Set the chart's placeholder version to 0.37.2

Every incident-mutation handler read userFromContext(ctx) and wrote the
result's .ID into acknowledged_by/incident_events.user_id without checking
the ok bool. For a team-scoped service-account caller this returned a
zero-value user id, which violated the users(id) FK and 500'd on
acknowledge, unacknowledge, resolve, snooze, unsnooze and create-note.
handleDeleteNote didn't crash but silently matched zero rows instead
(WHERE user_id = 0), so a service account could never delete its own note.

Add acknowledged_by_service_account_id (incidents) and service_account_id
(incident_events) as nullable FKs to service_accounts(id), parallel to and
mutually exclusive with the existing human columns (migration 015, with a
CHECK enforcing the exclusion). Route every one of the six handlers plus
delete-note through a new callerActorIDs() helper that branches on
Caller.AsHuman()/ServiceAccountID() instead of assuming a human, and thread
a serviceAccountID parameter through logEvent and the new
acknowledgeIncidentAs (acknowledgeIncident itself is untouched: its only
other caller, the push-notification Acknowledge button, is always human).
Render the new actor distinctly from both a human and "the server acted"
in the web UI's incident timeline and facts card.

handleIncidentAssign, handleIncidentArchive and handleIncidentUnarchive are
deliberately not touched here — they track no actor at all today, for
anyone, which is a separate pre-existing gap (follow-up issue to come).

Fixes #25

charts/terdut-server/Chart.yaml

@@ -15,5 +15,5 @@ type: application
 # 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: 0.35.0
-appVersion: "v0.35.0"
+version: 0.37.2
+appVersion: "v0.37.2"

charts/terdut-server/templates/deployment.yaml

@@ -6,15 +6,19 @@ metadata:
   labels:
     {{- include "terdut-server.labels" . | nindent 4 }}
 spec:
-  replicas: 1
+  replicas: {{ .Values.replicaCount }}
   selector:
     matchLabels:
       {{- include "terdut-server.selectorLabels" . | nindent 6 }}
-  # Recreate, not RollingUpdate, even though the PVC that forced it is gone: the
-  # sweeper and the notifier are unsynchronised singletons, and two replicas
-  # overlapping during a rollout would both page for the same incident.
+  # RollingUpdate, not Recreate: the sweeper, notifier and migration runner
+  # each take a Postgres advisory lock around their own pass, and new-incident
+  # creation on the first webhook for a brand-new groupKey resolves its own
+  # insert conflict -- so two replicas overlapping during a rollout no longer
+  # double-page, race a migration, or drop a webhook payload (v0.36.0). No
+  # explicit maxUnavailable/maxSurge: the 25%/25% default rounds to 0/1 at
+  # replicaCount: 2, which is zero-downtime already.
   strategy:
-    type: Recreate
+    type: RollingUpdate
   template:
     metadata:
       labels:

charts/terdut-server/values.yaml

@@ -1,3 +1,10 @@
+# Safe above 1 since v0.36.0: the sweeper, notifier and migration runner each
+# take a Postgres advisory lock around their own pass, and a webhook that
+# loses the race to open a brand-new incident attaches to the winner's row
+# instead of dropping its payload. An image older than v0.36.0 does not have
+# these guards -- do not raise this against one.
+replicaCount: 2
+
 networking:
   hostname: "terdut.example.com"
   servicePort: 8080

internal/api/advisory_lock_test.go

@@ -0,0 +1,122 @@
+package api
+
+// This file is internal (package api, not api_test) because withAdvisoryLock is
+// unexported and these tests exercise its locking semantics directly rather than
+// through the full StartArchiver/StartNotifier loop, which would make the "does
+// not run while held" case timing-dependent instead of deterministic. It opens a
+// plain connection to TERDUT_TEST_DSN rather than reusing testdb_test.go's
+// newTestDB, since that helper lives in the separate, already-compiled
+// api_test package and a Postgres advisory lock needs no schema or migration
+// to exercise.
+
+import (
+	"context"
+	"database/sql"
+	"os"
+	"testing"
+
+	_ "github.com/jackc/pgx/v5/stdlib"
+)
+
+// advisoryTestDB opens a plain, unmigrated connection to the test database. An
+// unset DSN fails rather than skips, matching testdb_test.go's rationale: a
+// suite that quietly tests nothing is worse than one that does not run.
+func advisoryTestDB(t *testing.T) *sql.DB {
+	t.Helper()
+
+	dsn := os.Getenv("TERDUT_TEST_DSN")
+	if dsn == "" {
+		t.Fatalf("TERDUT_TEST_DSN is not set: these tests need Postgres.\n" +
+			"Run `make test-db` for a local one, then\n" +
+			"  export TERDUT_TEST_DSN=postgres://terdut:terdut@localhost:5432/terdut_test?sslmode=disable")
+	}
+
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatalf("connect to TERDUT_TEST_DSN: %v", err)
+	}
+	t.Cleanup(func() { db.Close() })
+	return db
+}
+
+func TestWithAdvisoryLock_RunsWhenFree(t *testing.T) {
+	db := advisoryTestDB(t)
+	ctx := context.Background()
+
+	ran := false
+	withAdvisoryLock(ctx, db, archiverLockKey, "test", func() { ran = true })
+
+	if !ran {
+		t.Fatal("fn did not run although the lock was free")
+	}
+}
+
+func TestWithAdvisoryLock_SkipsWhileHeldElsewhere(t *testing.T) {
+	db := advisoryTestDB(t)
+	ctx := context.Background()
+
+	// Hold the lock on a connection of our own, standing in for another
+	// replica mid-pass.
+	holder, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("acquire holder connection: %v", err)
+	}
+	defer holder.Close()
+	if _, err := holder.ExecContext(ctx, "SELECT pg_advisory_lock($1)", archiverLockKey); err != nil {
+		t.Fatalf("pre-acquire lock: %v", err)
+	}
+
+	ran := false
+	withAdvisoryLock(ctx, db, archiverLockKey, "test", func() { ran = true })
+	if ran {
+		t.Fatal("fn ran although another connection already held the lock")
+	}
+
+	if _, err := holder.ExecContext(ctx, "SELECT pg_advisory_unlock($1)", archiverLockKey); err != nil {
+		t.Fatalf("release held lock: %v", err)
+	}
+
+	// Now that the holder released it, the next caller should get it.
+	ran = false
+	withAdvisoryLock(ctx, db, archiverLockKey, "test", func() { ran = true })
+	if !ran {
+		t.Fatal("fn did not run after the other connection released the lock")
+	}
+}
+
+func TestWithAdvisoryLock_ReleasesAfterFnReturns(t *testing.T) {
+	db := advisoryTestDB(t)
+	ctx := context.Background()
+
+	withAdvisoryLock(ctx, db, notifierLockKey, "test", func() {})
+
+	// If the first call had leaked the lock, this one would see it held and
+	// skip, leaving ran false.
+	ran := false
+	withAdvisoryLock(ctx, db, notifierLockKey, "test", func() { ran = true })
+	if !ran {
+		t.Fatal("fn did not run on a later call: the earlier call leaked its lock")
+	}
+}
+
+func TestWithAdvisoryLock_KeysAreIndependent(t *testing.T) {
+	db := advisoryTestDB(t)
+	ctx := context.Background()
+
+	holder, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("acquire holder connection: %v", err)
+	}
+	defer holder.Close()
+	if _, err := holder.ExecContext(ctx, "SELECT pg_advisory_lock($1)", archiverLockKey); err != nil {
+		t.Fatalf("pre-acquire archiver lock: %v", err)
+	}
+	defer holder.ExecContext(ctx, "SELECT pg_advisory_unlock($1)", archiverLockKey)
+
+	// Holding archiverLockKey must not block notifierLockKey.
+	ran := false
+	withAdvisoryLock(ctx, db, notifierLockKey, "test", func() { ran = true })
+	if !ran {
+		t.Fatal("fn did not run under a different key although only archiverLockKey was held")
+	}
+}

