Show similar earlier incidents and let notes be marked as the fix

The incident view gets a "Seen before" section from the server's new
/similar endpoint; an older server without it just shows nothing. C adds a
note as the resolution note, alongside c for a plain note. Needs the
server release that adds /similar.

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

internal/api/client.go

@@ -276,6 +276,18 @@ func (c *Client) GetIncidentTimeline(id int64) ([]IncidentEvent, error) {
 	return events, c.do(req, &events)
 }
 
+// GetSimilarIncidents lists earlier resolved incidents that look like this one
+// and have notes. Servers before the similar-incidents endpoint answer 404; the
+// caller treats any error as "nothing to show".
+func (c *Client) GetSimilarIncidents(id int64) ([]SimilarIncident, error) {
+	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/incidents/%d/similar", id))
+	if err != nil {
+		return nil, err
+	}
+	var similar []SimilarIncident
+	return similar, c.do(req, &similar)
+}
+
 func (c *Client) AcknowledgeIncident(id int64) (*Incident, error) {
 	req, err := c.newRequest(http.MethodPost, fmt.Sprintf("/api/incidents/%d/acknowledge", id))
 	if err != nil {
@@ -357,10 +369,11 @@ func (c *Client) UnarchiveIncident(id int64) error {
 	return c.do(req, nil)
 }
 
-// AddNote appends a note to the incident's timeline.
-func (c *Client) AddNote(incidentID int64, content string) (*IncidentEvent, error) {
+// AddNote appends a note to the incident's timeline. pinned files it as the
+// resolution note: what fixed the incident, shown on similar ones later.
+func (c *Client) AddNote(incidentID int64, content string, pinned bool) (*IncidentEvent, error) {
 	req, err := c.newRequestWithBody(http.MethodPost,
-		fmt.Sprintf("/api/incidents/%d/notes", incidentID), map[string]string{"content": content})
+		fmt.Sprintf("/api/incidents/%d/notes", incidentID), map[string]any{"content": content, "pinned": pinned})
 	if err != nil {
 		return nil, err
 	}

internal/api/client_test.go

@@ -165,8 +165,10 @@ func TestClient_IncidentEndpoints(t *testing.T) {
 			http.MethodPost, "/api/incidents/7/archive", ""},
 		{"unarchive", func(c *Client) error { return c.UnarchiveIncident(7) },
 			http.MethodDelete, "/api/incidents/7/archive", ""},
-		{"add note", func(c *Client) error { _, err := c.AddNote(7, "hi"); return err },
+		{"add note", func(c *Client) error { _, err := c.AddNote(7, "hi", false); return err },
 			http.MethodPost, "/api/incidents/7/notes", ""},
+		{"similar", func(c *Client) error { _, err := c.GetSimilarIncidents(7); return err },
+			http.MethodGet, "/api/incidents/7/similar", `[]`},
 		{"delete note", func(c *Client) error { return c.DeleteNote(7, 12) },
 			http.MethodDelete, "/api/incidents/7/notes/12", ""},
 		{"stats", func(c *Client) error { _, err := c.GetIncidentStats(); return err },

internal/api/types.go

@@ -108,6 +108,10 @@ const (
 	EventResolved       = "resolved"
 	EventNote           = "note"
 
+	// A note marked as what fixed the incident. The server leads similar
+	// incidents with these.
+	EventResolutionNote = "resolution_note"
+
 	// Written when a team's dead man's switch stops reporting.
 	EventDeadmanSilent = "deadman_silent"
 
@@ -249,3 +253,15 @@ type APIKey struct {
 	CreatedAt  time.Time  `json:"created_at"`
 	LastUsedAt *time.Time `json:"last_used_at"`
 }
+
+// SimilarIncident is an earlier, resolved incident with the same signature
+// (alert name plus stable group labels) as the one being viewed. ResolutionNotes
+// are its "what fixed it" notes; NoteCount counts its plain notes.
+type SimilarIncident struct {
+	ID              int64           `json:"id"`
+	Title           string          `json:"title"`
+	TriggeredAt     time.Time       `json:"triggered_at"`
+	ResolvedAt      time.Time       `json:"resolved_at"`
+	NoteCount       int             `json:"note_count"`
+	ResolutionNotes []IncidentEvent `json:"resolution_notes"`
+}