Phase 3: dashboards and alerting

Saved, shareable multi-panel dashboards (table/line/bar/single-stat
panels via gridstack + uPlot, global + per-panel time range, JSON
export/import) and threshold/absence alert rules with an
ok/pending/firing evaluator and webhook/Slack/PagerDuty delivery.

- New /metadata component: Postgres control-plane store for dashboards,
  panels, notification targets, alert rules/state, and delivery log --
  see docs/phase-3-dashboard-design.md for why ClickHouse's MergeTree
  family isn't a fit for this access pattern (needs real row-level
  locking and read-your-writes consistency).
- api/internal/dashboards: dashboard/panel CRUD, pure -- panel query
  execution stays client-side, reusing the existing /query endpoint.
- New /alerting service: rule/target CRUD, a ticker-driven evaluator
  (claim-then-evaluate concurrency control, transactional-outbox
  delivery, query errors and threshold zero-rows never coerced into a
  false transition) and webhook/Slack/PagerDuty delivery with
  retry/backoff. See docs/phase-3-alerting-design.md for the full
  state-machine design and the four correctness properties it
  implements.
- web: /dashboards and /alerts UIs; cli: sentryctl dashboards/alerts
  list/get/apply, seeding a future Terraform provider's JSON contract.
- hack/alert-load-test: 500 rules against real ClickHouse data, real
  measured results in docs/phase-3-runbook.md.

Five real bugs found by actually running this against a live stack
(documented in the runbook, not just fixed silently): a latent Phase 2
bug where ClickHouse rejected the timestamp format used for
earliest=/latest= queries; a "now" literal token injected into query
text; a GridStack/uPlot layout-timing race; JS's Date.parse being too
lenient to use as a timestamp-detection heuristic; a rule's "enabled"
field silently defaulting to false when omitted; and the evaluator's
claim-batch-size and worker-pool-concurrency defaulting to the same
value, causing 500 concurrently-due rules to take 125s to cycle through
instead of the configured 60s.

api/internal/queryapi/handler.go

@@ -24,38 +24,24 @@ import (
 )
 
 type Handler struct {
-	logger        *slog.Logger
-	sqlRunner     executor.SQLRunner
-	search        executor.SearchClient
-	queryTimeout  time.Duration
-	allowedOrigin string
+	logger       *slog.Logger
+	sqlRunner    executor.SQLRunner
+	search       executor.SearchClient
+	queryTimeout time.Duration
 }
 
-func NewHandler(logger *slog.Logger, sqlRunner executor.SQLRunner, search executor.SearchClient, queryTimeout time.Duration, allowedOrigin string) *Handler {
-	return &Handler{logger: logger, sqlRunner: sqlRunner, search: search, queryTimeout: queryTimeout, allowedOrigin: allowedOrigin}
+func NewHandler(logger *slog.Logger, sqlRunner executor.SQLRunner, search executor.SearchClient, queryTimeout time.Duration) *Handler {
+	return &Handler{logger: logger, sqlRunner: sqlRunner, search: search, queryTimeout: queryTimeout}
 }
 
-func (h *Handler) Routes() http.Handler {
-	mux := http.NewServeMux()
+// RegisterRoutes adds this handler's routes onto a shared mux. Phase 3
+// introduced a second handler package (internal/dashboards), so CORS is
+// now applied once, by main.go, around the fully-assembled mux rather
+// than by each handler wrapping itself individually -- see
+// httpserver.WithCORS.
+func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("POST /query", h.handleQuery)
 	mux.HandleFunc("GET /healthz", h.handleHealthz)
-	return h.withCORS(mux)
-}
-
-// withCORS is deliberately permissive by default (see CORSAllowedOrigin in
-// internal/config) since there's no auth yet and the SvelteKit dev server
-// runs on a different origin. Tighten alongside adding real auth.
-func (h *Handler) withCORS(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.Header().Set("Access-Control-Allow-Origin", h.allowedOrigin)
-		w.Header().Set("Access-Control-Allow-Methods", "POST, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
-		next.ServeHTTP(w, r)
-	})
 }
 
 func (h *Handler) handleHealthz(w http.ResponseWriter, _ *http.Request) {