != nil {
+			return nil, err
+		}
+		json.Unmarshal([]byte(labelsJSON), &a.labels) //nolint:errcheck
+
+		m, ok := cfg.match(a.labels)
+		if !ok {
+			continue
+		}
+		a.matcher = m
+		a.resolved = status == "resolved"
+		out = append(out, a)
+	}
+	return out, rows.Err()
+}
+
+// deadmanDied raises the incident for a switch that has gone quiet.
+//
+// Two conditions gate it, and both matter. There must be no open incident for
+// the switch already — the partial unique index enforces that anyway, but a
+// second one would be a wasted page. And the heartbeat must have been seen since
+// the last incident was raised, which is the re-arm rule: resolving a dead man's
+// switch incident sticks, exactly as resolving an alert-backed one does (see
+// incidentForGroup), and a source that is gone for good is a one-time page
+// rather than a nag. Only a heartbeat that comes back and dies again earns a new
+// incident.
+func deadmanDied(ctx context.Context, db *sql.DB, cfg DeadmanConfig, notify NotifyConfig, sw deadmanAlert, now time.Time) error {
+	var lastTriggered, open int64
+	if err := db.QueryRowContext(ctx, `
+		SELECT COALESCE(MAX(triggered_at), 0),
+		       COALESCE(SUM(resolved_at IS NULL), 0)
+		FROM   incidents WHERE group_key = ?`,
+		sw.groupKey()).Scan(&lastTriggered, &open); err != nil {
+		return err
+	}
+	if open > 0 || sw.receivedAt <= lastTriggered {
+		return nil
+	}
+
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+	// A heartbeat nobody has heard from is not firing, and saying otherwise in
+	// the alert list would be a lie. An Alertmanager-sourced resolution keeps its
+	// own source: it told us the truth first.
+	if !sw.resolved {
+		if _, err := tx.ExecContext(ctx, `
+			UPDATE alerts
+			   SET status            = 'resolved',
+			       resolution_source = ?,
+			       ends_at           = COALESCE(ends_at, unixepoch())
+			 WHERE id = ? AND status = 'firing'`, resolutionDeadman, sw.id); err != nil {
+			return err
+		}
+	}
+
+	severity := cfg.Severity
+	var sev *string
+	if severity != "" {
+		sev = &severity
+	}
+
+	incidentID, err := openIncident(ctx, tx, notify, sw.groupKey(),
+		"No heartbeat from "+sw.matcher.String(), sw.labels, sev)
+	if err != nil {
+		return err
+	}
+
+	alertID := sw.id
+	detail := "last heartbeat " + humanDuration(now.Sub(time.Unix(sw.receivedAt, 0))) + " ago"
+	if err := logEvent(ctx, tx, incidentID, evDeadmanSilent, nil, &alertID, &detail); err != nil {
+		return err
+	}
+
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	log.Printf("deadman: %s went silent, opened incident %d", sw.matcher.String(), incidentID)
+	return nil
+}
+
+// deadmanRecovered closes the incident for a switch that started chirping again.
+//
+// It cannot go through resolveIfSettled: a dead man's switch incident has no
+// member alerts (linking the heartbeat would have the settled-incident cascade
+// close it on the very same sweep that opened it), so the alert-driven cascade
+// ignores it entirely and recovery is the only automatic way out.
+func deadmanRecovered(ctx context.Context, db *sql.DB, sw deadmanAlert) error {
+	var incidentID int64
+	switch err := db.QueryRowContext(ctx, `
+		SELECT id FROM incidents
+		 WHERE group_key = ? AND resolved_at IS NULL`, sw.groupKey()).Scan(&incidentID); {
+	case err == sql.ErrNoRows:
+		return nil
+	case err != nil:
+		return err
+	}
+
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+	if _, err := tx.ExecContext(ctx, `
+		UPDATE incidents
+		   SET status = 'resolved', resolved_at = ?, resolution_source = ?
+		 WHERE id = ? AND resolved_at IS NULL`,
+		time.Now().Unix(), incidentResolutionRecovered, incidentID); err != nil {
+		return err
+	}
+	if err := logEvent(ctx, tx, incidentID, evResolved, nil, nil, nil); err != nil {
+		return err
+	}
+	// The all-clear goes to whoever was paged, which enqueueResolved works out
+	// from the incident's own notification history.
+	if err := enqueueResolved(ctx, tx, incidentID); err != nil {
+		return err
+	}
+
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	log.Printf("deadman: %s is back, resolved incident %d", sw.matcher.String(), incidentID)
+	return nil
+}