internal/api/alertmanager.go

@@ -169,7 +169,7 @@ func ingest(ctx context.Context, db *sql.DB, notify NotifyConfig, src alertSourc
 		}
 		touched[id] = true
 		alertID := a.id
-		if err := logEvent(ctx, tx, id, evAlertResolved, nil, &alertID, nil); err != nil {
+		if err := logEvent(ctx, tx, id, evAlertResolved, nil, nil, &alertID, nil); err != nil {
 			return err
 		}
 	}
@@ -376,6 +376,17 @@ func incidentForGroup(ctx context.Context, tx *sql.Tx, notify NotifyConfig, team
 // 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.
+//
+// Both callers get here only after their own SELECT found no open incident for
+// this group_key — but on more than one replica, two webhook deliveries for the
+// very first occurrence of a brand-new group_key can both pass that SELECT
+// before either INSERTs. ON CONFLICT DO NOTHING against
+// incidents_open_group_key_idx is what makes the loser's INSERT a no-op instead
+// of a unique-violation error that would otherwise roll back its entire
+// payload; existingOpenIncident then hands it the winner's row. Postgres
+// resolves that conflict only once the winner's transaction has committed (or
+// rolled back), so by the time this RETURNING comes back empty, the winner's
+// row is guaranteed visible to that follow-up SELECT.
 func openIncident(ctx context.Context, q querier, notify NotifyConfig, teamID int64, groupKey, title string, groupLabels map[string]string, severity *string) (int64, error) {
 	onCall, err := currentOnCall(ctx, q, teamID)
 	if err != nil {
@@ -391,19 +402,27 @@ func openIncident(ctx context.Context, q querier, notify NotifyConfig, teamID in
 	err = q.QueryRowContext(ctx, `
 		INSERT INTO incidents (team_id, group_key, title, group_labels, signature, status, severity, triggered_at, assigned_to)
 		VALUES ($1, $2, $3, $4::jsonb, $5, 'triggered', $6, $7, $8)
+		ON CONFLICT (team_id, group_key) WHERE resolved_at IS NULL DO NOTHING
 		RETURNING id`,
 		teamID, groupKey, title, string(labelsJSON), incidentSignature(groupLabels, title), severity,
 		time.Now().Unix(), onCall).Scan(&id)
-	if err != nil {
+	switch {
+	case err == sql.ErrNoRows:
+		// Lost the race: someone else's incident for this group_key exists now.
+		// Everything below — the trigger event, assignment, page, escalation
+		// clock — already happened for that row when it was created; attach to
+		// it rather than fail this call (and the whole payload) outright.
+		return existingOpenIncident(ctx, q, teamID, groupKey)
+	case err != nil:
 		return 0, err
 	}
 
-	if err := logEvent(ctx, q, id, evTriggered, nil, nil, nil); err != nil {
+	if err := logEvent(ctx, q, id, evTriggered, nil, 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, q, id, evAssigned, onCall, nil, nil); err != nil {
+		if err := logEvent(ctx, q, id, evAssigned, onCall, nil, nil, nil); err != nil {
 			return 0, err
 		}
 	}
@@ -423,6 +442,21 @@ func openIncident(ctx context.Context, q querier, notify NotifyConfig, teamID in
 	return id, nil
 }
 
+// existingOpenIncident looks up the open incident openIncident's own INSERT just
+// lost a conflict against — the same lookup incidentForGroup does before ever
+// calling openIncident, repeated here for the caller that arrived second.
+func existingOpenIncident(ctx context.Context, q querier, teamID int64, groupKey string) (int64, error) {
+	var id int64
+	err := q.QueryRowContext(ctx,
+		"SELECT id FROM incidents WHERE team_id = $1 AND group_key = $2 AND resolved_at IS NULL",
+		teamID, groupKey,
+	).Scan(&id)
+	if err != nil {
+		return 0, err
+	}
+	return id, nil
+}
+
 // linkAlert adds an alert to an incident, emitting a timeline entry only the
 // first time. Re-sends of an already-linked alert are silent.
 func linkAlert(ctx context.Context, tx *sql.Tx, incidentID, alertID int64) error {
@@ -436,5 +470,5 @@ func linkAlert(ctx context.Context, tx *sql.Tx, incidentID, alertID int64) error
 	if n, _ := res.RowsAffected(); n == 0 {
 		return nil
 	}
-	return logEvent(ctx, tx, incidentID, evAlertAdded, nil, &alertID, nil)
+	return logEvent(ctx, tx, incidentID, evAlertAdded, nil, nil, &alertID, nil)
 }

internal/api/alertmanager_test.go

@@ -0,0 +1,112 @@
+package api_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"sync"
+	"testing"
+)
+
+// TestWebhook_ConcurrentFirstOccurrenceOpensOneIncident reproduces two
+// replicas racing the very first webhook delivery for a brand-new group_key:
+// both see no open incident yet (incidentForGroup's own SELECT finds
+// nothing) and race openIncident's INSERT.
+//
+// The DB's own unique index already guarantees at most one incident either
+// way, with or without this fix — so "exactly one incident" alone cannot
+// tell a fixed run from a broken one. What ON CONFLICT handling actually
+// changes is what happens to the *loser*: before it, the loser's INSERT hit
+// incidents_open_group_key_idx's unique violation, which — since
+// upsertAlerts ran earlier in that same transaction — rolled back its whole
+// payload, alert insert included. ingest's error is only logged and
+// receiveWebhook answers 200 regardless, so nothing ever retried it: the
+// loser's alert silently never existed. That is the regression signal this
+// test checks — every caller's fingerprint must show up in /api/alerts, not
+// just the winner's.
+func TestWebhook_ConcurrentFirstOccurrenceOpensOneIncident(t *testing.T) {
+	s := newTS(t)
+
+	const callers = 8
+	const groupKey = "race-group"
+
+	// Every caller needs its own fingerprint. A shared one would serialize all
+	// of them at upsertAlerts' own ON CONFLICT (team_id, fingerprint) row lock,
+	// long before any of them reached incidentForGroup — which would hide the
+	// very race this test exists to force.
+	bodies := make([][]byte, callers)
+	for i := range callers {
+		payload := map[string]any{
+			"version":     "4",
+			"status":      "firing",
+			"groupKey":    groupKey,
+			"groupLabels": map[string]string{"alertname": "RaceAlert"},
+			"alerts": []map[string]any{amAlert(fmt.Sprintf("fp-race-%d", i), "RaceAlert", "firing",
+				"2026-05-20T10:00:00Z", "0001-01-01T00:00:00Z", nil)},
+		}
+		bodies[i], _ = json.Marshal(payload)
+	}
+
+	// A start line, so every request is fired as close to simultaneously as
+	// goroutine scheduling allows, rather than trickling out one dial at a
+	// time — the race window is the gap between incidentForGroup's SELECT and
+	// openIncident's INSERT, which a staggered start could easily miss.
+	var ready sync.WaitGroup
+	start := make(chan struct{})
+	statuses := make([]int, callers)
+	var wg sync.WaitGroup
+	for i := range callers {
+		ready.Add(1)
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			ready.Done()
+			<-start
+			resp, err := http.Post(s.URL+"/api/integrations/"+s.ingestKey+"/alertmanager",
+				"application/json", bytes.NewReader(bodies[i]))
+			if err != nil {
+				t.Errorf("post webhook #%d: %v", i, err)
+				return
+			}
+			defer resp.Body.Close()
+			statuses[i] = resp.StatusCode
+		}(i)
+	}
+	ready.Wait()
+	close(start)
+	wg.Wait()
+
+	for i, code := range statuses {
+		if code != http.StatusOK {
+			t.Errorf("webhook #%d returned %d, want 200", i, code)
+		}
+	}
+
+	var matched []any
+	for _, inc := range listIncidents(t, s, "") {
+		if inc["group_key"] == groupKey {
+			matched = append(matched, inc["id"])
+		}
+	}
+	if len(matched) != 1 {
+		t.Fatalf("expected exactly 1 incident for group_key %q after %d concurrent deliveries, got %d: %v",
+			groupKey, callers, len(matched), matched)
+	}
+
+	var alerts []map[string]any
+	decode(t, s.req(t, http.MethodGet, "/api/alerts", nil), &alerts)
+	seen := map[string]bool{}
+	for _, a := range alerts {
+		if fp, ok := a["fingerprint"].(string); ok {
+			seen[fp] = true
+		}
+	}
+	for i := range callers {
+		fp := fmt.Sprintf("fp-race-%d", i)
+		if !seen[fp] {
+			t.Errorf("alert %q is missing: its delivery's whole payload was silently rolled back "+
+				"when it lost the race for the incident", fp)
+		}
+	}
+}

internal/api/archiver.go

@@ -15,6 +15,12 @@ const (
 	// expiryGrace absorbs clock skew and notification latency before an alert
 	// whose ends_at watermark has passed is treated as stale.
 	expiryGrace = 5 * time.Minute
+
+	// archiverLockKey is the Postgres advisory lock the sweeper takes for the
+	// duration of each pass, so that running more than one replica does not run
+	// the sweep concurrently on all of them. Its value has no meaning beyond
+	// being distinct from notifierLockKey.
+	archiverLockKey int64 = 7265_0001
 )
 
