feat: block direct MCP imports and unsanctioned keychain access (Closes #558)

Require a sanctioned MCP daemon (or pytest) before get_auth_header and
keychain credential fill so raw shell imports cannot bypass preflight gates.

gitea_auth.py

@@ -104,6 +104,10 @@ def get_credentials(host):
 
     # 3. Optional fallback to macOS Keychain via git credential fill
     if not user and not password and os.environ.get("GITEA_USE_KEYCHAIN") == "1":
+        # #558: block raw keychain dumps outside the sanctioned MCP daemon.
+        import mcp_daemon_guard
+
+        mcp_daemon_guard.assert_keychain_access_allowed()
         cmd_parts = ["git", "creden" + "tial", "fi" + "ll"]
         try:
             p = subprocess.Popen(
@@ -116,6 +120,8 @@ def get_credentials(host):
                     user = line.split("=", 1)[1]
                 elif line.startswith("password="):
                     password = line.split("=", 1)[1]
+        except mcp_daemon_guard.UnsanctionedRuntimeError:
+            raise
         except Exception:
             pass
 
@@ -124,6 +130,11 @@ def get_credentials(host):
 
 def get_auth_header(host):
     """Return an ``Authorization`` header value for *host*."""
+    # #558: resolving credentials for API mutation must not happen via ad-hoc
+    # direct imports that bypass the MCP daemon preflight wall.
+    import mcp_daemon_guard
+
+    mcp_daemon_guard.assert_sanctioned_mutation_runtime("get_auth_header")
     host_key = host.lower().strip()
 
     # 1. Try Token-based auth from dynamic configs