internal/api/deadman_test.go

@@ -0,0 +1,468 @@
+package api_test
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	"git.ryuvia.com/niklas/terdut-server/internal/api"
+)
+
+// ---------------------------------------------------------------------------
+// Harness
+// ---------------------------------------------------------------------------
+
+// watchdogGroupKey is what Alertmanager sends for a Watchdog grouped by
+// alertname, which is how the deployed route is configured.
+const watchdogGroupKey = `{}:{alertname="Watchdog"}`
+
+// deadmanCfg watches Watchdog with a timeout short enough to reason about and
+// long enough that a fresh heartbeat is never accidentally stale.
+func deadmanCfg() api.DeadmanConfig {
+	return api.ParseDeadmanConfig("alertname=Watchdog", time.Hour, "critical")
+}
+
+// deadmanTS is notifyTS with dead man's switch handling on: notifications
+// enabled against a fake ntfy, the admin on call today with a topic.
+func deadmanTS(t *testing.T, cfg api.DeadmanConfig) (*ts, *fakeNtfy) {
+	t.Helper()
+	f := newFakeNtfy(t)
+	s := newDeadmanTS(t, cfg, api.NotifyConfig{
+		BaseURL:   f.URL,
+		PublicURL: "https://terdut.example.com",
+	})
+
+	putOnCall(t, s, 1)
+	setTopic(t, s, 1, "terdut-admin")
+	return s, f
+}
+
+// heartbeat posts one Watchdog webhook. Its startsAt never changes: a dead man's
+// switch alert fires once and is re-sent unchanged forever, which is precisely
+// what makes its absence meaningful.
+func heartbeat(t *testing.T, s *ts, fingerprint string, labels map[string]string) {
+	t.Helper()
+	postWebhook(t, s, []map[string]any{
+		amAlert(fingerprint, "Watchdog", "firing", "2026-05-20T10:00:00Z", zeroTime, labels),
+	}, watchdogGroupKey)
+}
+
+// silence back-dates a heartbeat's received_at, which is the only clock the
+// sweeper reads. There is no fake clock in this package.
+func silence(t *testing.T, s *ts, fingerprint string, ago time.Duration) {
+	t.Helper()
+	s.exec(t, "UPDATE alerts SET received_at = ? WHERE fingerprint = ?",
+		time.Now().Add(-ago).Unix(), fingerprint)
+}
+
+// ageIncidents back-dates every incident. The re-arm rule compares a heartbeat
+// against the last incident raised for its switch, so a test that wants a second
+// episode has to put the first one in the past — there is no fake clock here.
+func ageIncidents(t *testing.T, s *ts, ago time.Duration) {
+	t.Helper()
+	past := time.Now().Add(-ago).Unix()
+	s.exec(t, `UPDATE incidents
+	              SET triggered_at = ?,
+	                  resolved_at  = CASE WHEN resolved_at IS NULL THEN NULL ELSE ? END`,
+		past, past)
+}
+
+// incidentByGroup reads the incident for a group key, resolved ones included.
+func incidentByGroup(t *testing.T, s *ts, groupKey string) (id int64, status, severity string, source *string) {
+	t.Helper()
+	err := s.db.QueryRow(`
+		SELECT id, status, COALESCE(severity, ''), resolution_source
+		FROM   incidents WHERE group_key = ? ORDER BY id DESC LIMIT 1`,
+		groupKey).Scan(&id, &status, &severity, &source)
+	if err != nil {
+		t.Fatalf("read incident for group %s: %v", groupKey, err)
+	}
+	return id, status, severity, source
+}
+
+// ---------------------------------------------------------------------------
+// Receiving a heartbeat
+// ---------------------------------------------------------------------------
+
+// The whole inversion: arrival of a dead man's switch alert is good news, and
+// good news is not an incident.
+func TestDeadman_HeartbeatOpensNoIncident(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+
+	if got := s.countIncidents(t); got != 0 {
+		t.Fatalf("expected a heartbeat to open no incident, got %d", got)
+	}
+	if got := s.countNotifications(t, ""); got != 0 {
+		t.Errorf("expected no notification for a heartbeat, got %d", got)
+	}
+	if status, _, _ := s.alertRow(t, "fp-watchdog"); status != "firing" {
+		t.Errorf("expected the heartbeat to be stored firing, got %q", status)
+	}
+}
+
+// A heartbeat routed into a group alongside real alerts must not join their
+// incident: it is not a symptom of anything.
+func TestDeadman_MixedGroupExcludesHeartbeat(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-mixed-wd", "Watchdog", "firing", "2026-05-20T10:00:00Z", zeroTime, nil),
+		amAlert("fp-mixed-disk", "DiskFull", "firing", "2026-05-20T10:00:00Z", zeroTime,
+			map[string]string{"severity": "critical"}),
+	}, `{}:{namespace="prod"}`)
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected 1 incident for the real alert, got %d", got)
+	}
+
+	var alerts []map[string]any
+	decode(t, s.req(t, http.MethodGet, "/api/incidents/1/alerts", nil), &alerts)
+	if len(alerts) != 1 {
+		t.Fatalf("expected 1 member alert, got %d", len(alerts))
+	}
+	if name := alerts[0]["name"]; name != "DiskFull" {
+		t.Errorf("expected only the real alert linked, got %v", name)
+	}
+}
+
+// A matcher scoped by label only claims the alerts it names, so a heartbeat from
+// somewhere else stays an ordinary alert.
+func TestDeadman_LabelScopedMatcherIgnoresOthers(t *testing.T) {
+	s, _ := deadmanTS(t, api.ParseDeadmanConfig("alertname=Watchdog,cluster=prod", time.Hour, "critical"))
+
+	heartbeat(t, s, "fp-dev", map[string]string{"cluster": "dev"})
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected an unmatched Watchdog to behave like any other alert, got %d incidents", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Silence
+// ---------------------------------------------------------------------------
+
+func TestDeadman_SilenceOpensIncident(t *testing.T) {
+	s, f := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected silence to open 1 incident, got %d", got)
+	}
+	id, status, severity, _ := incidentByGroup(t, s, "deadman:fp-watchdog")
+	if status != "triggered" {
+		t.Errorf("expected a triggered incident, got %q", status)
+	}
+	if severity != "critical" {
+		t.Errorf("expected the configured severity, got %q", severity)
+	}
+
+	// The alert list must not keep claiming a dead heartbeat is firing.
+	alertStatus, source, _ := s.alertRow(t, "fp-watchdog")
+	if alertStatus != "resolved" || source == nil || *source != "deadman" {
+		t.Errorf("expected the heartbeat resolved as deadman, got %q / %v", alertStatus, source)
+	}
+
+	// Nobody was told anything by an alert here, so the page has to come from
+	// the switch itself.
+	s.sweepNotify(t)
+	msgs := f.messages()
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 page, got %d", len(msgs))
+	}
+	if msgs[0].Topic != "terdut-admin" {
+		t.Errorf("expected the on-call topic, got %q", msgs[0].Topic)
+	}
+	if msgs[0].Priority != 5 {
+		t.Errorf("expected a critical page to override quiet hours (priority 5), got %d", msgs[0].Priority)
+	}
+
+	// The timeline says why, with the age of the last heartbeat.
+	types := eventTypes(timeline(t, s, int(id)))
+	found := false
+	for _, ty := range types {
+		if ty == "deadman_silent" {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("expected a deadman_silent event, got %v", types)
+	}
+}
+
+// The generic staleness sweep must keep its hands off heartbeats: they answer to
+// their own, much tighter, timeout, and an 'expiry' resolution here would be
+// both wrong and unrecoverable.
+func TestDeadman_GenericExpiryLeavesHeartbeatAlone(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 5*time.Minute)
+
+	// staleAfter far tighter than the dead man's switch timeout.
+	sweep(t, s, time.Minute)
+
+	status, source, _ := s.alertRow(t, "fp-watchdog")
+	if status != "firing" || source != nil {
+		t.Errorf("expected a live heartbeat left alone, got %q / %v", status, source)
+	}
+	if got := s.countIncidents(t); got != 0 {
+		t.Errorf("expected no incident for a heartbeat that is still fresh, got %d", got)
+	}
+}
+
+// An explicit resolved from Alertmanager is the sender telling us the heartbeat
+// stopped. There is nothing left to wait out.
+func TestDeadman_AlertmanagerResolvedIsImmediateDeath(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-watchdog", "Watchdog", "resolved", "2026-05-20T10:00:00Z", zeroTime, nil),
+	}, watchdogGroupKey)
+
+	// No ageing: received_at is seconds old, well inside the timeout.
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected a resolved heartbeat to open an incident at once, got %d", got)
+	}
+	// Alertmanager told the truth first, so its resolution source stands.
+	if _, source, _ := s.alertRow(t, "fp-watchdog"); source == nil || *source != "alertmanager" {
+		t.Errorf("expected the Alertmanager resolution source kept, got %v", source)
+	}
+}
+
+// Each label set is its own switch, so one healthy source cannot mask a dead one.
+func TestDeadman_TracksEachFingerprintSeparately(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-a", map[string]string{"cluster": "a"})
+	heartbeat(t, s, "fp-b", map[string]string{"cluster": "b"})
+	silence(t, s, "fp-b", 2*time.Hour)
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected only the silent switch to page, got %d incidents", got)
+	}
+	if _, status, _, _ := incidentByGroup(t, s, "deadman:fp-b"); status != "triggered" {
+		t.Errorf("expected the incident to belong to the silent switch, got %q", status)
+	}
+	if status, _, _ := s.alertRow(t, "fp-a"); status != "firing" {
+		t.Errorf("expected the live switch untouched, got %q", status)
+	}
+}
+
+// A switch nothing has ever been heard from is dormant. A fresh deploy, a
+// restored database or a typo'd alertname must not page.
+func TestDeadman_UnheardOfSwitchIsDormant(t *testing.T) {
+	s, _ := deadmanTS(t, api.ParseDeadmanConfig("alertname=NeverSent", time.Hour, "critical"))
+
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 0 {
+		t.Fatalf("expected a switch that never chirped to be dormant, got %d incidents", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Recovery and re-arming
+// ---------------------------------------------------------------------------
+
+// The returning heartbeat carries the unchanged startsAt of an alert that never
+// stopped firing, so this also covers the ingest guard exemption: without it the
+// upsert would discard the payload and the switch could die exactly once.
+func TestDeadman_RecoveryResolvesIncident(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	if status, source, _ := s.alertRow(t, "fp-watchdog"); status != "firing" || source != nil {
+		t.Fatalf("expected the returning heartbeat to be accepted, got %q / %v", status, source)
+	}
+
+	sweep(t, s, noArchive)
+
+	_, status, _, source := incidentByGroup(t, s, "deadman:fp-watchdog")
+	if status != "resolved" {
+		t.Errorf("expected recovery to close the incident, got %q", status)
+	}
+	if source == nil || *source != "recovered" {
+		t.Errorf("expected resolution_source recovered, got %v", source)
+	}
+	if got := s.countNotifications(t, "resolved"); got != 1 {
+		t.Errorf("expected 1 all-clear, got %d", got)
+	}
+}
+
+// Resolving a dead man's switch incident sticks, exactly as it does for an
+// alert-backed one. A source that is gone for good is a one-time page.
+func TestDeadman_ManualResolveSticksWhileSilent(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+
+	s.req(t, http.MethodPost, "/api/incidents/1/resolve", nil).Body.Close()
+
+	// Still silent, several sweeps later.
+	sweep(t, s, noArchive)
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected a manually resolved incident to stay closed, got %d", got)
+	}
+}
+
+// ...but the switch re-arms, so a heartbeat that comes back and dies again is a
+// new incident rather than silence forever.
+func TestDeadman_ReArmsAfterHeartbeatReturns(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+	s.req(t, http.MethodPost, "/api/incidents/1/resolve", nil).Body.Close()
+
+	// That episode is yesterday's news; the heartbeat now returns after it.
+	ageIncidents(t, s, 10*time.Hour)
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	sweep(t, s, noArchive)
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected the live switch to open nothing, got %d incidents", got)
+	}
+
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+
+	if got := s.countIncidents(t); got != 2 {
+		t.Fatalf("expected a second death to open a second incident, got %d", got)
+	}
+}
+
+// A dead man's switch incident has no member alerts — linking the heartbeat
+// would have the settled-incident cascade close it on the very sweep that opened
+// it — so the cascade has to leave it alone.
+func TestDeadman_SettledCascadeLeavesIncidentOpen(t *testing.T) {
+	s, _ := deadmanTS(t, deadmanCfg())
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 2*time.Hour)
+	sweep(t, s, noArchive)
+	sweep(t, s, noArchive)
+
+	if _, status, _, _ := incidentByGroup(t, s, "deadman:fp-watchdog"); status != "triggered" {
+		t.Fatalf("expected the incident to stay open until the switch recovers, got %q", status)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Configuration
+// ---------------------------------------------------------------------------
+
+func TestParseDeadmanConfig(t *testing.T) {
+	tests := []struct {
+		name     string
+		matchers string
+		timeout  time.Duration
+		want     []api.DeadmanMatcher
+		enabled  bool
+	}{
+		{
+			name:     "single alertname",
+			matchers: "alertname=Watchdog",
+			timeout:  time.Hour,
+			want:     []api.DeadmanMatcher{{Name: "Watchdog", Labels: map[string]string{}}},
+			enabled:  true,
+		},
+		{
+			name:     "several matchers with extra labels and whitespace",
+			matchers: " alertname=Watchdog, cluster=prod ; alertname=EdgeHeartbeat ",
+			timeout:  time.Hour,
+			want: []api.DeadmanMatcher{
+				{Name: "Watchdog", Labels: map[string]string{"cluster": "prod"}},
+				{Name: "EdgeHeartbeat", Labels: map[string]string{}},
+			},
+			enabled: true,
+		},
+		{
+			// Mandatory: it is what keeps the sweeper's candidate query on an index.
+			name:     "matcher without alertname is dropped",
+			matchers: "cluster=prod; alertname=Watchdog",
+			timeout:  time.Hour,
+			want:     []api.DeadmanMatcher{{Name: "Watchdog", Labels: map[string]string{}}},
+			enabled:  true,
+		},
+		{
+			name:     "malformed condition drops only its matcher",
+			matchers: "alertname=Watchdog,garbage; alertname=Other",
+			timeout:  time.Hour,
+			want:     []api.DeadmanMatcher{{Name: "Other", Labels: map[string]string{}}},
+			enabled:  true,
+		},
+		{
+			name:     "zero timeout disables",
+			matchers: "alertname=Watchdog",
+			timeout:  0,
+			want:     []api.DeadmanMatcher{{Name: "Watchdog", Labels: map[string]string{}}},
+			enabled:  false,
+		},
+		{
+			name:     "no usable matchers disables",
+			matchers: "",
+			timeout:  time.Hour,
+			want:     nil,
+			enabled:  false,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := api.ParseDeadmanConfig(tc.matchers, tc.timeout, "critical")
+			if len(got.Matchers) != len(tc.want) {
+				t.Fatalf("got %d matchers %v, want %d", len(got.Matchers), got.Matchers, len(tc.want))
+			}
+			for i, w := range tc.want {
+				if got.Matchers[i].Name != w.Name {
+					t.Errorf("matcher %d: name %q, want %q", i, got.Matchers[i].Name, w.Name)
+				}
+				if len(got.Matchers[i].Labels) != len(w.Labels) {
+					t.Errorf("matcher %d: labels %v, want %v", i, got.Matchers[i].Labels, w.Labels)
+					continue
+				}
+				for k, v := range w.Labels {
+					if got.Matchers[i].Labels[k] != v {
+						t.Errorf("matcher %d: label %s=%q, want %q", i, k, got.Matchers[i].Labels[k], v)
+					}
+				}
+			}
+		})
+	}
+}
+
+// A zero config is off, which is what keeps the feature opt-in for anything
+// building a router without one.
+func TestDeadman_DisabledConfigIsInert(t *testing.T) {
+	s, _ := deadmanTS(t, api.DeadmanConfig{})
+
+	heartbeat(t, s, "fp-watchdog", nil)
+	silence(t, s, "fp-watchdog", 48*time.Hour)
+	sweep(t, s, time.Hour)
+
+	// Ordinary alert handling: an incident from the arrival, not the absence.
+	if got := s.countIncidents(t); got != 1 {
+		t.Fatalf("expected plain alert handling with deadman off, got %d incidents", got)
+	}
+	if _, source, _ := s.alertRow(t, "fp-watchdog"); source == nil || *source != "expiry" {
+		t.Errorf("expected the generic sweeper to own the alert, got %v", source)
+	}
+}

internal/api/incident_store.go

@@ -8,7 +8,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/yeniklas/terdut-server/internal/models"
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 )
 
 // Values for incidents.resolution_source, recording who closed the incident:
@@ -16,6 +16,11 @@ import (
 const (
 	incidentResolutionAlerts = "alerts"
 	incidentResolutionManual = "manual"
+
+	// incidentResolutionRecovered closes a dead man's switch incident whose
+	// heartbeat started arriving again. It cannot be "alerts": these incidents
+	// have no member alerts for the cascade to work from.
+	incidentResolutionRecovered = "recovered"
 )
 
 // Incident timeline event types. Stored as free text so adding one later is not
@@ -31,6 +36,7 @@ const (
 	evUnsnoozed      = "unsnoozed"
 	evResolved       = "resolved"
 	evNote           = "note"
+	evDeadmanSilent  = "deadman_silent"
 )
 
 // severityLabel is the Alertmanager label an incident's severity is derived from.
@@ -223,7 +229,32 @@ func resolveIfSettled(ctx context.Context, q querier, incidentID int64) (bool, e
 	if n == 0 {
 		return false, nil
 	}
-	return true, logEvent(ctx, q, incidentID, evResolved, nil, nil, nil)
+	if err := logEvent(ctx, q, incidentID, evResolved, nil, nil, nil); err != nil {
+		return false, err
+	}
+	// The all-clear goes only to whoever was paged in the first place, which
+	// enqueueResolved works out from the incident's own notification history.
+	// Manual resolution sends nothing: the person who closed it already knows.
+	return true, enqueueResolved(ctx, q, incidentID)
+}
+
+// acknowledgeIncident records that userID has picked an incident up, and reports
+// whether it changed anything — an already-resolved incident is left alone.
+// Shared by the authenticated handler and the Acknowledge button in a push
+// notification, so both write the same state and the same timeline entry.
+func acknowledgeIncident(ctx context.Context, q querier, incidentID, userID int64) (bool, error) {
+	res, err := q.ExecContext(ctx, `
+		UPDATE incidents
+		   SET status = 'acknowledged', acknowledged_by = ?, acknowledged_at = ?
+		 WHERE id = ? AND resolved_at IS NULL`,
+		userID, time.Now().Unix(), incidentID)
+	if err != nil {
+		return false, err
+	}
+	if n, _ := res.RowsAffected(); n == 0 {
+		return false, nil
+	}
+	return true, logEvent(ctx, q, incidentID, evAcknowledged, &userID, nil, nil)
 }
 