 // StartArchiver runs the alert sweeper until ctx is cancelled, starting with an
@@ -23,15 +29,25 @@ const (
 // the fallback, not the setting: each pass reads the current value from the
 // settings table, so an administrator's change takes effect on the next tick
 // instead of at the next restart.
+//
+// Each pass runs under archiverLockKey (see withAdvisoryLock), so that on more
+// than one replica only whichever instance's tick takes the lock first actually
+// sweeps; the rest skip that tick rather than racing the same pass.
 func StartArchiver(ctx context.Context, db *sql.DB, archiveAfter, staleAfter time.Duration, notify NotifyConfig) {
 	ticker := time.NewTicker(sweepInterval)
 	defer ticker.Stop()
 
-	Sweep(ctx, db, archiveAfter, staleAfter, notify)
+	sweep := func() {
+		withAdvisoryLock(ctx, db, archiverLockKey, "sweeper", func() {
+			Sweep(ctx, db, archiveAfter, staleAfter, notify)
+		})
+	}
+
+	sweep()
 	for {
 		select {
 		case <-ticker.C:
-			Sweep(ctx, db, archiveAfter, staleAfter, notify)
+			sweep()
 		case <-ctx.Done():
 			return
 		}
@@ -126,7 +142,7 @@ func expireStale(ctx context.Context, db *sql.DB, staleAfter time.Duration, skip
 			continue
 		}
 		alertID := id
-		if err := logEvent(ctx, db, incidentID, evAlertResolved, nil, &alertID, nil); err != nil {
+		if err := logEvent(ctx, db, incidentID, evAlertResolved, nil, nil, &alertID, nil); err != nil {
 			log.Printf("sweeper: log expiry event: %v", err)
 		}
 	}

internal/api/caller.go

@@ -99,13 +99,24 @@ func (c Caller) ServiceAccountID() (int64, bool) {
 	return c.sa.id, true
 }
 
+// ServiceAccountName reports this caller's own service-account name, for a
+// handler's synchronous response — the same credential it authenticated
+// with, already resolved onto the Caller by serveAsServiceAccount, so no
+// extra query is needed.
+func (c Caller) ServiceAccountName() (string, bool) {
+	if c.sa == nil {
+		return "", false
+	}
+	return c.sa.name, true
+}
+
 // Identity is a stable, log/audit-facing string distinguishing a human
 // caller from a service account — "user:42" or "service-account:7". Not
-// wired into any database column today (incidents.go's acknowledged_by/
-// assigned_to/user_id are explicitly out of scope for this change — that
-// needs its own schema migration, tracked separately), but this is the one
-// place in the request path that already knows which kind of caller this
-// is, and that follow-up will want exactly this accessor.
+// wired into any database column — incidents.go's acknowledged_by/
+// incident_events.user_id use AsHuman()/ServiceAccountID() directly against
+// the parallel *_service_account_id columns (migration 015) instead, since a
+// column needs the id, not this rendered string. assigned_to stays
+// human-only and out of scope (terdut-server#25's follow-up).
 func (c Caller) Identity() string {
 	switch {
 	case c.user != nil:

internal/api/deadman.go

@@ -373,7 +373,7 @@ func deadmanDied(ctx context.Context, db *sql.DB, notify NotifyConfig, hb deadma
 
 	alertID := hb.id
 	detail := "last heartbeat " + humanDuration(now.Sub(time.Unix(hb.receivedAt, 0))) + " ago"
-	if err := logEvent(ctx, tx, incidentID, evDeadmanSilent, nil, &alertID, &detail); err != nil {
+	if err := logEvent(ctx, tx, incidentID, evDeadmanSilent, nil, nil, &alertID, &detail); err != nil {
 		return err
 	}
 
@@ -415,7 +415,7 @@ func deadmanRecovered(ctx context.Context, db *sql.DB, hb deadmanAlert) error {
 		time.Now().Unix(), incidentResolutionRecovered, incidentID); err != nil {
 		return err
 	}
-	if err := logEvent(ctx, tx, incidentID, evResolved, nil, nil, nil); err != nil {
+	if err := logEvent(ctx, tx, incidentID, evResolved, nil, nil, nil, nil); err != nil {
 		return err
 	}
 	// The all-clear goes to whoever was paged, which enqueueResolved works out

internal/api/escalation.go

@@ -229,7 +229,7 @@ func advanceEscalation(ctx context.Context, db *sql.DB, cfg NotifyConfig, policy
 		// nobody. That is a policy that looks configured and is not.
 		detail += ": nobody reachable"
 	}
-	if err := logEvent(ctx, tx, incidentID, evEscalated, nil, nil, &detail); err != nil {
+	if err := logEvent(ctx, tx, incidentID, evEscalated, nil, nil, nil, &detail); err != nil {
 		return err
 	}
 	return tx.Commit()
@@ -256,7 +256,7 @@ func escalationExhausted(ctx context.Context, tx *sql.Tx, policy *escalationPoli
 		incidentID); err != nil {
 		return err
 	}
-	return logEvent(ctx, tx, incidentID, evEscalated, nil, nil, &detail)
+	return logEvent(ctx, tx, incidentID, evEscalated, nil, nil, nil, &detail)
 }
 
 // pageLevel notifies every target of one level and reports who was woken.

internal/api/helpers.go

@@ -1,8 +1,11 @@
 package api
 
 import (
+	"context"
+	"database/sql"
 	"encoding/json"
 	"errors"
+	"log"
 	"net/http"
 	"strconv"
 	"strings"
@@ -77,3 +80,39 @@ func decodeJSON(r *http.Request, v any) error {
 func errResp(msg string) map[string]string {
 	return map[string]string{"error": msg}
 }
+
+// withAdvisoryLock runs fn only if it can take the named Postgres advisory lock on a
+// dedicated connection, and skips fn otherwise. This is what keeps the archiver and
+// notifier safe to run on more than one replica: whichever instance's tick gets there
+// first does the work; the rest see the lock held and simply wait for their next tick
+// instead of running the same pass concurrently.
+//
+// pg_try_advisory_lock is session-scoped, so taking and releasing it must happen on the
+// same connection, reserved via db.Conn rather than borrowed from the pool's shared
+// connections fn itself may use — and released (unlocked, then closed) before returning,
+// since a session lock otherwise outlives this call and leaks onto whatever reuses the
+// pooled connection next.
+func withAdvisoryLock(ctx context.Context, db *sql.DB, key int64, name string, fn func()) {
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		log.Printf("%s: advisory lock: acquire connection: %v", name, err)
+		return
+	}
+	defer conn.Close()
+
+	var locked bool
+	if err := conn.QueryRowContext(ctx, "SELECT pg_try_advisory_lock($1)", key).Scan(&locked); err != nil {
+		log.Printf("%s: advisory lock: %v", name, err)
+		return
+	}
+	if !locked {
+		return // another replica is already running this pass
+	}
+	defer func() {
+		if _, err := conn.ExecContext(ctx, "SELECT pg_advisory_unlock($1)", key); err != nil {
+			log.Printf("%s: advisory unlock: %v", name, err)
+		}
+	}()
+
+	fn()
+}

internal/api/incident_store.go

@@ -65,11 +65,13 @@ const incidentSelectFrom = `
 	         WHERE el.team_id = i.team_id AND el.position = i.escalation_level),
 	       i.triggered_at,
 	       i.acknowledged_by, i.acknowledged_at, ack.username,
+	       i.acknowledged_by_service_account_id, acksa.name,
 	       i.assigned_to, asg.username, i.snoozed_until,
 	       i.resolved_at, i.resolution_source, i.archived_at
 	FROM   incidents i
 	JOIN   teams t ON t.id = i.team_id
 	LEFT   JOIN users ack ON ack.id = i.acknowledged_by
+	LEFT   JOIN service_accounts acksa ON acksa.id = i.acknowledged_by_service_account_id
 	LEFT   JOIN users asg ON asg.id = i.assigned_to`
 
 func scanIncident(s scanner) (models.Incident, error) {
@@ -83,6 +85,7 @@ func scanIncident(s scanner) (models.Incident, error) {
 		&i.EscalationLevel, &escalationDue,
 		&triggeredAt,
 		&i.AcknowledgedByID, &ackAt, &i.AcknowledgedByUser,
+		&i.AcknowledgedByServiceAccountID, &i.AcknowledgedByServiceAccountName,
 		&i.AssignedToID, &i.AssignedToUser, &snoozedUntil,
 		&resolvedAt, &i.ResolutionSource, &archivedAt,
 	); err != nil {
@@ -112,13 +115,31 @@ func fetchIncident(ctx context.Context, q querier, id int64) (models.Incident, e
 	return scanIncident(q.QueryRowContext(ctx, incidentSelectFrom+" WHERE i.id = $1", id))
 }
 
