Show notes from similar earlier incidents

Each incident gets a signature: the alert name plus the group labels that
say what is broken, minus the ones that only say where it ran (instance,
pod, container, ...). GET /api/incidents/{id}/similar returns resolved
incidents in the same team with the same signature that have notes.

Notes can be marked as the resolution note, "what fixed it", either with a
resolution field on resolve or pinned on a note. Those lead the similar
list, show on the incident page as "Seen before", and the triggered
notification carries the latest one.

Claude-Session: https://claude.ai/code/session_01MMados3BD1oSjevHxbmVqU

internal/api/notifier.go

@@ -330,6 +330,16 @@ func deliver(ctx context.Context, db *sql.DB, cfg NotifyConfig, n outboxRow) err
 
 	msg := renderNotification(inc, n, firing, cfg)
 
+	// The page that opens an incident carries what fixed it last time, so the
+	// person woken up starts from that. Best effort: a failed lookup must not
+	// hold back the page itself.
+	if n.kind == notifyTriggered {
+		if sim, err := similarIncidents(ctx, db, n.incidentID, 1); err == nil && len(sim) > 0 && len(sim[0].ResolutionNotes) > 0 {
+			notes := sim[0].ResolutionNotes
+			msg.Message += "\nLast time: " + shorten(derefString(notes[len(notes)-1].Detail), 160)
+		}
+	}
+
 	// 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.
@@ -573,6 +583,17 @@ func plural(n int) string {
 	return "s"
 }
 
+// shorten cuts s to at most n runes, marking the cut, and flattens newlines so
+// a multi-line note stays one line in a push.
+func shorten(s string, n int) string {
+	s = strings.Join(strings.Fields(s), " ")
+	r := []rune(s)
+	if len(r) <= n {
+		return s
+	}
+	return string(r[:n-1]) + "…"
+}
+
 // derefString reads a nullable text column as a plain string.
 func derefString(s *string) string {
 	if s == nil {