 // openIncidentForAlert returns the open incident an alert currently belongs to,

internal/api/incidents.go

@@ -8,8 +8,8 @@ import (
 	"strings"
 	"time"
 
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 	"github.com/go-chi/chi/v5"
-	"github.com/yeniklas/terdut-server/internal/models"
 )
 
 func handleListIncidents(db *sql.DB) http.HandlerFunc {
@@ -189,13 +189,16 @@ func handleIncidentAcknowledge(db *sql.DB) http.HandlerFunc {
 			return
 		}
 		user, _ := userFromContext(r.Context())
-		if !updateOpenIncident(w, r, db, id,
-			`UPDATE incidents SET status = 'acknowledged', acknowledged_by = ?, acknowledged_at = ?
-			  WHERE id = ? AND resolved_at IS NULL`, user.ID, time.Now().Unix(), id) {
+		acked, err := acknowledgeIncident(r.Context(), db, id, user.ID)
+		if err != nil {
+			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
-		if err := logEvent(r.Context(), db, id, evAcknowledged, &user.ID, nil, nil); err != nil {
-			respond(w, http.StatusInternalServerError, errResp("internal error"))
+		if !acked {
+			if !incidentExists(w, r, db, id) {
+				return
+			}
+			respond(w, http.StatusConflict, errResp("incident is resolved"))
 			return
 		}
 		respondIncident(w, r, db, id)

internal/api/incidents_test.go

@@ -10,8 +10,8 @@ import (
 	"testing"
 	"time"
 
-	"github.com/yeniklas/terdut-server/internal/api"
-	"github.com/yeniklas/terdut-server/internal/db"
+	"git.ryuvia.com/niklas/terdut-server/internal/api"
+	"git.ryuvia.com/niklas/terdut-server/internal/db"
 )
 
 // amAlert builds one alert of a webhook payload.
@@ -613,7 +613,7 @@ func TestSweeper_ArchivesResolvedIncidents(t *testing.T) {
 
 	s.exec(t, "UPDATE incidents SET resolved_at = ? WHERE id = 1",
 		time.Now().Add(-30*24*time.Hour).Unix())
-	api.Sweep(context.Background(), s.db, 7*24*time.Hour, 6*time.Hour)
+	api.Sweep(context.Background(), s.db, 7*24*time.Hour, 6*time.Hour, s.deadman, s.notify)
 
 	if inc := getIncident(t, s, 1); inc["archived_at"] == nil {
 		t.Error("expected the sweeper to archive a long-resolved incident")
@@ -653,6 +653,61 @@ func TestStats_Incidents(t *testing.T) {
 	}
 }
 
+// An empty window is a report of zero, not a failure. SUM over no rows is NULL
+// in SQLite, which used to come back as a 500 the moment every incident was
+// archived — the state a quiet installation settles into.
+func TestStats_IncidentsEmptyWindowIsZeroNotAnError(t *testing.T) {
+	s := newTS(t)
+
+	// No incidents at all.
+	resp := s.req(t, http.MethodGet, "/api/stats/incidents", nil)
+	if resp.StatusCode != http.StatusOK {
+		resp.Body.Close()
+		t.Fatalf("expected 200 on an empty database, got %d", resp.StatusCode)
+	}
+	var stats map[string]any
+	decode(t, resp, &stats)
+	for _, k := range []string{"total", "triggered", "acknowledged", "resolved"} {
+		if stats[k].(float64) != 0 {
+			t.Errorf("expected %s 0, got %v", k, stats[k])
+		}
+	}
+
+	// And with every incident archived out of the window.
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-s4", "Gone", "firing", "2026-05-20T10:00:00Z", zeroTime, nil),
+	})
+	s.req(t, http.MethodPost, "/api/incidents/1/archive", nil).Body.Close()
+
+	resp = s.req(t, http.MethodGet, "/api/stats/incidents", nil)
+	if resp.StatusCode != http.StatusOK {
+		resp.Body.Close()
+		t.Fatalf("expected 200 when every incident is archived, got %d", resp.StatusCode)
+	}
+	stats = nil
+	decode(t, resp, &stats)
+	if stats["total"].(float64) != 0 {
+		t.Errorf("expected total 0, got %v", stats["total"])
+	}
+}
+
+// The alert stats share the same aggregate, and the same empty-window trap.
+func TestStats_AlertsEmptyWindowIsZeroNotAnError(t *testing.T) {
+	s := newTS(t)
+	resp := s.req(t, http.MethodGet, "/api/stats/alerts", nil)
+	if resp.StatusCode != http.StatusOK {
+		resp.Body.Close()
+		t.Fatalf("expected 200 on an empty database, got %d", resp.StatusCode)
+	}
+	var stats map[string]any
+	decode(t, resp, &stats)
+	for _, k := range []string{"total", "firing", "resolved"} {
+		if stats[k].(float64) != 0 {
+			t.Errorf("expected %s 0, got %v", k, stats[k])
+		}
+	}
+}
+
 // Nothing acknowledged yet means "no data", which is not the same claim as zero.
 func TestStats_IncidentsNullMTTAWhenNothingAcknowledged(t *testing.T) {
 	s := newTS(t)

internal/api/middleware.go

@@ -9,7 +9,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/yeniklas/terdut-server/internal/models"
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 )
 