-// logEvent appends one entry to an incident's timeline. A nil userID means the
-// server acted rather than a person.
-func logEvent(ctx context.Context, q querier, incidentID int64, evType string, userID, alertID *int64, detail *string) error {
+// callerActorIDs resolves the current request's caller into the pair of
+// nilable ids logEvent/acknowledgeIncidentAs expect: exactly one of userID/
+// serviceAccountID is set (never both), replacing the unchecked
+// userFromContext(ctx) zero-value reads that used to write a human-only id
+// of 0 for a service-account caller (terdut-server#25).
+func callerActorIDs(ctx context.Context) (userID, serviceAccountID *int64) {
+	caller, _ := callerFromContext(ctx)
+	if u, ok := caller.AsHuman(); ok {
+		return &u.ID, nil
+	}
+	if id, ok := caller.ServiceAccountID(); ok {
+		return nil, &id
+	}
+	return nil, nil
+}
+
+// logEvent appends one entry to an incident's timeline. userID and
+// serviceAccountID are mutually exclusive and both nilable; both nil means
+// the server acted rather than any caller (see incident_events_actor_xor_chk,
+// migration 015).
+func logEvent(ctx context.Context, q querier, incidentID int64, evType string, userID, serviceAccountID, alertID *int64, detail *string) error {
 	_, err := q.ExecContext(ctx, `
-		INSERT INTO incident_events (incident_id, type, user_id, alert_id, detail, created_at)
-		VALUES ($1, $2, $3, $4, $5, $6)`,
-		incidentID, evType, userID, alertID, detail, time.Now().Unix())
+		INSERT INTO incident_events (incident_id, type, user_id, service_account_id, alert_id, detail, created_at)
+		VALUES ($1, $2, $3, $4, $5, $6, $7)`,
+		incidentID, evType, userID, serviceAccountID, alertID, detail, time.Now().Unix())
 	return err
 }
 
@@ -251,7 +272,7 @@ func resolveIfSettled(ctx context.Context, q querier, incidentID int64) (bool, e
 	if err := stopEscalation(ctx, q, incidentID); err != nil {
 		return false, err
 	}
-	if err := logEvent(ctx, q, incidentID, evResolved, nil, nil, nil); err != nil {
+	if err := logEvent(ctx, q, incidentID, evResolved, nil, nil, nil, nil); err != nil {
 		return false, err
 	}
 	// The all-clear goes only to whoever was paged in the first place, which
@@ -260,19 +281,30 @@ func resolveIfSettled(ctx context.Context, q querier, incidentID int64) (bool, e
 	return true, enqueueResolved(ctx, q, incidentID)
 }
 
-// acknowledgeIncident records that userID has picked an incident up, and reports
-// whether it changed anything — an already-resolved or already-acknowledged
-// incident is left alone, so a second acknowledge (a retried request, or a
-// stale push notification tapped after the web UI already acked it) is a
-// no-op rather than a second "acknowledged" timeline entry. Shared by the
-// authenticated handler and the Acknowledge button in a push notification,
-// so both write the same state and the same timeline entry.
+// acknowledgeIncident records that userID — a human — has picked an incident
+// up, and reports whether it changed anything — an already-resolved or
+// already-acknowledged incident is left alone, so a second acknowledge (a
+// retried request, or a stale push notification tapped after the web UI
+// already acked it) is a no-op rather than a second "acknowledged" timeline
+// entry. Used only by the Acknowledge button in a push notification
+// (notify_ack.go), which always resolves a human from
+// incident_ack_tokens.user_id — there is no service-account equivalent of
+// that flow, so this keeps its human-only signature; the authenticated
+// handler goes through acknowledgeIncidentAs below instead.
 func acknowledgeIncident(ctx context.Context, q querier, incidentID, userID int64) (bool, error) {
+	return acknowledgeIncidentAs(ctx, q, incidentID, &userID, nil)
+}
+
+// acknowledgeIncidentAs is acknowledgeIncident generalized to either actor
+// kind. userID and serviceAccountID are mutually exclusive and nilable the
+// same way logEvent's are (see incidents_ack_actor_xor_chk, migration 015).
+func acknowledgeIncidentAs(ctx context.Context, q querier, incidentID int64, userID, serviceAccountID *int64) (bool, error) {
 	res, err := q.ExecContext(ctx, `
 		UPDATE incidents
-		   SET status = 'acknowledged', acknowledged_by = $1, acknowledged_at = $2
-		 WHERE id = $3 AND status = 'triggered'`,
-		userID, time.Now().Unix(), incidentID)
+		   SET status = 'acknowledged', acknowledged_by = $1, acknowledged_by_service_account_id = $2,
+		       acknowledged_at = $3
+		 WHERE id = $4 AND status = 'triggered'`,
+		userID, serviceAccountID, time.Now().Unix(), incidentID)
 	if err != nil {
 		return false, err
 	}
@@ -283,7 +315,7 @@ func acknowledgeIncident(ctx context.Context, q querier, incidentID, userID int6
 	if err := stopEscalation(ctx, q, incidentID); err != nil {
 		return false, err
 	}
-	return true, logEvent(ctx, q, incidentID, evAcknowledged, &userID, nil, nil)
+	return true, logEvent(ctx, q, incidentID, evAcknowledged, userID, serviceAccountID, nil, nil)
 }
 
