fix(ingestion): close the PR #152 review findings on REST auth

- main.go's wiring was untested (the test built its own copy of the
  router, so dropping auth in main or re-registering POST /query as
  public stayed green). Routing is now one function, buildMux, which
  main calls and the tests call: it constructs the bearer middleware
  itself, registers public handlers only for patterns on a fixed
  allowlist (a public REST pattern would beat the authenticated
  catch-all by specificity), refuses an empty token, and returns an
  http.Handler so nothing can add a route to the result.
- hyperguild CLI: PassRate sent no token and would 401. Every request
  now goes through brainClient.do, which adds it; the test covers
  Query, Write and PassRate and is named for that.
- ResolveIngestPath returns one refusal for every bad path; the raw
  EvalSymlinks error let a caller probe which server files exist and
  leaked the brain directory.
- PROJECT.md (and derived adapters) and the pass-rate runbook state
  that the REST API needs BRAIN_MCP_TOKEN and is tailnet/in-cluster.

Refs #149

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

ingestion/cmd/server/main.go

@@ -503,9 +503,10 @@ func main() {
 		logger.Info("embed sync started", "interval_s", embedSyncInterval)
 	}
 
-	mux := http.NewServeMux()
+	// Public routes only; buildMux mounts the authenticated REST API (#149).
+	public := map[string]http.Handler{}
 	if webhookHandler != nil {
-		mux.Handle("POST /webhooks/brain-sync", webhookHandler)
+		public["POST /webhooks/brain-sync"] = webhookHandler
 	}
 	// Resource-metadata URL is only emitted on 401 when Dex OAuth is
 	// configured. Static-Bearer-only deployments leave this empty so
@@ -513,21 +514,14 @@ func main() {
 	var resourceMetadataURL string
 	if dexURL := os.Getenv("DEX_ISSUER_URL"); dexURL != "" {
 		resourceURL := os.Getenv("MCP_RESOURCE_URL")
-		mux.HandleFunc("GET /.well-known/oauth-protected-resource",
+		public["GET /.well-known/oauth-protected-resource"] = http.HandlerFunc(
 			chassisauth.ProtectedResourceHandler(resourceURL, dexURL))
 		if resourceURL != "" {
 			resourceMetadataURL = strings.TrimRight(resourceURL, "/") + "/.well-known/oauth-protected-resource"
 		}
 	}
 
-	mux.Handle("/mcp", chassisauth.BearerMiddleware(mcpToken, jwtValidator, "brain", resourceMetadataURL, mcpSrv))
-	// The REST API, authenticated as a whole (hyperguild#149). Same credential
-	// as /mcp: callers (brain-ui, brain-ingest-ntfy, the hyperguild CLI) send
-	// BRAIN_MCP_TOKEN. Registered after the public routes on purpose only for
-	// reading order; ServeMux precedence is by pattern specificity.
-	mountREST(mux, h, func(next http.Handler) http.Handler {
-		return chassisauth.BearerMiddleware(mcpToken, jwtValidator, "brain", resourceMetadataURL, next)
-	})
+	public["/mcp"] = chassisauth.BearerMiddleware(mcpToken, jwtValidator, "brain", resourceMetadataURL, mcpSrv)
 
 	// POST /capture (#53/#54): the uniform capture REST door. Needs a ticket
 	// tracker to file action items, so it only mounts when Gitea is
@@ -549,7 +543,7 @@ func main() {
 		sovereign := splitList(os.Getenv("BRAIN_CAPTURE_SOVEREIGN_PRINCIPALS"))
 		resolver := capturehttp.NewOriginResolver(sovereign)
 		captureH := capturehttp.New(captureSvc, jwtValidator, mcpToken, "local-cli", resolver)
-		mux.Handle("POST /capture", captureH)
+		public["POST /capture"] = captureH
 		// Same use-case behind the MCP `capture` tool (#55 relay) so MCP-native
 		// harnesses (claude.ai, Crush, Pi, LLM Council) reach capture through
 		// the existing /mcp OAuth connector. mcpSrv is already wrapped above;
@@ -579,9 +573,9 @@ func main() {
 			logger.Error("OAUTH_CLIENT_ID/SECRET set but MCP_RESOURCE_URL is empty; cannot derive issuer")
 			os.Exit(1)
 		}
-		mux.HandleFunc("GET /.well-known/oauth-authorization-server",
+		public["GET /.well-known/oauth-authorization-server"] = http.HandlerFunc(
 			oauth.MetadataHandler(issuer))
-		mux.HandleFunc("POST /oauth/token", oauth.TokenHandler(oauth.TokenConfig{
+		public["POST /oauth/token"] = http.HandlerFunc(oauth.TokenHandler(oauth.TokenConfig{
 			ClientID:     oauthID,
 			ClientSecret: oauthSecret,
 			AccessToken:  mcpToken,
@@ -600,7 +594,17 @@ func main() {
 	// real request latency. /metrics itself is excluded from its own
 	// observation by registering it on the outer mux (post-wrap).
 	reg := metrics.New()
-	mux.HandleFunc("GET /metrics", reg.Handler())
+	public["GET /metrics"] = http.HandlerFunc(reg.Handler())
+
+	// The whole router, built in one place so the test of buildMux is a test
+	// of production wiring (PR #152 review). The REST API's credential is the
+	// same as /mcp's.
+	mux, err := buildMux(restAuth{token: mcpToken, validator: jwtValidator, realm: "brain",
+		resourceMetadataURL: resourceMetadataURL}, h, public)
+	if err != nil {
+		logger.Error("build router", "err", err)
+		os.Exit(1)
+	}
 	logger.Info("metrics endpoint registered", "path", "/metrics")
 
 	addr := ":" + port