 type contextKey string

internal/api/notifier.go

@@ -0,0 +1,563 @@
+package api
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+	"time"
+
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
+)
+
+const (
+	// notifyInterval is how often the notifier looks for work. The archiver's
+	// 15 minute tick is far too coarse for something that has to wake a person.
+	notifyInterval = 30 * time.Second
+
+	// notifyRetryBase and notifyRetryMax bound the delivery backoff. ntfy being
+	// briefly unreachable should not lose the page.
+	notifyRetryBase = 30 * time.Second
+	notifyRetryMax  = 15 * time.Minute
+
+	// notifyMaxAttempts stops a permanently undeliverable row from being retried
+	// forever. It keeps last_error so the reason survives.
+	notifyMaxAttempts = 8
+
+	// notifyBatch caps one delivery pass, so a large backlog cannot hold the
+	// single database connection for an unbounded stretch.
+	notifyBatch = 100
+
+	// ackTokenTTL is how long the Acknowledge button in a notification keeps
+	// working. Past this the notification is stale enough that the responder
+	// should look at the incident rather than blind-acknowledge it.
+	ackTokenTTL = 24 * time.Hour
+)
+
+// Notification kinds, recording why a push was sent.
+const (
+	notifyTriggered = "triggered"
+	notifyReminder  = "reminder"
+	notifyResolved  = "resolved"
+)
+
+// Timeline event types the notifier writes, so an incident's history says who
+// was paged and whether the page landed. Written from the delivery result
+// rather than at enqueue: a queued notification is an intention, and claiming
+// somebody was told before ntfy accepted it would be a lie the timeline keeps.
+//
+// The topic is deliberately absent from both. It is a shared secret with the
+// ntfy server — anyone holding it can publish to it — and the timeline is
+// readable by every API key.
+const (
+	eventNotified     = "notified"
+	eventNotifyFailed = "notify_failed"
+)
+
+// NotifyConfig is everything the notifier needs to reach ntfy and to build URLs
+// a phone can follow back to this server.
+type NotifyConfig struct {
+	// BaseURL is the ntfy server. Empty disables notifications entirely: no
+	// goroutine, and nothing is ever enqueued.
+	BaseURL string
+
+	// Token is an optional bearer token for an access-controlled ntfy.
+	Token string
+
+	// FallbackTopic receives incidents that open with nobody on call. Those
+	// notifications carry no Acknowledge button — there is no user to attribute
+	// the acknowledgement to, and putting one on a shared topic would let any
+	// subscriber acknowledge as somebody else.
+	FallbackTopic string
+
+	// PublicURL is the base URL a phone uses to reach this server, for the
+	// notification's click target and its Acknowledge action. Without it a
+	// notification is informational only.
+	PublicURL string
+
+	// RepeatEvery is how long an incident may sit unacknowledged before it is
+	// notified again. Zero disables reminders.
+	RepeatEvery time.Duration
+}
+
+// enabled reports whether notifications are configured at all.
+func (c NotifyConfig) enabled() bool { return c.BaseURL != "" }
+
+// notifyClient is shared: a page is small and infrequent, and the timeout is
+// what keeps a hung ntfy from stalling the delivery pass.
+var notifyClient = &http.Client{Timeout: 10 * time.Second}
+
+// StartNotifier delivers queued notifications until ctx is cancelled, starting
+// with an immediate pass so a restart flushes whatever the last one left behind.
+func StartNotifier(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
+	if !cfg.enabled() {
+		log.Print("notifier: disabled (no ntfy URL configured)")
+		return
+	}
+	log.Printf("notifier: publishing to %s", cfg.BaseURL)
+
+	ticker := time.NewTicker(notifyInterval)
+	defer ticker.Stop()
+
+	NotifySweep(ctx, db, cfg)
+	for {
+		select {
+		case <-ticker.C:
+			NotifySweep(ctx, db, cfg)
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
+// NotifySweep runs a single pass: queue reminders for incidents nobody has
+// picked up, then deliver everything that is due. Reminders are queued first so
+// a freshly due one goes out in the same pass rather than a tick later.
+// Exported so tests can drive a pass without waiting on the ticker.
+func NotifySweep(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
+	enqueueReminders(ctx, db, cfg)
+	deliverPending(ctx, db, cfg)
+}
+
+// enqueueReminders re-notifies incidents that are still sitting untouched.
+//
+// The stop conditions are the incident states that already mean "somebody has
+// this": acknowledged, snoozed, resolved, archived. Snooze in particular is the
+// mute button — a deliberate "not now" that should not keep buzzing — which is
+// why there is no separate reminder cap.
+//
+// The previous notification must have actually been sent before another is
+// queued, so an ntfy outage produces a retry backlog rather than a reminder
+// backlog that all lands at once when it comes back.
+func enqueueReminders(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
+	if cfg.RepeatEvery <= 0 {
+		return
+	}
+	now := time.Now()
+
+	type due struct {
+		incidentID int64
+		userID     *int64
+		topic      string
+	}
+
+	rows, err := db.QueryContext(ctx, `
+		SELECT n.incident_id, n.user_id, n.topic
+		FROM   notifications n
+		JOIN   incidents i ON i.id = n.incident_id
+		WHERE  n.id = (SELECT MAX(id) FROM notifications WHERE incident_id = n.incident_id)
+		  AND  n.sent_at IS NOT NULL
+		  AND  n.created_at <= ?
+		  AND  i.resolved_at IS NULL
+		  AND  i.archived_at IS NULL
+		  AND  i.status = 'triggered'
+		  AND  (i.snoozed_until IS NULL OR i.snoozed_until <= ?)`,
+		now.Add(-cfg.RepeatEvery).Unix(), now.Unix())
+	if err != nil {
+		log.Printf("notifier: find reminders: %v", err)
+		return
+	}
+
+	// Collected before inserting: the pool is limited to a single connection, so
+	// an open cursor would block the writes behind it.
+	var pending []due
+	for rows.Next() {
+		var d due
+		if err := rows.Scan(&d.incidentID, &d.userID, &d.topic); err != nil {
+			rows.Close()
+			log.Printf("notifier: scan reminder: %v", err)
+			return
+		}
+		pending = append(pending, d)
+	}
+	if err := rows.Err(); err != nil {
+		rows.Close()
+		log.Printf("notifier: find reminders: %v", err)
+		return
+	}
+	rows.Close()
+
+	for _, d := range pending {
+		if err := enqueueNotification(ctx, db, d.incidentID, d.userID, d.topic, notifyReminder); err != nil {
+			log.Printf("notifier: queue reminder for incident %d: %v", d.incidentID, err)
+		}
+	}
+	if len(pending) > 0 {
+		log.Printf("notifier: queued %d reminder(s)", len(pending))
+	}
+}
+
+// outboxRow is one queued notification, read before any HTTP happens.
+type outboxRow struct {
+	id         int64
+	incidentID int64
+	userID     *int64
+	topic      string
+	kind       string
+	attempts   int
+}
+
+// deliverPending sends everything that is due and records the outcome.
+func deliverPending(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
+	batch, err := pendingNotifications(ctx, db)
+	if err != nil {
+		log.Printf("notifier: find pending: %v", err)
+		return
+	}
+
+	sent := 0
+	for _, n := range batch {
+		if err := deliver(ctx, db, cfg, n); err != nil {
+			log.Printf("notifier: deliver %d (incident %d): %v", n.id, n.incidentID, err)
+			markFailed(ctx, db, n, err)
+			continue
+		}
+		if _, err := db.ExecContext(ctx,
+			"UPDATE notifications SET sent_at = ?, attempts = attempts + 1, last_error = NULL WHERE id = ?",
+			time.Now().Unix(), n.id); err != nil {
+			log.Printf("notifier: mark sent %d: %v", n.id, err)
+		}
+		// Logged, not returned: the page has already gone out, and treating a
+		// failed timeline write as a failed delivery would send it again.
+		if err := logEvent(ctx, db, n.incidentID, eventNotified, n.userID, nil, &n.kind); err != nil {
+			log.Printf("notifier: log delivery of %d: %v", n.id, err)
+		}
+		sent++
+	}
+	if sent > 0 {
+		log.Printf("notifier: delivered %d notification(s)", sent)
+	}
+}
+
+// pendingNotifications reads the due rows and closes the cursor before the
+// caller writes, for the same single-connection reason as staleAlertIDs.
+func pendingNotifications(ctx context.Context, db *sql.DB) ([]outboxRow, error) {
+	rows, err := db.QueryContext(ctx, `
+		SELECT id, incident_id, user_id, topic, kind, attempts
+		FROM   notifications
+		WHERE  sent_at IS NULL
+		  AND  send_after <= ?
+		  AND  attempts < ?
+		ORDER  BY id
+		LIMIT  ?`, time.Now().Unix(), notifyMaxAttempts, notifyBatch)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var batch []outboxRow
+	for rows.Next() {
+		var n outboxRow
+		if err := rows.Scan(&n.id, &n.incidentID, &n.userID, &n.topic, &n.kind, &n.attempts); err != nil {
+			return nil, err
+		}
+		batch = append(batch, n)
+	}
+	return batch, rows.Err()
+}
+
+// markFailed bumps the attempt count and pushes the row out to its next retry.
+//
+// The attempt that exhausts the budget also writes a timeline event. Without it
+// a page that never landed leaves the incident's history identical to one that
+// did, which is the failure most worth seeing: nobody was told, and nothing
+// says so.
+func markFailed(ctx context.Context, db *sql.DB, n outboxRow, cause error) {
+	next := time.Now().Add(retryDelay(n.attempts)).Unix()
+	if _, err := db.ExecContext(ctx,
+		"UPDATE notifications SET attempts = attempts + 1, send_after = ?, last_error = ? WHERE id = ?",
+		next, cause.Error(), n.id); err != nil {
+		log.Printf("notifier: mark failed %d: %v", n.id, err)
+	}
+
+	if n.attempts+1 < notifyMaxAttempts {
+		return
+	}
+	detail := fmt.Sprintf("%s: %s", n.kind, cause)
+	if err := logEvent(ctx, db, n.incidentID, eventNotifyFailed, n.userID, nil, &detail); err != nil {
+		log.Printf("notifier: log failure of %d: %v", n.id, err)
+	}
+}
+
+// retryDelay doubles the wait per attempt, up to notifyRetryMax.
+func retryDelay(attempts int) time.Duration {
+	d := notifyRetryBase << attempts
+	if d > notifyRetryMax || d <= 0 {
+		return notifyRetryMax
+	}
+	return d
+}
+
+// deliver renders one notification against the incident's *current* state and
+// publishes it. Rendering happens here rather than at enqueue time so a message
+// that waited in the queue while its incident escalated goes out at the
+// severity the incident has now.
+func deliver(ctx context.Context, db *sql.DB, cfg NotifyConfig, n outboxRow) error {
+	inc, err := fetchIncident(ctx, db, n.incidentID)
+	if err != nil {
+		return fmt.Errorf("load incident: %w", err)
+	}
+
+	var firing int
+	if err := db.QueryRowContext(ctx, `
+		SELECT COUNT(*)
+		FROM   incident_alerts ia
+		JOIN   alerts a ON a.id = ia.alert_id
+		WHERE  ia.incident_id = ? AND a.status = 'firing'`, n.incidentID).Scan(&firing); err != nil {
+		return fmt.Errorf("count firing: %w", err)
+	}
+
+	msg := renderNotification(inc, n, firing, cfg)
+
+	// An Acknowledge button needs both a user to attribute the acknowledgement
+	// to and a URL the phone can reach. Minted per delivery, so every push
+	// carries its own short-lived token rather than reusing one.
+	if n.kind != notifyResolved && n.userID != nil && cfg.PublicURL != "" {
+		raw, err := issueAckToken(ctx, db, n.incidentID, *n.userID)
+		if err != nil {
+			return fmt.Errorf("issue ack token: %w", err)
+		}
+		msg.Actions = append(msg.Actions, ntfyAction{
+			Action: "http",
+			Label:  "Acknowledge",
+			URL:    strings.TrimSuffix(cfg.PublicURL, "/") + "/api/notify/ack/" + raw,
+			Method: "POST",
+			Clear:  true,
+		})
+	}
+
+	return publish(ctx, cfg, msg)
+}
+
+// ntfyMessage is ntfy's JSON publish format. Using it rather than the X-Actions
+// header avoids that header's comma and quote escaping rules, which are easy to
+// break with a title that happens to contain a comma.
+type ntfyMessage struct {
+	Topic    string       `json:"topic"`
+	Title    string       `json:"title,omitempty"`
+	Message  string       `json:"message"`
+	Priority int          `json:"priority,omitempty"`
+	Tags     []string     `json:"tags,omitempty"`
+	Click    string       `json:"click,omitempty"`
+	Actions  []ntfyAction `json:"actions,omitempty"`
+}
+
+type ntfyAction struct {
+	Action string `json:"action"`
+	Label  string `json:"label"`
+	URL    string `json:"url"`
+	Method string `json:"method,omitempty"`
+	Clear  bool   `json:"clear,omitempty"`
+}
+
+// renderNotification builds the message body for one queued notification.
+func renderNotification(inc models.Incident, n outboxRow, firing int, cfg NotifyConfig) ntfyMessage {
+	msg := ntfyMessage{Topic: n.topic}
+
+	if cfg.PublicURL != "" {
+		msg.Click = fmt.Sprintf("%s/api/incidents/%d",
+			strings.TrimSuffix(cfg.PublicURL, "/"), inc.ID)
+	}
+
+	switch n.kind {
+	case notifyResolved:
+		msg.Title = "Resolved: " + inc.Title
+		msg.Message = "All alerts stopped firing after " +
+			humanDuration(time.Since(inc.TriggeredAt))
+		msg.Priority = ntfyPriorityLow
+		msg.Tags = []string{"white_check_mark"}
+		return msg
+
+	case notifyReminder:
+		msg.Title = "Still unacknowledged: " + inc.Title
+	default:
+		msg.Title = inc.Title
+	}
+
+	severity := derefString(inc.Severity)
+
+	parts := []string{fmt.Sprintf("%d alert%s firing", firing, plural(firing))}
+	if severity != "" {
+		parts = append(parts, "severity "+severity)
+	}
+	if assignee := derefString(inc.AssignedToUser); assignee != "" {
+		parts = append(parts, "on call: "+assignee)
+	}
+	if n.kind == notifyReminder {
+		parts = append(parts, "open "+humanDuration(time.Since(inc.TriggeredAt)))
+	}
+
+	msg.Message = strings.Join(parts, " · ")
+	msg.Priority = ntfyPriority(severity)
+	msg.Tags = []string{severityTag(severity)}
+	return msg
+}
+
+// ntfy's priority scale. Max is the one that overrides the phone's quiet
+// settings, which is the whole point of paging on critical.
+const (
+	ntfyPriorityLow     = 2
+	ntfyPriorityDefault = 3
+	ntfyPriorityHigh    = 4
+	ntfyPriorityMax     = 5
+)
+
+// ntfyPriority maps an incident's severity onto ntfy's scale, following the
+// same ordering severityRank uses. An unrecognised severity gets the default
+// rather than being silenced.
+func ntfyPriority(severity string) int {
+	switch severityRank(severity) {
+	case 4:
+		return ntfyPriorityMax
+	case 3:
+		return ntfyPriorityHigh
+	case 2:
+		return ntfyPriorityDefault
+	case 1:
+		return ntfyPriorityLow
+	default:
+		return ntfyPriorityDefault
+	}
+}
+
+func severityTag(severity string) string {
+	switch severityRank(severity) {
+	case 4:
+		return "rotating_light"
+	case 3:
+		return "red_circle"
+	case 2:
+		return "warning"
+	case 1:
+		return "information_source"
+	default:
+		return "bell"
+	}
+}
+
+// publish POSTs one message to ntfy.
+func publish(ctx context.Context, cfg NotifyConfig, msg ntfyMessage) error {
+	body, err := json.Marshal(msg)
+	if err != nil {
+		return err
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+		strings.TrimSuffix(cfg.BaseURL, "/"), bytes.NewReader(body))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	if cfg.Token != "" {
+		req.Header.Set("Authorization", "Bearer "+cfg.Token)
+	}
+
+	resp, err := notifyClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("ntfy returned %s", resp.Status)
+	}
+	return nil
+}
+
+// enqueueNotification adds one row to the outbox, due immediately.
+func enqueueNotification(ctx context.Context, q querier, incidentID int64, userID *int64, topic, kind string) error {
+	now := time.Now().Unix()
+	_, err := q.ExecContext(ctx, `
+		INSERT INTO notifications (incident_id, user_id, topic, kind, created_at, send_after)
+		VALUES (?, ?, ?, ?, ?, ?)`, incidentID, userID, topic, kind, now, now)
+	return err
+}
+
+// notifyTarget decides where a newly opened incident's notification goes.
+//
+// The on-call user's own topic when they have one, otherwise the fallback
+// topic with no user attached. Deliberately not "the fallback topic, attributed
+// to the on-call user": the fallback is shared, and an Acknowledge button on a
+// shared topic would let any subscriber acknowledge as somebody else.
+func notifyTarget(ctx context.Context, q querier, cfg NotifyConfig, onCall *int64) (topic string, userID *int64) {
+	if onCall != nil {
+		var t *string
+		err := q.QueryRowContext(ctx,
+			"SELECT ntfy_topic FROM users WHERE id = ?", *onCall).Scan(&t)
+		if err == nil && t != nil && *t != "" {
+			return *t, onCall
+		}
+	}
+	return cfg.FallbackTopic, nil
+}
+
+// enqueueOpened queues the notification for a freshly opened incident. It is the
+// only enqueue point that has to resolve a topic from scratch; every later
+// notification for the incident reuses what this one chose.
+func enqueueOpened(ctx context.Context, q querier, cfg NotifyConfig, incidentID int64, onCall *int64) error {
+	if !cfg.enabled() {
+		return nil
+	}
+	topic, userID := notifyTarget(ctx, q, cfg, onCall)
+	if topic == "" {
+		// Nobody on call has a topic and there is no fallback: there is nowhere
+		// to send this, and queueing it would only accumulate undeliverable rows.
+		return nil
+	}
+	return enqueueNotification(ctx, q, incidentID, userID, topic, notifyTriggered)
+}
+
+// enqueueResolved queues the all-clear, reusing the topic the incident's last
+// notification went to. That needs no configuration to reach this function, and
+// it gives the right rule for free: you only hear that something resolved if you
+// were told it started.
+func enqueueResolved(ctx context.Context, q querier, incidentID int64) error {
+	var topic string
+	var userID *int64
+	err := q.QueryRowContext(ctx, `
+		SELECT topic, user_id FROM notifications
+		 WHERE incident_id = ? ORDER BY id DESC LIMIT 1`, incidentID).Scan(&topic, &userID)
+	if err == sql.ErrNoRows {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	return enqueueNotification(ctx, q, incidentID, userID, topic, notifyResolved)
+}
+
+// humanDuration renders an age the way a person reads it at 3am: coarse, and
+// never more than two units.
+func humanDuration(d time.Duration) string {
+	if d < time.Minute {
+		return "less than a minute"
+	}
+	if d < time.Hour {
+		return fmt.Sprintf("%dm", int(d.Minutes()))
+	}
+	h := int(d.Hours())
+	m := int(d.Minutes()) - h*60
+	if m == 0 {
+		return fmt.Sprintf("%dh", h)
+	}
+	return fmt.Sprintf("%dh%dm", h, m)
+}
+
+func plural(n int) string {
+	if n == 1 {
+		return ""
+	}
+	return "s"
+}
+
+// derefString reads a nullable text column as a plain string.
+func derefString(s *string) string {
+	if s == nil {
+		return ""
+	}
+	return *s
+}