 // openIncidentForAlert returns the open incident an alert currently belongs to,

internal/api/incidents.go

@@ -157,9 +157,11 @@ func handleIncidentTimeline(db *sql.DB) http.HandlerFunc {
 
 		rows, err := db.QueryContext(r.Context(), `
 			SELECT e.id, e.incident_id, e.type, e.user_id, u.username,
+			       e.service_account_id, sa.name,
 			       e.alert_id, e.detail, e.created_at
 			FROM   incident_events e
 			LEFT   JOIN users u ON u.id = e.user_id
+			LEFT   JOIN service_accounts sa ON sa.id = e.service_account_id
 			WHERE  e.incident_id = $1
 			ORDER  BY e.created_at ASC, e.id ASC`, id)
 		if err != nil {
@@ -173,6 +175,7 @@ func handleIncidentTimeline(db *sql.DB) http.HandlerFunc {
 			var e models.IncidentEvent
 			var ts int64
 			if err := rows.Scan(&e.ID, &e.IncidentID, &e.Type, &e.UserID, &e.Username,
+				&e.ServiceAccountID, &e.ServiceAccountName,
 				&e.AlertID, &e.Detail, &ts); err != nil {
 				respond(w, http.StatusInternalServerError, errResp("internal error"))
 				return
@@ -190,8 +193,8 @@ func handleIncidentAcknowledge(db *sql.DB) http.HandlerFunc {
 		if !ok {
 			return
 		}
-		user, _ := userFromContext(r.Context())
-		acked, err := acknowledgeIncident(r.Context(), db, id, user.ID)
+		userID, saID := callerActorIDs(r.Context())
+		acked, err := acknowledgeIncidentAs(r.Context(), db, id, userID, saID)
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
@@ -223,13 +226,14 @@ func handleIncidentUnacknowledge(db *sql.DB) http.HandlerFunc {
 		if !ok {
 			return
 		}
-		user, _ := userFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		if !updateOpenIncident(w, r, db, id,
-			`UPDATE incidents SET status = 'triggered', acknowledged_by = NULL, acknowledged_at = NULL
+			`UPDATE incidents SET status = 'triggered', acknowledged_by = NULL,
+			        acknowledged_by_service_account_id = NULL, acknowledged_at = NULL
 			  WHERE id = $1 AND resolved_at IS NULL`, id) {
 			return
 		}
-		if err := logEvent(r.Context(), db, id, evUnacknowledged, &user.ID, nil, nil); err != nil {
+		if err := logEvent(r.Context(), db, id, evUnacknowledged, userID, saID, nil, nil); err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
@@ -247,7 +251,7 @@ func handleIncidentResolve(db *sql.DB) http.HandlerFunc {
 		if !ok {
 			return
 		}
-		user, _ := userFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		// The body is optional: clients that predate resolution notes send none.
 		var req struct {
 			Resolution string `json:"resolution"`
@@ -268,12 +272,12 @@ func handleIncidentResolve(db *sql.DB) http.HandlerFunc {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
-		if err := logEvent(r.Context(), db, id, evResolved, &user.ID, nil, nil); err != nil {
+		if err := logEvent(r.Context(), db, id, evResolved, userID, saID, nil, nil); err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
 		if req.Resolution != "" {
-			if err := logEvent(r.Context(), db, id, evResolutionNote, &user.ID, nil, &req.Resolution); err != nil {
+			if err := logEvent(r.Context(), db, id, evResolutionNote, userID, saID, nil, &req.Resolution); err != nil {
 				respond(w, http.StatusInternalServerError, errResp("internal error"))
 				return
 			}
@@ -312,7 +316,7 @@ func handleIncidentAssign(db *sql.DB) http.HandlerFunc {
 			return
 		}
 		// On an "assigned" event user_id is the assignee, not the actor.
-		if err := logEvent(r.Context(), db, id, evAssigned, &req.UserID, nil, nil); err != nil {
+		if err := logEvent(r.Context(), db, id, evAssigned, &req.UserID, nil, nil, nil); err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
@@ -363,14 +367,14 @@ func handleIncidentSnooze(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		user, _ := userFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		if !updateOpenIncident(w, r, db, id,
 			"UPDATE incidents SET snoozed_until = $1 WHERE id = $2 AND resolved_at IS NULL",
 			until.Unix(), id) {
 			return
 		}
 		detail := until.UTC().Format(time.RFC3339)
-		if err := logEvent(r.Context(), db, id, evSnoozed, &user.ID, nil, &detail); err != nil {
+		if err := logEvent(r.Context(), db, id, evSnoozed, userID, saID, nil, &detail); err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
@@ -384,12 +388,12 @@ func handleIncidentUnsnooze(db *sql.DB) http.HandlerFunc {
 		if !ok {
 			return
 		}
-		user, _ := userFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		if !updateOpenIncident(w, r, db, id,
 			"UPDATE incidents SET snoozed_until = NULL WHERE id = $1 AND resolved_at IS NULL", id) {
 			return
 		}
-		if err := logEvent(r.Context(), db, id, evUnsnoozed, &user.ID, nil, nil); err != nil {
+		if err := logEvent(r.Context(), db, id, evUnsnoozed, userID, saID, nil, nil); err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
@@ -466,27 +470,32 @@ func handleCreateNote(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		user, _ := userFromContext(r.Context())
+		caller, _ := callerFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		now := time.Now()
 		var eventID int64
 		err := db.QueryRowContext(r.Context(), `
-			INSERT INTO incident_events (incident_id, type, user_id, detail, created_at)
-			VALUES ($1, $2, $3, $4, $5)
-			RETURNING id`, id, noteType, user.ID, req.Content, now.Unix()).Scan(&eventID)
+			INSERT INTO incident_events (incident_id, type, user_id, service_account_id, detail, created_at)
+			VALUES ($1, $2, $3, $4, $5, $6)
+			RETURNING id`, id, noteType, userID, saID, req.Content, now.Unix()).Scan(&eventID)
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return
 		}
 
-		respond(w, http.StatusCreated, models.IncidentEvent{
+		resp := models.IncidentEvent{
 			ID:         eventID,
 			IncidentID: id,
 			Type:       noteType,
-			UserID:     &user.ID,
-			Username:   &user.Username,
 			Detail:     &req.Content,
 			CreatedAt:  now.UTC().Truncate(time.Second),
-		})
+		}
+		if u, ok := caller.AsHuman(); ok {
+			resp.UserID, resp.Username = &u.ID, &u.Username
+		} else if saName, ok := caller.ServiceAccountName(); ok {
+			resp.ServiceAccountID, resp.ServiceAccountName = saID, &saName
+		}
+		respond(w, http.StatusCreated, resp)
 	}
 }
 
@@ -504,11 +513,12 @@ func handleDeleteNote(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		user, _ := userFromContext(r.Context())
+		userID, saID := callerActorIDs(r.Context())
 		res, err := db.ExecContext(r.Context(), `
 			DELETE FROM incident_events
-			 WHERE id = $1 AND incident_id = $2 AND type IN ($3, $4) AND user_id = $5`,
-			eventID, id, evNote, evResolutionNote, user.ID)
+			 WHERE id = $1 AND incident_id = $2 AND type IN ($3, $4)
+			   AND (user_id = $5 OR service_account_id = $6)`,
+			eventID, id, evNote, evResolutionNote, userID, saID)
 		if err != nil {
 			respond(w, http.StatusInternalServerError, errResp("internal error"))
 			return

internal/api/incidents_test.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"git.ryuvia.com/niklas/terdut-server/internal/api"
+	"git.ryuvia.com/niklas/terdut-server/internal/models"
 )
 
 // amAlert builds one alert of a webhook payload.
@@ -642,6 +643,106 @@ func TestIncident_ArchiveRoundTrip(t *testing.T) {
 	}
 }
 
+// ---------------------------------------------------------------------------
+// Service accounts (terdut-server#25)
+// ---------------------------------------------------------------------------
+
+// TestServiceAccount_CanActOnItsTeamsIncidents is #25's regression test.
+// Before the fix: acknowledge/resolve/snooze/create-note each 500'd (writing
+// acknowledged_by/user_id = 0, violating the users(id) FK for a service
+// account), and delete-note silently matched zero rows (WHERE user_id = 0)
+// instead of deleting.
+func TestServiceAccount_CanActOnItsTeamsIncidents(t *testing.T) {
+	s := newTS(t)
+	instanceKey := createServiceAccount(t, s, s.key, "operator", models.ServiceAccountScopeInstance, 0)
+	teamA := createTeamAs(t, s, instanceKey, "team-a")
+	keyA := createServiceAccount(t, s, instanceKey, "team-a-sa", models.ServiceAccountScopeTeam, teamA)
+
+	var integration struct {
+		Key string `json:"key"`
+	}
+	decode(t, s.reqAs(t, keyA, http.MethodPost, "/api/teams/"+id64(teamA)+"/integrations",
+		map[string]string{"name": "test"}), &integration)
+	postToIntegration(t, s, integration.Key, "fp-sa", "SAIncident") // incident 1
+
+	// Acknowledge.
+	resp := s.reqAs(t, keyA, http.MethodPost, "/api/incidents/1/acknowledge", nil)
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("service account acknowledge: %d", resp.StatusCode)
+	}
+	var inc map[string]any
+	decode(t, resp, &inc)
+	if inc["acknowledged_by_service_account_id"] == nil {
+		t.Error("expected acknowledged_by_service_account_id to be set")
+	}
+	if inc["acknowledged_by_id"] != nil {
+		t.Errorf("expected acknowledged_by_id to stay nil for a service-account actor, got %v", inc["acknowledged_by_id"])
+	}
+
+	// Unacknowledge.
+	resp = s.reqAs(t, keyA, http.MethodDelete, "/api/incidents/1/acknowledge", nil)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusNoContent {
+		t.Errorf("service account unacknowledge: %d", resp.StatusCode)
+	}
+
+	// Snooze, then unsnooze.
+	resp = s.reqAs(t, keyA, http.MethodPost, "/api/incidents/1/snooze",
+		map[string]string{"duration": "1h"})
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("service account snooze: %d", resp.StatusCode)
+	}
+	resp = s.reqAs(t, keyA, http.MethodDelete, "/api/incidents/1/snooze", nil)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusNoContent {
+		t.Errorf("service account unsnooze: %d", resp.StatusCode)
+	}
+
+	// Create, then delete, a note.
+	var note map[string]any
+	decode(t, s.reqAs(t, keyA, http.MethodPost, "/api/incidents/1/notes",
+		map[string]string{"content": "looking into it"}), &note)
+	if note["service_account_id"] == nil {
+		t.Error("expected service_account_id on the note event")
+	}
+	if note["user_id"] != nil {
+		t.Errorf("expected no user_id on a service-account note, got %v", note["user_id"])
+	}
+	noteID := int(note["id"].(float64))
+	delResp := s.reqAs(t, keyA, http.MethodDelete, fmt.Sprintf("/api/incidents/1/notes/%d", noteID), nil)
+	delResp.Body.Close()
+	if delResp.StatusCode != http.StatusNoContent {
+		t.Errorf("service account deleting its own note: %d", delResp.StatusCode)
+	}
+
+	// Resolve.
+	resp = s.reqAs(t, keyA, http.MethodPost, "/api/incidents/1/resolve", nil)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("service account resolve: %d", resp.StatusCode)
+	}
+}
+
+// Regression guard: a human actor must still write only the human columns,
+// unaffected by the service-account branch added above.
+func TestIncident_AcknowledgeStillWritesOnlyHumanColumn(t *testing.T) {
+	s := newTS(t)
+	postWebhook(t, s, []map[string]any{
+		amAlert("fp-human-ack", "Z", "firing", "2026-05-20T10:00:00Z", zeroTime, nil),
+	})
+
+	var inc map[string]any
+	decode(t, s.req(t, http.MethodPost, "/api/incidents/1/acknowledge", nil), &inc)
+	if inc["acknowledged_by_id"] == nil {
+		t.Error("expected acknowledged_by_id to be set for a human actor")
+	}
+	if inc["acknowledged_by_service_account_id"] != nil {
+		t.Errorf("expected acknowledged_by_service_account_id to stay nil for a human actor, got %v",
+			inc["acknowledged_by_service_account_id"])
+	}
+}
+
 func TestSweeper_ArchivesResolvedIncidents(t *testing.T) {
 	s := newTS(t)
 	postWebhook(t, s, []map[string]any{

internal/api/notifier.go

@@ -38,6 +38,13 @@ const (
 	ackTokenTTL = 24 * time.Hour
 )
 
