fix(ingestion): bump mcp-chassis to v0.7.1; label refused REST requests by route

1. Rejections are logged. chassis v0.2.0 refused without a log line, so
   since #149 an unknown REST caller got silent 401s. v0.7.1 writes
   `mcp auth rejected` (reason, remote, token fingerprint, path) and
   `mcp auth accepted` per authenticated request. Tested through
   buildMux.

2. Fallout: since chassis v0.7 (mcp-chassis#4) NewJWTValidator no longer
   fails on OIDC discovery; the issuer resolves lazily and a JWT gets
   503-and-retry until it does. #83's boot retry loop therefore never
   retried, and its tests failed. buildJWTValidator now builds once and
   logs an issuer still unresolved at boot. Behaviour change: a
   misconfigured issuer no longer exits the process; JWTs get 503, the
   static bearer keeps working. internal/startupretry is now unused.

3. Metrics: authenticated REST requests were already labelled by route
   (the REST mux sets Pattern on the same *http.Request the middleware
   reads). Requests refused by auth never reached the REST mux and were
   labelled path="/". labelRESTPattern now sets the REST route's pattern
   before auth; unmatched paths keep "/", so the label set stays bounded.

Closes #155

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/cmd/server/routes.go

@@ -73,5 +73,19 @@ func mountREST(mux *http.ServeMux, h *api.Handler, auth func(http.Handler) http.
 	rest.HandleFunc("POST /promote", h.Promote)
 	rest.HandleFunc("POST /backfill-embeddings", h.BackfillEmbeddings)
 	rest.HandleFunc("GET /pass-rate", h.PassRate)
-	mux.Handle("/", auth(rest))
+	mux.Handle("/", labelRESTPattern(rest, auth(rest)))
+}
+
+// labelRESTPattern sets the request's Pattern to the REST route it addresses
+// before auth runs, so the metrics middleware (which reads Pattern from the
+// same *http.Request) labels a refused request by its route rather than by
+// the "/" mount (hyperguild#155). A path no route matches keeps "/", so the
+// label set stays bounded by the registered routes.
+func labelRESTPattern(rest *http.ServeMux, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if _, pattern := rest.Handler(r); pattern != "" {
+			r.Pattern = pattern
+		}
+		next.ServeHTTP(w, r)
+	})
 }