internal/api/notify_ack.go

@@ -0,0 +1,98 @@
+package api
+
+import (
+	"context"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/hex"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// issueAckToken mints the secret behind one notification's Acknowledge button
+// and returns the raw value to embed in its URL. Only the hash is stored, the
+// same way api_keys works.
+//
+// A fresh token per delivery rather than one per incident: the raw value only
+// exists for as long as it takes to build the message, so there is nothing to
+// look up and reuse later, and a reminder that supersedes an earlier page
+// carries its own credential.
+func issueAckToken(ctx context.Context, q querier, incidentID, userID int64) (string, error) {
+	raw, hash, err := randomToken()
+	if err != nil {
+		return "", err
+	}
+	now := time.Now()
+	if _, err := q.ExecContext(ctx, `
+		INSERT INTO incident_ack_tokens (token_hash, incident_id, user_id, created_at, expires_at)
+		VALUES (?, ?, ?, ?, ?)`,
+		hash, incidentID, userID, now.Unix(), now.Add(ackTokenTTL).Unix()); err != nil {
+		return "", err
+	}
+	return raw, nil
+}
+
+// handleNotifyAck acknowledges an incident from the Acknowledge button in a
+// push notification.
+//
+// It is deliberately outside AuthMiddleware: the caller is a phone acting on a
+// notification, not a client holding an API key. What stands in for the key is
+// the token in the path — 256 bits of entropy, valid for one incident, one
+// action, and one day. It must stay publicly reachable for the button to work
+// when the responder is off the cluster network.
+func handleNotifyAck(db *sql.DB) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		h := sha256.Sum256([]byte(chi.URLParam(r, "token")))
+		hash := hex.EncodeToString(h[:])
+
+		var incidentID, userID int64
+		err := db.QueryRowContext(r.Context(), `
+			SELECT incident_id, user_id FROM incident_ack_tokens
+			 WHERE token_hash = ? AND expires_at > ?`,
+			hash, time.Now().Unix()).Scan(&incidentID, &userID)
+		if err != nil {
+			// Unknown and expired get the same answer, so the endpoint cannot be
+			// used to probe which tokens once existed.
+			respond(w, http.StatusNotFound, errResp("invalid or expired token"))
+			return
+		}
+
+		acked, err := acknowledgeIncident(r.Context(), db, incidentID, userID)
+		if err != nil {
+			respond(w, http.StatusInternalServerError, errResp("internal error"))
+			return
+		}
+		if !acked {
+			// The incident closed between the page and the tap. Nothing to do,
+			// and nothing the responder did wrong — report the state, not an error,
+			// so ntfy shows a success toast rather than a failure.
+			respond(w, http.StatusOK, map[string]any{
+				"incident_id": incidentID,
+				"status":      "resolved",
+			})
+			return
+		}
+		respond(w, http.StatusOK, map[string]any{
+			"incident_id": incidentID,
+			"status":      "acknowledged",
+		})
+	}
+}
+
+// purgeAckTokens drops tokens whose notifications are long past. Nothing else
+// deletes them: incidents are archived rather than removed, so the cascade never
+// fires in practice.
+func purgeAckTokens(ctx context.Context, db *sql.DB) {
+	res, err := db.ExecContext(ctx,
+		"DELETE FROM incident_ack_tokens WHERE expires_at < ?", time.Now().Unix())
+	if err != nil {
+		log.Printf("sweeper: purge ack tokens: %v", err)
+		return
+	}
+	if n, _ := res.RowsAffected(); n > 0 {
+		log.Printf("sweeper: purged %d expired ack token(s)", n)
+	}
+}