+// notifierLockKey is the Postgres advisory lock the notifier takes for the
+// duration of each pass, so that running more than one replica does not
+// deliver (or double-deliver) the same notification from more than one of
+// them at once. Its value has no meaning beyond being distinct from
+// archiverLockKey.
+const notifierLockKey int64 = 7265_0002
+
 // Notification kinds, recording why a push was sent.
 const (
 	notifyTriggered = "triggered"
@@ -97,6 +104,10 @@ 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.
+//
+// Each pass runs under notifierLockKey (see withAdvisoryLock), so that on more
+// than one replica only whichever instance's tick takes the lock first actually
+// delivers; the rest skip that tick rather than racing the same pass.
 func StartNotifier(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
 	if !cfg.enabled() {
 		log.Print("notifier: disabled (no ntfy URL configured)")
@@ -107,11 +118,17 @@ func StartNotifier(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
 	ticker := time.NewTicker(notifyInterval)
 	defer ticker.Stop()
 
-	NotifySweep(ctx, db, cfg)
+	sweep := func() {
+		withAdvisoryLock(ctx, db, notifierLockKey, "notifier", func() {
+			NotifySweep(ctx, db, cfg)
+		})
+	}
+
+	sweep()
 	for {
 		select {
 		case <-ticker.C:
-			NotifySweep(ctx, db, cfg)
+			sweep()
 		case <-ctx.Done():
 			return
 		}
@@ -240,7 +257,7 @@ func deliverPending(ctx context.Context, db *sql.DB, cfg NotifyConfig) {
 		}
 		// 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 {
+		if err := logEvent(ctx, db, n.incidentID, eventNotified, n.userID, nil, nil, &n.kind); err != nil {
 			log.Printf("notifier: log delivery of %d: %v", n.id, err)
 		}
 		sent++
@@ -295,7 +312,7 @@ func markFailed(ctx context.Context, db *sql.DB, n outboxRow, cause error) {
 		return
 	}
 	detail := fmt.Sprintf("%s: %s", n.kind, cause)
-	if err := logEvent(ctx, db, n.incidentID, eventNotifyFailed, n.userID, nil, &detail); err != nil {
+	if err := logEvent(ctx, db, n.incidentID, eventNotifyFailed, n.userID, nil, nil, &detail); err != nil {
 		log.Printf("notifier: log failure of %d: %v", n.id, err)
 	}
 }

internal/db/db.go

@@ -1,6 +1,7 @@
 package db
 
 import (
+	"context"
 	"database/sql"
 	"embed"
 	"fmt"
@@ -62,6 +63,16 @@ func Open(dsn string) (*sql.DB, error) {
 	}
 }
 
+// migrationLockKey is the Postgres advisory lock Migrate holds for its whole
+// run. Two replicas starting at once would otherwise race the check-then-apply
+// loop below against schema_migrations: the loser could crash on a
+// duplicate-key insert, or contend with the winner's uncommitted DDL. Blocking
+// (pg_advisory_lock, not pg_try_advisory_lock as the archiver and notifier
+// use): on boot there is no later tick to defer to, so the right behaviour is
+// to wait for the other replica to finish migrating, not to skip ahead and
+// start serving against an unmigrated schema.
+const migrationLockKey int64 = 7265_0003
+
 // Migrate applies every embedded migration that has not been applied yet, in
 // filename order, recording each in schema_migrations.
 //
@@ -69,6 +80,22 @@ func Open(dsn string) (*sql.DB, error) {
 // migration that failed half way used to leave the schema in whatever state it
 // had reached. Postgres has transactional DDL, so the rollback is real.
 func Migrate(db *sql.DB) error {
+	ctx := context.Background()
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		return fmt.Errorf("migrate: acquire connection: %w", err)
+	}
+	defer conn.Close()
+
+	if _, err := conn.ExecContext(ctx, "SELECT pg_advisory_lock($1)", migrationLockKey); err != nil {
+		return fmt.Errorf("migrate: acquire advisory lock: %w", err)
+	}
+	defer func() {
+		if _, err := conn.ExecContext(ctx, "SELECT pg_advisory_unlock($1)", migrationLockKey); err != nil {
+			log.Printf("migrate: release advisory lock: %v", err)
+		}
+	}()
+
 	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
 		version    TEXT PRIMARY KEY,
 		applied_at BIGINT NOT NULL DEFAULT FLOOR(EXTRACT(EPOCH FROM now()))::bigint

internal/db/db_test.go

@@ -0,0 +1,125 @@
+package db_test
+
+import (
+	"database/sql"
+	"fmt"
+	"net/url"
+	"os"
+	"strings"
+	"sync"
+	"testing"
+
+	"git.ryuvia.com/niklas/terdut-server/internal/db"
+
+	_ "github.com/jackc/pgx/v5/stdlib"
+)
+
+// TERDUT_TEST_DSN must point at a database the test role may create schemas
+// in; see internal/api/testdb_test.go for the fuller rationale this mirrors.
+// An unset DSN fails rather than skips, deliberately.
+const testDSNEnv = "TERDUT_TEST_DSN"
+
+// TestMigrate_ConcurrentCallersDoNotRace reproduces two replicas starting at
+// once against a brand-new, unmigrated schema: both call db.Migrate at the
+// same time. Before migrationLockKey, the loser could crash on a
+// duplicate-key insert into schema_migrations, or contend with the winner's
+// uncommitted DDL; with the advisory lock, one blocks until the other
+// finishes and both return cleanly.
+func TestMigrate_ConcurrentCallersDoNotRace(t *testing.T) {
+	dsn := os.Getenv(testDSNEnv)
+	if dsn == "" {
+		t.Fatalf("%s is not set: these tests need Postgres.\n"+
+			"Run `make test-db` for a local one, then\n"+
+			"  export %s=postgres://terdut:terdut@localhost:5432/terdut_test?sslmode=disable",
+			testDSNEnv, testDSNEnv)
+	}
+
+	schema := fmt.Sprintf("migrate_race_%d", os.Getpid())
+	admin, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatalf("connect to %s: %v", testDSNEnv, err)
+	}
+	defer admin.Close()
+	if _, err := admin.Exec("CREATE SCHEMA " + schema); err != nil {
+		t.Fatalf("create schema %s: %v", schema, err)
+	}
+	t.Cleanup(func() {
+		cleanup, err := sql.Open("pgx", dsn)
+		if err != nil {
+			return
+		}
+		defer cleanup.Close()
+		if _, err := cleanup.Exec("DROP SCHEMA " + schema + " CASCADE"); err != nil {
+			t.Logf("drop schema %s: %v", schema, err)
+		}
+	})
+
+	scoped := withSearchPath(dsn, schema)
+
+	const callers = 2
+	errs := make([]error, callers)
+	var wg sync.WaitGroup
+	for i := range callers {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			database, err := db.Open(scoped)
+			if err != nil {
+				errs[i] = fmt.Errorf("open: %w", err)
+				return
+			}
+			defer database.Close()
+			errs[i] = db.Migrate(database)
+		}(i)
+	}
+	wg.Wait()
+
+	for i, err := range errs {
+		if err != nil {
+			t.Fatalf("Migrate #%d: %v", i, err)
+		}
+	}
+
+	entries, err := os.ReadDir("migrations")
+	if err != nil {
+		t.Fatalf("read migrations dir: %v", err)
+	}
+	var want int
+	for _, e := range entries {
+		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
+			want++
+		}
+	}
+
+	check, err := sql.Open("pgx", scoped)
+	if err != nil {
+		t.Fatalf("connect for verification: %v", err)
+	}
+	defer check.Close()
+
+	var got int
+	if err := check.QueryRow("SELECT COUNT(*) FROM schema_migrations").Scan(&got); err != nil {
+		t.Fatalf("count schema_migrations: %v", err)
+	}
+	if got != want {
+		t.Fatalf("schema_migrations has %d row(s) after two concurrent Migrate calls, want %d (one per migration file, no duplicates)", got, want)
+	}
+}
+
+// withSearchPath pins a DSN to one schema. Copied from
+// internal/api/testdb_test.go rather than shared: that helper lives in the
+// api_test package, a separate compiled package this one cannot import.
+func withSearchPath(dsn, schema string) string {
+	opt := "-csearch_path=" + schema
+
+	if strings.HasPrefix(dsn, "postgres://") || strings.HasPrefix(dsn, "postgresql://") {
+		u, err := url.Parse(dsn)
+		if err == nil {
+			q := u.Query()
+			q.Set("options", opt)
+			u.RawQuery = q.Encode()
+			return u.String()
+		}
+	}
+	return dsn + " options='" + opt + "'"
+}

