fix(mcp): auto-proxy to daemon when database is locked

When a daemon process holds the database lock, serve now auto-detects
it via daemon.edn and proxies tool calls to it instead of failing.
Also resolves noum binary path via PATH for Homebrew installs, and
surfaces actionable error messages instead of generic "unexpected
internal error" on tool failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: leifericf

launcher/src/noum/setup.clj

@@ -22,6 +22,7 @@
 
 (defn- noum-bin-path []
   (or (System/getenv "NOUM_BIN")
+      (some-> (fs/which "noum") str)
       (str (fs/path (fs/home) ".local" "bin" "noum"))))
 
 (defn- merge-mcp-config [existing]

src/noumenon/mcp.clj

@@ -22,7 +22,8 @@
             [noumenon.sync :as sync]
             [noumenon.synthesize :as synthesize]
             [noumenon.util :as util :refer [log!]])
-  (:import [java.io BufferedReader PrintWriter]))
+  (:import [java.io BufferedReader PrintWriter]
+           [java.lang ProcessHandle]))
 
 ;; --- Helpers ---
 
@@ -1031,12 +1032,21 @@
                              (assoc defaults :progress-fn progress-fn)
                              defaults))
         (catch clojure.lang.ExceptionInfo e
-          (log! "tool/error" tool-name (.getMessage e))
-          (tool-error (or (:user-message (ex-data e))
-                          (str "Internal error: " (.getMessage e)))))
+          (let [msg (.getMessage e)
+                user-msg (:user-message (ex-data e))]
+            (log! "tool/error" tool-name msg)
+            (tool-error (or user-msg
+                            (str "Internal error: " msg)))))
         (catch Exception e
-          (log! "tool/error" tool-name (.getMessage e))
-          (tool-error "An unexpected internal error occurred.")))
+          (let [msg (.getMessage e)]
+            (log! "tool/error" tool-name msg)
+            (tool-error
+             (if (and msg (str/includes? msg ".lock"))
+               (str "FATAL: Database locked by another process (likely a running daemon). "
+                    "DO NOT RETRY — all Noumenon tool calls will fail until the lock is released. "
+                    "Tell the user to kill the daemon: ps aux | grep 'noumenon.*daemon' | grep -v grep | awk '{print $2}' | xargs kill")
+               (str "Internal error in " tool-name ": " msg
+                    ". DO NOT RETRY — report this error to the user."))))))
       (tool-error (str "Unknown tool: " tool-name)))))
 
 ;; --- Main loop ---
@@ -1080,6 +1090,19 @@
         (when (and active (not= active "local"))
           (get-in config [:connections active]))))))
 
+(defn- detect-local-daemon
+  "Check ~/.noumenon/daemon.edn for a running local daemon.
+   Returns a proxy connection map if the daemon PID is alive, nil otherwise."
+  []
+  (let [daemon-file (io/file (System/getProperty "user.home") ".noumenon" "daemon.edn")]
+    (when (.exists daemon-file)
+      (try
+        (let [{:keys [port pid]} (edn/read-string {:readers {}} (slurp daemon-file))
+              handle (.orElse (ProcessHandle/of pid) nil)]
+          (when (and handle (.isAlive handle) port)
+            {:host (str "http://127.0.0.1:" port)}))
+        (catch Exception _ nil)))))
+
 (defn- repo-path->db-name
   "Translate a local repo_path to a database name for remote queries.
    Tries: git remote origin URL -> org-repo, else basename."
@@ -1163,7 +1186,8 @@
                       arguments)]
       (try
         (let [;; Pass auth header via stdin to avoid token in process list
-              curl-config (str "header = \"Authorization: Bearer " token "\"\n"
+              curl-config (str (when token
+                                 (str "header = \"Authorization: Bearer " token "\"\n"))
                                "header = \"Content-Type: application/json\"\n")
               ;; For GET, append non-empty args as query params
               get-url (if (and (= method :get) (seq args))
@@ -1211,7 +1235,7 @@
   (log! "noumenon MCP server starting")
   (let [reader      (BufferedReader. (io/reader System/in))
         writer      (PrintWriter. System/out true)
-        remote-conn (load-connection-config)
+        remote-conn (or (load-connection-config) (detect-local-daemon))
         defaults    (cond-> (select-keys opts [:db-dir :provider :model])
                       (:no-auto-update opts) (assoc :auto-update false))
         dispatch    (fn [id method params]
@@ -1225,7 +1249,8 @@
                         "resources/list"          (format-response id {:resources []})
                         (format-error id -32601 (str "Method not found: " method))))]
     (when remote-conn
-      (log! (str "MCP proxy mode: forwarding to " (:host remote-conn))))
+      (log! (str "MCP proxy mode: forwarding to " (:host remote-conn)
+                 (when-not (load-connection-config) " (auto-detected local daemon)"))))
     (log! "noumenon MCP server ready")
     (loop []
       (when-let [line (try