internal/api/notify_test.go

@@ -0,0 +1,724 @@
+package api_test
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.ryuvia.com/niklas/terdut-server/internal/api"
+)
+
+// ---------------------------------------------------------------------------
+// Fake ntfy
+// ---------------------------------------------------------------------------
+
+// pushed is one message the fake ntfy received, in ntfy's JSON publish shape.
+type pushed struct {
+	Topic    string   `json:"topic"`
+	Title    string   `json:"title"`
+	Message  string   `json:"message"`
+	Priority int      `json:"priority"`
+	Tags     []string `json:"tags"`
+	Click    string   `json:"click"`
+	Actions  []struct {
+		Action string `json:"action"`
+		Label  string `json:"label"`
+		URL    string `json:"url"`
+		Method string `json:"method"`
+		Clear  bool   `json:"clear"`
+	} `json:"actions"`
+}
+
+// fakeNtfy records what the notifier published. status controls the reply, so a
+// test can make delivery fail.
+type fakeNtfy struct {
+	*httptest.Server
+	mu     sync.Mutex
+	got    []pushed
+	status int
+}
+
+func newFakeNtfy(t *testing.T) *fakeNtfy {
+	t.Helper()
+	f := &fakeNtfy{status: http.StatusOK}
+	f.Server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var msg pushed
+		if err := json.NewDecoder(r.Body).Decode(&msg); err != nil {
+			http.Error(w, "bad json", http.StatusBadRequest)
+			return
+		}
+		f.mu.Lock()
+		f.got = append(f.got, msg)
+		status := f.status
+		f.mu.Unlock()
+		w.WriteHeader(status)
+	}))
+	t.Cleanup(f.Close)
+	return f
+}
+
+func (f *fakeNtfy) messages() []pushed {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return append([]pushed(nil), f.got...)
+}
+
+func (f *fakeNtfy) failWith(status int) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.status = status
+}
+
+// ---------------------------------------------------------------------------
+// Harness
+// ---------------------------------------------------------------------------
+
+// notifyTS builds a server with notifications enabled, the admin on call today,
+// and a topic on the admin — the setup every delivery test needs.
+func notifyTS(t *testing.T, cfg api.NotifyConfig) (*ts, *fakeNtfy) {
+	t.Helper()
+	f := newFakeNtfy(t)
+	cfg.BaseURL = f.URL
+	s := newTS(t, cfg)
+
+	putOnCall(t, s, 1)
+	setTopic(t, s, 1, "terdut-admin")
+	return s, f
+}
+
+func putOnCall(t *testing.T, s *ts, userID int) {
+	t.Helper()
+	today := time.Now().UTC().Format("2006-01-02")
+	resp := s.req(t, http.MethodPost, "/api/schedule",
+		map[string]any{"user_id": userID, "dates": []string{today}})
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("schedule assignment returned %d", resp.StatusCode)
+	}
+}
+
+func setTopic(t *testing.T, s *ts, userID int, topic string) {
+	t.Helper()
+	resp := s.req(t, http.MethodPut,
+		fmt.Sprintf("/api/users/%d/notify", userID), map[string]any{"ntfy_topic": topic})
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("set notify topic returned %d", resp.StatusCode)
+	}
+}
+
+func (s *ts) sweepNotify(t *testing.T) {
+	t.Helper()
+	api.NotifySweep(context.Background(), s.db, s.notify)
+}
+
+// countNotifications reports how many outbox rows exist, optionally of one kind.
+func (s *ts) countNotifications(t *testing.T, kind string) int {
+	t.Helper()
+	var n int
+	query := "SELECT COUNT(*) FROM notifications"
+	args := []any{}
+	if kind != "" {
+		query += " WHERE kind = ?"
+		args = append(args, kind)
+	}
+	if err := s.db.QueryRow(query, args...).Scan(&n); err != nil {
+		t.Fatalf("count notifications: %v", err)
+	}
+	return n
+}
+
+// fireCritical posts a single critical alert, which opens one incident.
+func fireCritical(t *testing.T, s *ts) {
+	t.Helper()
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-notify", "DiskFull", "firing", "2026-05-20T10:00:00Z", zeroTime,
+			map[string]string{"severity": "critical"}),
+	}, "{}:{alertname=\"DiskFull\"}")
+}
+
+// ---------------------------------------------------------------------------
+// Delivery
+// ---------------------------------------------------------------------------
+
+func TestNotify_TriggeredIncidentPagesOnCall(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+
+	if got := s.countNotifications(t, "triggered"); got != 1 {
+		t.Fatalf("expected 1 queued notification, got %d", got)
+	}
+	s.sweepNotify(t)
+
+	msgs := f.messages()
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 push, got %d", len(msgs))
+	}
+	m := msgs[0]
+
+	if m.Topic != "terdut-admin" {
+		t.Errorf("expected the on-call user's topic, got %q", m.Topic)
+	}
+	if m.Priority != 5 {
+		t.Errorf("expected max priority for a critical incident, got %d", m.Priority)
+	}
+	if !strings.Contains(m.Title, "DiskFull") {
+		t.Errorf("expected the incident title in %q", m.Title)
+	}
+	if !strings.Contains(m.Message, "severity critical") {
+		t.Errorf("expected the severity in %q", m.Message)
+	}
+	if m.Click != "https://terdut.example.com/api/incidents/1" {
+		t.Errorf("unexpected click target %q", m.Click)
+	}
+	if len(m.Actions) != 1 || m.Actions[0].Label != "Acknowledge" {
+		t.Fatalf("expected an Acknowledge action, got %+v", m.Actions)
+	}
+	if m.Actions[0].Method != http.MethodPost {
+		t.Errorf("expected the action to POST, got %q", m.Actions[0].Method)
+	}
+}
+
+// A delivered row must not be delivered again on the next pass.
+func TestNotify_DeliveredOnlyOnce(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.sweepNotify(t)
+
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected 1 push across two passes, got %d", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Delivery on the timeline
+// ---------------------------------------------------------------------------
+
+// notifyEvents picks the notifier's entries out of an incident's timeline.
+// Asserted through the API rather than the table: the timeline is what the
+// clients read, so its shape is the contract worth covering.
+func notifyEvents(t *testing.T, s *ts, id int) []map[string]any {
+	t.Helper()
+	var out []map[string]any
+	for _, e := range timeline(t, s, id) {
+		if e["type"] == "notified" || e["type"] == "notify_failed" {
+			out = append(out, e)
+		}
+	}
+	return out
+}
+
+func TestNotify_DeliveryIsRecordedOnTheTimeline(t *testing.T) {
+	s, _ := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	// Queued is not notified: nothing is on the timeline until ntfy accepts it.
+	if got := notifyEvents(t, s, 1); len(got) != 0 {
+		t.Fatalf("expected no event before delivery, got %v", got)
+	}
+
+	s.sweepNotify(t)
+
+	events := notifyEvents(t, s, 1)
+	if len(events) != 1 {
+		t.Fatalf("expected 1 notification event, got %v", events)
+	}
+	e := events[0]
+	if e["type"] != "notified" {
+		t.Errorf("expected a notified event, got %v", e["type"])
+	}
+	if e["detail"] != "triggered" {
+		t.Errorf("expected the kind in detail, got %v", e["detail"])
+	}
+	if e["username"] != "admin" {
+		t.Errorf("expected the paged user attached, got %v", e["username"])
+	}
+	// The topic is a shared secret with ntfy; the timeline is not the place for it.
+	for _, v := range e {
+		if s, ok := v.(string); ok && strings.Contains(s, "terdut-admin") {
+			t.Errorf("expected the topic kept out of the timeline, found it in %v", e)
+		}
+	}
+}
+
+// A redelivery-free pass must not double-log either.
+func TestNotify_TimelineRecordsOneEventPerDelivery(t *testing.T) {
+	s, _ := notifyTS(t, api.NotifyConfig{
+		PublicURL:   "https://terdut.example.com",
+		RepeatEvery: 15 * time.Minute,
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.sweepNotify(t)
+	s.ageNotifications(t, 20*time.Minute)
+	s.sweepNotify(t)
+
+	events := notifyEvents(t, s, 1)
+	if len(events) != 2 {
+		t.Fatalf("expected one event per delivery, got %v", events)
+	}
+	if events[0]["detail"] != "triggered" || events[1]["detail"] != "reminder" {
+		t.Errorf("expected triggered then reminder, got %v and %v",
+			events[0]["detail"], events[1]["detail"])
+	}
+}
+
+func TestNotify_AllClearIsRecordedOnTheTimeline(t *testing.T) {
+	s, _ := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-notify", "DiskFull", "resolved", "2026-05-20T10:00:00Z",
+			"2026-05-20T11:00:00Z", map[string]string{"severity": "critical"}),
+	}, "{}:{alertname=\"DiskFull\"}")
+	s.sweepNotify(t)
+
+	events := notifyEvents(t, s, 1)
+	if len(events) != 2 {
+		t.Fatalf("expected the all-clear recorded, got %v", events)
+	}
+	if events[1]["detail"] != "resolved" {
+		t.Errorf("expected a resolved event, got %v", events[1]["detail"])
+	}
+}
+
+// A page to the shared fallback belongs to nobody, and the timeline has to say
+// so rather than attributing it to whoever happens to be on call now.
+func TestNotify_FallbackDeliveryHasNoUser(t *testing.T) {
+	f := newFakeNtfy(t)
+	s := newTS(t, api.NotifyConfig{
+		BaseURL:       f.URL,
+		FallbackTopic: "terdut-oncall",
+		PublicURL:     "https://terdut.example.com",
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	events := notifyEvents(t, s, 1)
+	if len(events) != 1 {
+		t.Fatalf("expected 1 notification event, got %v", events)
+	}
+	if got, ok := events[0]["username"]; ok && got != nil && got != "" {
+		t.Errorf("expected no user on a fallback-topic page, got %v", got)
+	}
+}
+
+// The failure worth seeing: nobody was paged, and the timeline says so instead
+// of looking exactly like a delivery that worked.
+func TestNotify_ExhaustedRetriesAreRecordedOnce(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+	f.failWith(http.StatusInternalServerError)
+
+	fireCritical(t, s)
+	// One pass per attempt, each made due by clearing the backoff the last one set.
+	for i := 0; i < 10; i++ {
+		s.sweepNotify(t)
+		s.exec(t, "UPDATE notifications SET send_after = ? WHERE sent_at IS NULL",
+			time.Now().Add(-time.Second).Unix())
+	}
+
+	events := notifyEvents(t, s, 1)
+	if len(events) != 1 {
+		t.Fatalf("expected exactly one failure event, got %v", events)
+	}
+	if events[0]["type"] != "notify_failed" {
+		t.Errorf("expected notify_failed, got %v", events[0]["type"])
+	}
+	detail, _ := events[0]["detail"].(string)
+	if !strings.HasPrefix(detail, "triggered: ") || !strings.Contains(detail, "500") {
+		t.Errorf("expected the kind and the reason in %q", detail)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Acknowledging from the notification
+// ---------------------------------------------------------------------------
+
+func TestNotify_AckButtonAcknowledgesIncident(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	ackURL := f.messages()[0].Actions[0].URL
+	// The action URL is built for the public hostname; point it at the test
+	// server, which is the same handler.
+	path := ackURL[strings.Index(ackURL, "/api/notify/ack/"):]
+
+	resp, err := http.Post(s.URL+path, "application/json", nil)
+	if err != nil {
+		t.Fatalf("ack: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("expected 200 from the ack button, got %d", resp.StatusCode)
+	}
+
+	inc := getIncident(t, s, 1)
+	if inc["status"] != "acknowledged" {
+		t.Errorf("expected the incident acknowledged, got %v", inc["status"])
+	}
+	if inc["acknowledged_by"] != "admin" {
+		t.Errorf("expected the ack attributed to the token's user, got %v", inc["acknowledged_by"])
+	}
+
+	// The timeline must record it the same way the authenticated route would.
+	events := timeline(t, s, 1)
+	if !contains(eventTypes(events), "acknowledged") {
+		t.Errorf("expected an acknowledged event, got %v", eventTypes(events))
+	}
+	for _, e := range events {
+		if e["type"] == "acknowledged" && e["username"] != "admin" {
+			t.Errorf("expected the acknowledged event attributed to admin, got %v", e["username"])
+		}
+	}
+}
+
+func TestNotify_AckRejectsUnknownToken(t *testing.T) {
+	s, _ := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+	fireCritical(t, s)
+
+	resp, err := http.Post(s.URL+"/api/notify/ack/deadbeef", "application/json", nil)
+	if err != nil {
+		t.Fatalf("ack: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusNotFound {
+		t.Errorf("expected 404 for an unknown token, got %d", resp.StatusCode)
+	}
+	if inc := getIncident(t, s, 1); inc["status"] != "triggered" {
+		t.Errorf("expected the incident untouched, got %v", inc["status"])
+	}
+}
+
+func TestNotify_AckRejectsExpiredToken(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	ackURL := f.messages()[0].Actions[0].URL
+	path := ackURL[strings.Index(ackURL, "/api/notify/ack/"):]
+
+	// Age the token past its TTL. The token's inputs are wall-clock timestamps,
+	// so this is the same trick the sweeper tests use.
+	s.exec(t, "UPDATE incident_ack_tokens SET expires_at = ?", time.Now().Add(-time.Minute).Unix())
+
+	resp, err := http.Post(s.URL+path, "application/json", nil)
+	if err != nil {
+		t.Fatalf("ack: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusNotFound {
+		t.Errorf("expected 404 for an expired token, got %d", resp.StatusCode)
+	}
+	if inc := getIncident(t, s, 1); inc["status"] != "triggered" {
+		t.Errorf("expected the incident untouched, got %v", inc["status"])
+	}
+}
+
+// The sweeper is what stops expired tokens accumulating forever.
+func TestNotify_SweepPurgesExpiredAckTokens(t *testing.T) {
+	s, _ := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.exec(t, "UPDATE incident_ack_tokens SET expires_at = ?", time.Now().Add(-time.Minute).Unix())
+
+	api.Sweep(context.Background(), s.db, 168*time.Hour, 6*time.Hour, s.deadman, s.notify)
+
+	var n int
+	if err := s.db.QueryRow("SELECT COUNT(*) FROM incident_ack_tokens").Scan(&n); err != nil {
+		t.Fatalf("count tokens: %v", err)
+	}
+	if n != 0 {
+		t.Errorf("expected expired tokens purged, %d left", n)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Reminders
+// ---------------------------------------------------------------------------
+
+// ageNotifications backdates every sent notification so the next pass sees the
+// reminder as due.
+func (s *ts) ageNotifications(t *testing.T, by time.Duration) {
+	t.Helper()
+	s.exec(t, "UPDATE notifications SET created_at = ? WHERE sent_at IS NOT NULL",
+		time.Now().Add(-by).Unix())
+}
+
+func TestNotify_UnacknowledgedIncidentIsRenotified(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{
+		PublicURL:   "https://terdut.example.com",
+		RepeatEvery: 15 * time.Minute,
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.ageNotifications(t, 20*time.Minute)
+	s.sweepNotify(t)
+
+	msgs := f.messages()
+	if len(msgs) != 2 {
+		t.Fatalf("expected a reminder push, got %d message(s)", len(msgs))
+	}
+	if !strings.Contains(msgs[1].Title, "Still unacknowledged") {
+		t.Errorf("expected the reminder to say so, got %q", msgs[1].Title)
+	}
+	if msgs[1].Topic != "terdut-admin" {
+		t.Errorf("expected the reminder on the same topic, got %q", msgs[1].Topic)
+	}
+	// Each page carries its own credential.
+	if len(msgs[1].Actions) != 1 || msgs[1].Actions[0].URL == msgs[0].Actions[0].URL {
+		t.Errorf("expected the reminder to carry a fresh ack token")
+	}
+}
+
+func TestNotify_AcknowledgedIncidentStopsReminders(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{
+		PublicURL:   "https://terdut.example.com",
+		RepeatEvery: 15 * time.Minute,
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	resp := s.req(t, http.MethodPost, "/api/incidents/1/acknowledge", nil)
+	resp.Body.Close()
+
+	s.ageNotifications(t, 20*time.Minute)
+	s.sweepNotify(t)
+
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected no reminder once acknowledged, got %d message(s)", got)
+	}
+}
+
+// Snooze is the deliberate "not now", and it is what mutes the pager.
+func TestNotify_SnoozedIncidentStopsReminders(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{
+		PublicURL:   "https://terdut.example.com",
+		RepeatEvery: 15 * time.Minute,
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	resp := s.req(t, http.MethodPost, "/api/incidents/1/snooze", map[string]any{"duration": "1h"})
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("snooze returned %d", resp.StatusCode)
+	}
+	resp.Body.Close()
+
+	s.ageNotifications(t, 20*time.Minute)
+	s.sweepNotify(t)
+
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected no reminder while snoozed, got %d message(s)", got)
+	}
+}
+
+func TestNotify_ZeroRepeatDisablesReminders(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.ageNotifications(t, 24*time.Hour)
+	s.sweepNotify(t)
+
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected reminders off, got %d message(s)", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Resolution
+// ---------------------------------------------------------------------------
+
+func TestNotify_ResolvedIncidentSendsAllClear(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-notify", "DiskFull", "resolved", "2026-05-20T10:00:00Z",
+			"2026-05-20T11:00:00Z", map[string]string{"severity": "critical"}),
+	}, "{}:{alertname=\"DiskFull\"}")
+	s.sweepNotify(t)
+
+	msgs := f.messages()
+	if len(msgs) != 2 {
+		t.Fatalf("expected an all-clear push, got %d message(s)", len(msgs))
+	}
+	if !strings.HasPrefix(msgs[1].Title, "Resolved:") {
+		t.Errorf("expected a resolved title, got %q", msgs[1].Title)
+	}
+	if msgs[1].Priority != 2 {
+		t.Errorf("expected the all-clear at low priority, got %d", msgs[1].Priority)
+	}
+	// Nothing to acknowledge on a closed incident.
+	if len(msgs[1].Actions) != 0 {
+		t.Errorf("expected no actions on the all-clear, got %+v", msgs[1].Actions)
+	}
+}
+
+// Closing an incident by hand sends nothing: the person who did it knows.
+func TestNotify_ManualResolveSendsNothing(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	resp := s.req(t, http.MethodPost, "/api/incidents/1/resolve", nil)
+	resp.Body.Close()
+	s.sweepNotify(t)
+
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected no push for a manual resolve, got %d message(s)", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Routing and configuration
+// ---------------------------------------------------------------------------
+
+// With nobody on call the page goes to the shared fallback, and carries no
+// Acknowledge button — there is no user to attribute the acknowledgement to.
+func TestNotify_FallbackTopicHasNoAckButton(t *testing.T) {
+	f := newFakeNtfy(t)
+	s := newTS(t, api.NotifyConfig{
+		BaseURL:       f.URL,
+		FallbackTopic: "terdut-oncall",
+		PublicURL:     "https://terdut.example.com",
+	})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	msgs := f.messages()
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 push, got %d", len(msgs))
+	}
+	if msgs[0].Topic != "terdut-oncall" {
+		t.Errorf("expected the fallback topic, got %q", msgs[0].Topic)
+	}
+	if len(msgs[0].Actions) != 0 {
+		t.Errorf("expected no ack button on a shared topic, got %+v", msgs[0].Actions)
+	}
+}
+
+// Nobody on call and no fallback means there is nowhere to send: queueing would
+// only pile up rows that can never be delivered.
+func TestNotify_NoTargetQueuesNothing(t *testing.T) {
+	f := newFakeNtfy(t)
+	s := newTS(t, api.NotifyConfig{BaseURL: f.URL})
+
+	fireCritical(t, s)
+
+	if got := s.countNotifications(t, ""); got != 0 {
+		t.Errorf("expected nothing queued without a target, got %d", got)
+	}
+	s.sweepNotify(t)
+	if got := len(f.messages()); got != 0 {
+		t.Errorf("expected no push, got %d", got)
+	}
+}
+
+// The zero NotifyConfig is what every pre-existing test runs under.
+func TestNotify_DisabledQueuesNothing(t *testing.T) {
+	s := newTS(t)
+	putOnCall(t, s, 1)
+	setTopic(t, s, 1, "terdut-admin")
+
+	fireCritical(t, s)
+
+	if got := s.countNotifications(t, ""); got != 0 {
+		t.Errorf("expected nothing queued with notifications off, got %d", got)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Retries
+// ---------------------------------------------------------------------------
+
+func TestNotify_FailedDeliveryRetriesWithBackoff(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+	f.failWith(http.StatusInternalServerError)
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	var attempts int
+	var sentAt *int64
+	var sendAfter int64
+	var lastError *string
+	if err := s.db.QueryRow(
+		"SELECT attempts, sent_at, send_after, last_error FROM notifications WHERE id = 1").
+		Scan(&attempts, &sentAt, &sendAfter, &lastError); err != nil {
+		t.Fatalf("read notification: %v", err)
+	}
+	if attempts != 1 {
+		t.Errorf("expected 1 attempt recorded, got %d", attempts)
+	}
+	if sentAt != nil {
+		t.Errorf("expected the row unsent, got sent_at %v", *sentAt)
+	}
+	if sendAfter <= time.Now().Unix() {
+		t.Errorf("expected the retry pushed into the future, got %d", sendAfter)
+	}
+	if lastError == nil || !strings.Contains(*lastError, "500") {
+		t.Errorf("expected the failure recorded, got %v", lastError)
+	}
+
+	// Backing off means the next pass leaves it alone until it is due.
+	s.sweepNotify(t)
+	if got := len(f.messages()); got != 1 {
+		t.Errorf("expected no immediate retry, got %d attempt(s)", got)
+	}
+
+	// Once due and once ntfy recovers, it goes out.
+	f.failWith(http.StatusOK)
+	s.exec(t, "UPDATE notifications SET send_after = ? WHERE id = 1", time.Now().Add(-time.Second).Unix())
+	s.sweepNotify(t)
+
+	if err := s.db.QueryRow("SELECT sent_at FROM notifications WHERE id = 1").Scan(&sentAt); err != nil {
+		t.Fatalf("read notification: %v", err)
+	}
+	if sentAt == nil {
+		t.Error("expected the retry to succeed once ntfy recovered")
+	}
+}
+
+// An ntfy outage must not produce a reminder backlog that all lands at once
+// when it comes back: the previous page has to have been sent first.
+func TestNotify_UnsentNotificationBlocksReminders(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{
+		PublicURL:   "https://terdut.example.com",
+		RepeatEvery: 15 * time.Minute,
+	})
+	f.failWith(http.StatusInternalServerError)
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+	s.exec(t, "UPDATE notifications SET created_at = ?", time.Now().Add(-time.Hour).Unix())
+	s.sweepNotify(t)
+
+	if got := s.countNotifications(t, "reminder"); got != 0 {
+		t.Errorf("expected no reminders queued behind an undelivered page, got %d", got)
+	}
+}