internal/db/migrations/015_incident_service_account_actors.sql

@@ -0,0 +1,39 @@
+-- Service-account actors on incident mutations (terdut-server#25). A
+-- team-scoped service account acknowledging/resolving/snoozing/noting an
+-- incident is not a users row, so it cannot be written into
+-- acknowledged_by/incident_events.user_id — doing so either violates the
+-- users(id) FK (new rows) or, for incident_events.user_id, silently matches
+-- zero rows on delete. These columns are the service-account-shaped parallel
+-- to the existing human ones: nullable, mutually exclusive with their human
+-- counterpart, ON DELETE SET NULL so a deleted service account doesn't take
+-- the incident history with it.
+ALTER TABLE incidents
+    ADD COLUMN acknowledged_by_service_account_id BIGINT
+        REFERENCES service_accounts(id) ON DELETE SET NULL;
+
+ALTER TABLE incident_events
+    ADD COLUMN service_account_id BIGINT
+        REFERENCES service_accounts(id) ON DELETE SET NULL;
+
+-- At most one actor kind per row: both NULL ("the server acted") is valid,
+-- exactly one set is valid, both set is a bug this constraint refuses to
+-- store rather than silently accepting.
+ALTER TABLE incidents
+    ADD CONSTRAINT incidents_ack_actor_xor_chk CHECK (
+        acknowledged_by IS NULL OR acknowledged_by_service_account_id IS NULL
+    );
+
+ALTER TABLE incident_events
+    ADD CONSTRAINT incident_events_actor_xor_chk CHECK (
+        user_id IS NULL OR service_account_id IS NULL
+    );
+
+CREATE INDEX incidents_acknowledged_by_service_account_id_idx
+    ON incidents(acknowledged_by_service_account_id);
+CREATE INDEX incident_events_service_account_id_idx
+    ON incident_events(service_account_id);
+
+-- assigned_to_service_account_id is deliberately not added here: it would sit
+-- unpopulated until handleIncidentAssign itself tracks an actor, which is a
+-- separate, pre-existing gap (it records the assignee today, never the
+-- actor, for humans either) tracked in its own follow-up issue.

internal/models/incident.go

@@ -43,6 +43,13 @@ type Incident struct {
 	AcknowledgedByUser *string    `json:"acknowledged_by,omitempty"`
 	AcknowledgedAt     *time.Time `json:"acknowledged_at,omitempty"`
 
+	// AcknowledgedByServiceAccountID/Name are the service-account-shaped
+	// parallel to AcknowledgedByID/User above: mutually exclusive with it,
+	// populated when a service account (not a human) acknowledged this
+	// incident. See migration 015 and terdut-server#25.
+	AcknowledgedByServiceAccountID   *int64  `json:"acknowledged_by_service_account_id,omitempty"`
+	AcknowledgedByServiceAccountName *string `json:"acknowledged_by_service_account,omitempty"`
+
 	AssignedToID   *int64  `json:"assigned_to_id,omitempty"`
 	AssignedToUser *string `json:"assigned_to,omitempty"`
 
@@ -67,17 +74,27 @@ type Incident struct {
 // and is the only history this server keeps — alert rows are mutated in place.
 //
 // Type is one of: triggered, alert_added, alert_resolved, acknowledged,
-// unacknowledged, assigned, snoozed, unsnoozed, resolved, note. A nil UserID
-// means the server acted rather than a person.
+// unacknowledged, assigned, snoozed, unsnoozed, resolved, note. UserID and
+// ServiceAccountID are mutually exclusive; both nil means the server acted
+// rather than any caller.
 type IncidentEvent struct {
-	ID         int64     `json:"id"`
-	IncidentID int64     `json:"incident_id"`
-	Type       string    `json:"type"`
-	UserID     *int64    `json:"user_id,omitempty"`
-	Username   *string   `json:"username,omitempty"`
-	AlertID    *int64    `json:"alert_id,omitempty"`
-	Detail     *string   `json:"detail,omitempty"`
-	CreatedAt  time.Time `json:"created_at"`
+	ID         int64   `json:"id"`
+	IncidentID int64   `json:"incident_id"`
+	Type       string  `json:"type"`
+	UserID     *int64  `json:"user_id,omitempty"`
+	Username   *string `json:"username,omitempty"`
+
+	// ServiceAccountID/Name are the service-account-shaped parallel to
+	// UserID/Username above: mutually exclusive with it, populated when a
+	// service account (not a human, and not nil-meaning-the-server-acted)
+	// performed this event. Named Name, not Username — a ServiceAccount has
+	// a Name field, not a Username. See migration 015 and terdut-server#25.
+	ServiceAccountID   *int64  `json:"service_account_id,omitempty"`
+	ServiceAccountName *string `json:"service_account_name,omitempty"`
+
+	AlertID   *int64    `json:"alert_id,omitempty"`
+	Detail    *string   `json:"detail,omitempty"`
+	CreatedAt time.Time `json:"created_at"`
 }
 
 // SimilarIncident is an earlier, resolved incident with the same signature as

internal/web/static/app.css

@@ -326,6 +326,7 @@ input:focus, textarea:focus { outline: none; border-color: var(--accent); box-sh
 /* ---------- chips ---------- */
 
 .chips {
+  position: relative;
   display: flex; gap: 6px;
   padding: 12px 16px 8px;
   overflow-x: auto; scrollbar-width: none;
@@ -341,11 +342,14 @@ input:focus, textarea:focus { outline: none; border-color: var(--accent); box-sh
 }
 .chip[aria-selected="true"] { background: var(--text); border-color: var(--text); color: var(--bg); }
 .chip .count { margin-left: 4px; opacity: 0.7; }
-/* Pinned to the visible right edge of the scrolling row (sticky, not
-   absolute, so it tracks the scroll position rather than the content). */
+/* An overlay, not a flex item: absolute against .chips' own (non-scrolling)
+   box stays flush with its real right edge regardless of scroll position,
+   which turned out not to be true of position:sticky here — as a flex
+   item, its sticky offset interacted with the row's gap and its own
+   negative margin, landing short of the edge by about one gap's width. */
 .chips-fade {
-  position: sticky; right: -1px; flex: none;
-  width: 24px; margin-left: -24px;
+  position: absolute; top: 0; right: 0; bottom: 0;
+  width: 24px;
   background: linear-gradient(to right, transparent, var(--bg));
   pointer-events: none;
 }
@@ -579,6 +583,10 @@ details[open] > summary { margin-bottom: 8px; }
 }
 .actionbar .btn { min-height: 48px; }
 .actionbar .btn-primary { flex: 1; font-size: 16px; }
+/* The extra actions that only phones hide behind "More" — see actionBar() and
+   extraActions() in incident.js. Hidden by default; the desktop block below
+   shows them and hides the now-redundant More button instead. */
+.action-extra { display: none; }
 