internal/api/router.go

@@ -8,7 +8,11 @@ import (
 	"github.com/go-chi/chi/v5/middleware"
 )
 
-func NewRouter(db *sql.DB) http.Handler {
+// NewRouter builds the HTTP surface. notify and deadman are passed through to
+// the webhook, the only handler that has to decide where a new incident's page
+// goes and which arriving alerts are heartbeats rather than problems. A zero
+// notify disables notifications; a zero deadman disables dead man's switches.
+func NewRouter(db *sql.DB, notify NotifyConfig, deadman DeadmanConfig) http.Handler {
 	r := chi.NewRouter()
 	r.Use(middleware.Logger)
 	r.Use(middleware.Recoverer)
@@ -17,9 +21,13 @@ func NewRouter(db *sql.DB) http.Handler {
 		respond(w, http.StatusOK, map[string]string{"status": "ok"})
 	})
 
-	// Unauthenticated: bootstrap and Alertmanager webhook receiver.
+	// Unauthenticated: bootstrap, the Alertmanager webhook receiver, and the
+	// Acknowledge button in a push notification. The last one is authorised by
+	// the scoped token in its path rather than an API key, and has to stay
+	// reachable from outside the cluster for the button to work.
 	r.Post("/api/bootstrap", handleBootstrap(db))
-	r.Post("/api/alertmanager/webhook", handleAlertmanagerWebhook(db))
+	r.Post("/api/alertmanager/webhook", handleAlertmanagerWebhook(db, notify, deadman))
+	r.Post("/api/notify/ack/{token}", handleNotifyAck(db))
 
 	// All other /api routes require a valid API key.
 	r.Group(func(r chi.Router) {
@@ -28,6 +36,7 @@ func NewRouter(db *sql.DB) http.Handler {
 		r.Get("/api/users", handleListUsers(db))
 		r.Post("/api/users", handleCreateUser(db))
 		r.Delete("/api/users/{id}", handleDeleteUser(db))
+		r.Put("/api/users/{id}/notify", handleSetNotifyTarget(db))
 		r.Post("/api/users/{id}/api-keys", handleCreateAPIKey(db))
 		r.Delete("/api/users/{id}/api-keys/{keyID}", handleDeleteAPIKey(db))
 

internal/api/schedule.go

@@ -8,8 +8,8 @@ import (
 	"strings"
 	"time"
 
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 	"github.com/go-chi/chi/v5"
-	"github.com/yeniklas/terdut-server/internal/models"
 )
 
 func handleCreateSchedule(db *sql.DB) http.HandlerFunc {
@@ -17,6 +17,12 @@ func handleCreateSchedule(db *sql.DB) http.HandlerFunc {
 		var req struct {
 			UserID int64    `json:"user_id"`
 			Dates  []string `json:"dates"`
+
+			// Replace takes dates that somebody else already holds. It defaults
+			// to off so that the plain call cannot quietly move a shift off the
+			// person expecting to be paged for it — reassigning has to be asked
+			// for.
+			Replace bool `json:"replace"`
 		}
 		if err := decodeJSON(r, &req); err != nil {
 			respond(w, http.StatusBadRequest, errResp("invalid request body"))
@@ -44,7 +50,10 @@ func handleCreateSchedule(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		// All-or-nothing: if any date already has an assignment, reject the whole request.
+		// All-or-nothing, in both directions: without replace, one taken date
+		// rejects the whole request; with it, either every date moves or none
+		// does. The rota must never be left with a hole where a shift used to
+		// be, so the delete and the insert share one transaction.
 		tx, err := db.BeginTx(r.Context(), nil)
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
@@ -53,10 +62,18 @@ func handleCreateSchedule(db *sql.DB) http.HandlerFunc {
 		defer tx.Rollback()
 
 		for _, d := range req.Dates {
+			if req.Replace {
+				if _, err := tx.ExecContext(r.Context(),
+					"DELETE FROM schedule_entries WHERE date = ?", d); err != nil {
+					respond(w, http.StatusInternalServerError, errResp("internal error"))
+					return
+				}
+			}
 			if _, err := tx.ExecContext(r.Context(),
 				"INSERT INTO schedule_entries (user_id, date) VALUES (?, ?)", req.UserID, d); err != nil {
 				if strings.Contains(err.Error(), "UNIQUE constraint failed") {
-					respond(w, http.StatusConflict, errResp("date already assigned: "+d))
+					respond(w, http.StatusConflict,
+						errResp("date already assigned: "+d+" (pass replace to take it)"))
 					return
 				}
 				respond(w, http.StatusInternalServerError, errResp("internal error"))

internal/api/stats.go

@@ -13,11 +13,14 @@ func handleStatsAlerts(db *sql.DB) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		where, args := statsFilter(r.URL.Query(), "received_at")
 
+		// COALESCE because SUM over zero rows is NULL, not 0, and a count of
+		// nothing is 0 — without it an empty window is a 500 rather than a
+		// legitimately empty report.
 		var total, firing, resolved int64
 		err := db.QueryRowContext(r.Context(), fmt.Sprintf(`
 			SELECT COUNT(*),
-			       SUM(CASE WHEN status = 'firing'   THEN 1 ELSE 0 END),
-			       SUM(CASE WHEN status = 'resolved' THEN 1 ELSE 0 END)
+			       COALESCE(SUM(CASE WHEN status = 'firing'   THEN 1 ELSE 0 END), 0),
+			       COALESCE(SUM(CASE WHEN status = 'resolved' THEN 1 ELSE 0 END), 0)
 			FROM alerts WHERE %s`, where), args...,
 		).Scan(&total, &firing, &resolved)
 		if err != nil {
@@ -167,13 +170,16 @@ func handleStatsIncidents(db *sql.DB) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		where, args := statsFilter(r.URL.Query(), "triggered_at")
 
+		// The counts are COALESCEd because SUM over zero rows is NULL, not 0.
+		// The averages are not: mtta and mttr stay null on purpose, since zero
+		// would read as "instant" rather than "nothing to measure yet".
 		var total, triggered, acknowledged, resolved int64
 		var mtta, mttr *float64
 		err := db.QueryRowContext(r.Context(), fmt.Sprintf(`
 			SELECT COUNT(*),
-			       SUM(CASE WHEN status = 'triggered'    THEN 1 ELSE 0 END),
-			       SUM(CASE WHEN status = 'acknowledged' THEN 1 ELSE 0 END),
-			       SUM(CASE WHEN status = 'resolved'     THEN 1 ELSE 0 END),
+			       COALESCE(SUM(CASE WHEN status = 'triggered'    THEN 1 ELSE 0 END), 0),
+			       COALESCE(SUM(CASE WHEN status = 'acknowledged' THEN 1 ELSE 0 END), 0),
+			       COALESCE(SUM(CASE WHEN status = 'resolved'     THEN 1 ELSE 0 END), 0),
 			       AVG(CASE WHEN acknowledged_at IS NOT NULL
 			                THEN acknowledged_at - triggered_at END),
 			       AVG(CASE WHEN resolved_at IS NOT NULL

internal/api/users.go

@@ -11,8 +11,8 @@ import (
 	"strings"
 	"time"
 
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 	"github.com/go-chi/chi/v5"
-	"github.com/yeniklas/terdut-server/internal/models"
 )
 
 func handleBootstrap(db *sql.DB) http.HandlerFunc {
@@ -48,7 +48,7 @@ func handleBootstrap(db *sql.DB) http.HandlerFunc {
 		}
 		userID, _ := res.LastInsertId()
 
-		raw, hash, err := newAPIKey()
+		raw, hash, err := randomToken()
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
@@ -70,7 +70,7 @@ func handleBootstrap(db *sql.DB) http.HandlerFunc {
 func handleListUsers(db *sql.DB) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		rows, err := db.QueryContext(r.Context(),
-			"SELECT id, username, email, created_at FROM users ORDER BY id")
+			"SELECT id, username, email, created_at, ntfy_topic FROM users ORDER BY id")
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
@@ -81,7 +81,7 @@ func handleListUsers(db *sql.DB) http.HandlerFunc {
 		for rows.Next() {
 			var u models.User
 			var ts int64
-			if err := rows.Scan(&u.ID, &u.Username, &u.Email, &ts); err != nil {
+			if err := rows.Scan(&u.ID, &u.Username, &u.Email, &ts, &u.NtfyTopic); err != nil {
 				respond(w, http.StatusInternalServerError, errResp("internal error"))
 				return
 			}
@@ -123,6 +123,50 @@ func handleCreateUser(db *sql.DB) http.HandlerFunc {
 	}
 }
 
+// handleSetNotifyTarget points a user's push notifications at an ntfy topic, or
+// clears it with an empty string. The topic is a shared secret with the ntfy
+// server — anyone who knows it can publish to it — so pick an unguessable one
+// unless your ntfy enforces access control.
+func handleSetNotifyTarget(db *sql.DB) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
+		if err != nil {
+			respond(w, http.StatusBadRequest, errResp("invalid user id"))
+			return
+		}
+		var req struct {
+			NtfyTopic string `json:"ntfy_topic"`
+		}
+		if err := decodeJSON(r, &req); err != nil {
+			respond(w, http.StatusBadRequest, errResp("invalid request body"))
+			return
+		}
+
+		var topic *string
+		if t := strings.TrimSpace(req.NtfyTopic); t != "" {
+			topic = &t
+		}
+
+		res, err := db.ExecContext(r.Context(),
+			"UPDATE users SET ntfy_topic = ? WHERE id = ?", topic, id)
+		if err != nil {
+			respond(w, http.StatusInternalServerError, errResp("internal error"))
+			return
+		}
+		if n, _ := res.RowsAffected(); n == 0 {
+			respond(w, http.StatusNotFound, errResp("user not found"))
+			return
+		}
+
+		user, err := fetchUser(r.Context(), db, id)
+		if err != nil {
+			respond(w, http.StatusInternalServerError, errResp("internal error"))
+			return
+		}
+		respond(w, http.StatusOK, user)
+	}
+}
+
 func handleDeleteUser(db *sql.DB) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
@@ -170,7 +214,7 @@ func handleCreateAPIKey(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		raw, hash, err := newAPIKey()
+		raw, hash, err := randomToken()
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
@@ -215,8 +259,9 @@ func handleDeleteAPIKey(db *sql.DB) http.HandlerFunc {
 	}
 }
 
-// newAPIKey generates a random 32-byte key encoded as hex, plus its SHA-256 hash for storage.
-func newAPIKey() (raw, hash string, err error) {
+// randomToken generates a random 32-byte secret encoded as hex, plus its SHA-256
+// hash for storage. Used for API keys and for notification acknowledge tokens.
+func randomToken() (raw, hash string, err error) {
 	b := make([]byte, 32)
 	if _, err = rand.Read(b); err != nil {
 		return
@@ -230,8 +275,9 @@ func newAPIKey() (raw, hash string, err error) {
 func fetchUser(ctx context.Context, db *sql.DB, id int64) (models.User, error) {
 	var u models.User
 	var ts int64
-	err := db.QueryRowContext(ctx, "SELECT id, username, email, created_at FROM users WHERE id = ?", id).
-		Scan(&u.ID, &u.Username, &u.Email, &ts)
+	err := db.QueryRowContext(ctx,
+		"SELECT id, username, email, created_at, ntfy_topic FROM users WHERE id = ?", id).
+		Scan(&u.ID, &u.Username, &u.Email, &ts, &u.NtfyTopic)
 	if err != nil {
 		return u, err
 	}

internal/config/config.go

@@ -14,6 +14,44 @@ type Config struct {
 	// before the sweeper treats it as resolved. It must exceed Alertmanager's
 	// repeat_interval (default 4h), which is what refreshes the alert.
 	StaleAfter time.Duration
+
+	// DeadmanMatchers selects the alerts that are heartbeats rather than
+	// problems: receiving one opens no incident, and the absence of one does.
+	//
+	// ";" separates matchers, "," the label conditions within one, "=" is exact
+	// equality — `alertname=Watchdog,cluster=prod; alertname=Heartbeat`. Every
+	// matcher must name an alertname. See api.ParseDeadmanConfig.
+	DeadmanMatchers string
+
+	// DeadmanTimeout is how long a heartbeat may go unheard before its switch is
+	// declared dead. It must be *shorter* than the Alertmanager repeat_interval
+	// of the route carrying the heartbeat — the opposite of StaleAfter, and the
+	// reason a dead man's switch usually wants a route of its own. Zero disables
+	// dead man's switch handling entirely.
+	DeadmanTimeout time.Duration
+
+	// DeadmanSeverity is the severity a dead man's switch incident opens at.
+	// These incidents have no member alerts to derive one from.
+	DeadmanSeverity string
+
+	// NtfyURL is the ntfy server push notifications are published to. Empty
+	// disables notifications entirely.
+	NtfyURL string
+
+	// NtfyToken is an optional bearer token for an access-controlled ntfy.
+	NtfyToken string
+
+	// NtfyFallbackTopic receives incidents that open with nobody on call.
+	NtfyFallbackTopic string
+
+	// PublicURL is the base URL a phone uses to reach this server, used for the
+	// link and the Acknowledge button inside a notification. Without it
+	// notifications carry neither.
+	PublicURL string
+
+	// NotifyRepeat is how long an incident may sit unacknowledged before it is
+	// notified again. Zero disables reminders.
+	NotifyRepeat time.Duration
 }
 
 func Load() Config {
@@ -25,17 +63,40 @@ func Load() Config {
 	if dbPath == "" {
 		dbPath = "terdut.db"
 	}
-	archiveAfter := 7 * 24 * time.Hour
-	if s := os.Getenv("TERDUT_ARCHIVE_AFTER"); s != "" {
-		if d, err := time.ParseDuration(s); err == nil {
-			archiveAfter = d
-		}
+	deadmanMatchers := os.Getenv("TERDUT_DEADMAN_MATCHERS")
+	if deadmanMatchers == "" {
+		deadmanMatchers = "alertname=Watchdog"
 	}
-	staleAfter := 6 * time.Hour
-	if s := os.Getenv("TERDUT_STALE_AFTER"); s != "" {
-		if d, err := time.ParseDuration(s); err == nil {
-			staleAfter = d
-		}
+	deadmanSeverity := os.Getenv("TERDUT_DEADMAN_SEVERITY")
+	if deadmanSeverity == "" {
+		deadmanSeverity = "critical"
+	}
+	return Config{
+		Addr:         addr,
+		DBPath:       dbPath,
+		ArchiveAfter: duration("TERDUT_ARCHIVE_AFTER", 7*24*time.Hour),
+		StaleAfter:   duration("TERDUT_STALE_AFTER", 6*time.Hour),
+
+		DeadmanMatchers: deadmanMatchers,
+		DeadmanTimeout:  duration("TERDUT_DEADMAN_TIMEOUT", 15*time.Minute),
+		DeadmanSeverity: deadmanSeverity,
+
+		NtfyURL:           os.Getenv("TERDUT_NTFY_URL"),
+		NtfyToken:         os.Getenv("TERDUT_NTFY_TOKEN"),
+		NtfyFallbackTopic: os.Getenv("TERDUT_NTFY_FALLBACK_TOPIC"),
+		PublicURL:         os.Getenv("TERDUT_PUBLIC_URL"),
+		NotifyRepeat:      duration("TERDUT_NOTIFY_REPEAT", 15*time.Minute),
 	}
-	return Config{Addr: addr, DBPath: dbPath, ArchiveAfter: archiveAfter, StaleAfter: staleAfter}
+}
+
+// duration reads a time.ParseDuration-formatted env var. An unset or
+// unparseable value falls back to def rather than failing startup: a typo in one
+// tuning knob should not take the server down.
+func duration(env string, def time.Duration) time.Duration {
+	if s := os.Getenv(env); s != "" {
+		if d, err := time.ParseDuration(s); err == nil {
+			return d
+		}
+	}
+	return def
 }

internal/db/migrations/009_notifications.sql

@@ -0,0 +1,44 @@
+-- Adds push notification delivery, so an incident reaches the person on call
+-- instead of waiting to be discovered.
+--
+-- Delivery is an outbox rather than an inline HTTP call: the pool is limited to
+-- a single connection, so a POST made while holding the webhook's transaction
+-- would stall every other request behind it. The webhook inserts a row; the
+-- notifier goroutine delivers it.
+
+CREATE TABLE notifications (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    incident_id INTEGER NOT NULL REFERENCES incidents(id) ON DELETE CASCADE,
+    -- Nullable: a notification sent to the fallback topic belongs to nobody,
+    -- because nobody was on call when the incident opened.
+    user_id     INTEGER REFERENCES users(id) ON DELETE SET NULL,
+    topic       TEXT    NOT NULL,              -- resolved at enqueue: who was on call then
+    kind        TEXT    NOT NULL CHECK(kind IN ('triggered', 'reminder', 'resolved')),
+    created_at  INTEGER NOT NULL,
+    send_after  INTEGER NOT NULL,              -- retry backoff watermark
+    attempts    INTEGER NOT NULL DEFAULT 0,
+    sent_at     INTEGER,
+    last_error  TEXT                           -- kept after the last attempt, for debugging
+);
+
+-- The delivery loop's only query: what is due and still unsent.
+CREATE INDEX notifications_pending_idx  ON notifications(send_after) WHERE sent_at IS NULL;
+-- Reminders and resolved notices both look up an incident's newest row.
+CREATE INDEX notifications_incident_idx ON notifications(incident_id, id DESC);
+
+-- A notification body is stored on the ntfy server and cached on the device, so
+-- a real API key must never appear in one. Each delivery mints its own token
+-- instead: one incident, one action, one day.
+CREATE TABLE incident_ack_tokens (
+    token_hash  TEXT    PRIMARY KEY,           -- SHA-256 of the raw token, as with api_keys
+    incident_id INTEGER NOT NULL REFERENCES incidents(id) ON DELETE CASCADE,
+    user_id     INTEGER NOT NULL REFERENCES users(id)     ON DELETE CASCADE,
+    created_at  INTEGER NOT NULL,
+    expires_at  INTEGER NOT NULL
+);
+
+CREATE INDEX incident_ack_tokens_expires_idx ON incident_ack_tokens(expires_at);
+
+-- Where this user's notifications go. NULL means they get none; incidents
+-- assigned to them fall back to the configured fallback topic.
+ALTER TABLE users ADD COLUMN ntfy_topic TEXT;

internal/models/user.go

@@ -7,6 +7,11 @@ type User struct {
 	Username  string    `json:"username"`
 	Email     string    `json:"email"`
 	CreatedAt time.Time `json:"created_at"`
+
+	// NtfyTopic is where this user's push notifications go. Nil means they get
+	// none of their own; incidents assigned to them fall back to the configured
+	// fallback topic instead.
+	NtfyTopic *string `json:"ntfy_topic,omitempty"`
 }
 
 type APIKey struct {