 .detail-placeholder {
   display: grid; place-items: center; height: 100%;
@@ -665,7 +673,7 @@ details[open] > summary { margin-bottom: 8px; }
    caught by the unrelated .label > span styling meant for label chips. */
 .week-nav .week-label { font-size: 14px; font-weight: 650; min-width: 11.5em; text-align: center; white-space: nowrap; }
 .week-label small { color: var(--faint); font-weight: 600; font-size: 11px; margin-left: 2px; }
-.days { list-style: none; margin: 0; padding: 0; }
+.days { list-style: none; margin: 0 auto; padding: 0; }
 .day { display: grid; grid-template-columns: 3.2em 4.2em 1fr; align-items: center; gap: 8px; min-height: 50px; padding: 0 14px; }
 .day + .day { border-top: 1px solid var(--border); }
 .day-name { font-weight: 650; }
@@ -769,7 +777,15 @@ kbd {
   .pane-list .chips { flex-wrap: wrap; overflow-x: visible; }
   .pane-list .chip-sep { display: none; }
   .chips-fade { display: none; }
-  .view-queue:not(.has-detail) .pane-detail { display: block; }
+  /* With nothing selected there is no detail to show next to, so the list
+     takes the whole row instead of leaving the second column as dead space
+     around the placeholder text. Selecting an incident (.has-detail) drops
+     back to the base minmax(340,420) 1fr rule above. */
+  .view-queue:not(.has-detail) { grid-template-columns: 1fr; }
+  .view-queue:not(.has-detail) .pane-list { border-right: 0; }
+  /* Full width reads better capped than edge-to-edge on a very wide monitor,
+     matching .detail's own cap below. */
+  .view-queue:not(.has-detail) .list { max-width: 900px; margin: 0 auto; }
 
   /* On desktop the list stays visible next to the detail. */
   .app.detail-open .nav { display: flex; }
@@ -783,8 +799,12 @@ kbd {
   .actionbar {
     position: sticky; bottom: 0;
     padding: 12px 32px;
+    flex-wrap: wrap;
   }
   .actionbar .btn-primary { flex: 0 1 240px; }
+  /* Room enough to show every action, so More is fully redundant here. */
+  .action-extra { display: inline-flex; }
+  .more-btn { display: none; }
 
   .sheet {
     width: min(440px, calc(100% - 32px));

internal/web/static/js/account.js

@@ -33,7 +33,9 @@ function render() {
       h('div', { class: 'card' }, shortcuts())),
 
     h('div', { class: 'page-head' }),
-    h('button', { class: 'btn btn-block', type: 'button', onclick: signOut }, icon('logout'), 'Sign out'),
+    // Wrapped in a div: .btn is inline-flex, and only a block-level element
+    // picks up .view-page > *'s margin:auto centering (see app.css:316).
+    h('div', {}, h('button', { class: 'btn btn-block', type: 'button', onclick: signOut }, icon('logout'), 'Sign out')),
   );
 }
 

internal/web/static/js/adminteam.js

@@ -96,7 +96,9 @@ function render() {
 }
 
 function backLink() {
-  return h('a', { class: 'back-link', href: '/admin/teams' }, icon('chevronLeft'), h('span', { text: 'Teams' }));
+  // Wrapped in a div: .back-link is inline-flex, and only a block-level
+  // element picks up .view-page > *'s margin:auto centering (app.css:316).
+  return h('div', {}, h('a', { class: 'back-link', href: '/admin/teams' }, icon('chevronLeft'), h('span', { text: 'Teams' })));
 }
 
 // --- identity --------------------------------------------------------------

internal/web/static/js/adminuser.js

@@ -83,7 +83,9 @@ function render() {
 }
 
 function backLink() {
-  return h('a', { class: 'back-link', href: '/admin/users' }, icon('chevronLeft'), h('span', { text: 'Users' }));
+  // Wrapped in a div: .back-link is inline-flex, and only a block-level
+  // element picks up .view-page > *'s margin:auto centering (app.css:316).
+  return h('div', {}, h('a', { class: 'back-link', href: '/admin/users' }, icon('chevronLeft'), h('span', { text: 'Users' })));
 }
 
 // --- identity --------------------------------------------------------------

internal/web/static/js/incident.js

@@ -123,6 +123,16 @@ function who(id, name) {
   return name || 'someone';
 }
 
+// ackActorLabel renders whoever acknowledged inc, human or service account —
+// the two are mutually exclusive (migration 015), and a service account is a
+// credential, not "you" or "nobody", so it gets its own branch rather than
+// going through who()'s id-vs-myID() check.
+function ackActorLabel() {
+  if (inc.acknowledged_by_id != null) return who(inc.acknowledged_by_id, inc.acknowledged_by);
+  if (inc.acknowledged_by_service_account_id != null) return inc.acknowledged_by_service_account || 'a service account';
+  return null;
+}
+
 function facts() {
   const rows = [];
   const add = (k, ...v) => rows.push(h('dt', { text: k }), h('dd', {}, ...v));
@@ -132,8 +142,7 @@ function facts() {
   // take reading top to bottom to piece together.
   const elapsedTo = inc.resolved_at ? Date.parse(inc.resolved_at) : Date.now();
   const responsible = inc.assigned_to_id != null ? who(inc.assigned_to_id, inc.assigned_to)
-    : inc.acknowledged_by_id != null ? who(inc.acknowledged_by_id, inc.acknowledged_by)
-      : 'Unassigned';
+    : ackActorLabel() || 'Unassigned';
   rows.push(h('dt', { text: 'At a glance' }), h('dd', { class: 'fact-summary' },
     h('span', { class: 'fact-chip' }, icon('clock', 'icon fact-icon'), duration(elapsedTo - Date.parse(inc.triggered_at))),
     inc.severity && badge(inc.severity, `plain ${severityClass(inc.severity)}`),
@@ -142,7 +151,7 @@ function facts() {
 
   add('Triggered', when(inc.triggered_at), h('span', { class: 'sub', text: ` · ${ago(inc.triggered_at)}` }));
   if (inc.acknowledged_at) {
-    add('Acknowledged', `${who(inc.acknowledged_by_id, inc.acknowledged_by)} · ${when(inc.acknowledged_at)}`);
+    add('Acknowledged', `${ackActorLabel()} · ${when(inc.acknowledged_at)}`);
   }
   add('Assigned', inc.assigned_to_id != null ? who(inc.assigned_to_id, inc.assigned_to) : 'Unassigned');
   if (inc.status !== 'resolved' && isFuture(inc.snoozed_until)) {
@@ -206,9 +215,19 @@ function alertItem(a) {
 
 // ---------- timeline ----------
 
+// actorLabel renders whoever performed ev, human or service account — the
+// two are mutually exclusive (migration 015). null means the server acted:
+// ev.user_id == null no longer means that by itself, now that a service
+// account's events also leave it null.
+function actorLabel(ev, named = false) {
+  if (ev.user_id != null) return named ? (ev.username || 'someone') : who(ev.user_id, ev.username);
+  if (ev.service_account_id != null) return ev.service_account_name || 'a service account';
+  return null;
+}
+
 // named spells users out instead of "you", for text that leaves this page.
 function eventText(ev, named = false) {
-  const person = ev.user_id != null ? (named ? ev.username || 'someone' : who(ev.user_id, ev.username)) : null;
+  const person = actorLabel(ev, named);
   const strong = (t) => h('span', { class: 'who', text: t || 'someone' });
   const alertName = () => {
     const a = (inc.alerts || []).find((x) => x.id === ev.alert_id);
@@ -453,9 +472,25 @@ function quickActions() {
   return div;
 }
 
+// Desktop has room to show what a phone folds into the More sheet below — see
+// the .action-extra/.more-btn rules in app.css. Resolved/archived incidents
+// already say everything via primaryAction()/secondaryAction(), so there is
+// nothing extra to surface for them.
+function extraActions() {
+  if (!isOpen()) return [];
+  const out = [
+    h('button', { class: 'btn btn-sm action-extra', type: 'button', onclick: assign }, icon('user'), 'Assign…'),
+    h('button', { class: 'btn btn-sm action-extra', type: 'button', onclick: addNote }, icon('note'), 'Add note…'),
+  ];
+  out.push(inc.status === 'acknowledged'
+    ? h('button', { class: 'btn btn-sm action-extra', type: 'button', onclick: unacknowledge }, icon('undo'), 'Clear ack')
+    : h('button', { class: 'btn btn-sm action-extra', type: 'button', onclick: resolve }, icon('checkCircle'), 'Resolve…'));
+  return out;
+}
+
 function actionBar() {
-  const more = h('button', { class: 'btn', type: 'button', 'aria-label': 'More actions', onclick: moreMenu }, icon('more'), 'More');
-  const bar = h('div', { class: 'actionbar' }, primaryAction(), secondaryAction(), more);
+  const more = h('button', { class: 'btn more-btn', type: 'button', 'aria-label': 'More actions', onclick: moreMenu }, icon('more'), 'More');
+  const bar = h('div', { class: 'actionbar' }, primaryAction(), secondaryAction(), ...extraActions(), more);
   if (busy) for (const b of bar.querySelectorAll('button')) b.disabled = true;
   return bar;
 }