fix: propagate api-gateway --timeout flag to per-service dispatchers

The api-gateway accepts a --timeout flag (default 600) but the value is
silently dropped before reaching per-service dispatchers. The flag is
correctly wired to EndpointManager but DispatcherManager constructs every
dispatcher (graph-rag, document-rag, text-completion, embeddings, etc.)
with a hardcoded timeout=120.

Changes:
- Add timeout parameter to DispatcherManager.__init__ (default 120 for
  backward compatibility)
- Replace two hardcoded timeout=120 with self.timeout in
  invoke_global_service() and invoke_flow_service()
- Pass timeout=self.timeout from Api to DispatcherManager in service.py

Fixes: #894

trustgraph-flow/trustgraph/gateway/dispatch/manager.py

@@ -135,13 +135,19 @@ class DispatcherWrapper:
 class DispatcherManager:
 
     def __init__(self, backend, config_receiver, auth,
-                 prefix="api-gateway", queue_overrides=None):
+                 prefix="api-gateway", queue_overrides=None,
+                 timeout=120):
         """
         ``auth`` is required.  It flows into the Mux for first-frame
         WebSocket authentication and into downstream dispatcher
         construction.  There is no permissive default — constructing
         a DispatcherManager without an authenticator would be a
         silent downgrade to no-auth on the socket path.
+
+        ``timeout`` is the API request timeout in seconds for
+        per-service dispatchers.  Must be propagated from the
+        gateway ``--timeout`` flag; defaults to 120 for backward
+        compatibility with callers that do not pass the argument.
         """
         if auth is None:
             raise ValueError(
@@ -159,6 +165,9 @@ class DispatcherManager:
         # identity out-of-band.
         self.auth = auth
 
+        # Timeout for per-service dispatcher requests.
+        self.timeout = timeout
+
         # Store queue overrides for global services
         # Format: {"config": {"request": "...", "response": "..."}, ...}
         self.queue_overrides = queue_overrides or {}
@@ -291,7 +300,7 @@ class DispatcherManager:
 
                     dispatcher = global_dispatchers[kind](
                         backend = self.backend,
-                        timeout = 120,
+                        timeout = self.timeout,
                         consumer = consumer_name,
                         subscriber = consumer_name,
                         request_queue = request_queue,
@@ -448,7 +457,7 @@ class DispatcherManager:
                             backend = self.backend,
                             request_queue = qconfig["request"],
                             response_queue = qconfig["response"],
-                            timeout = 120,
+                            timeout = self.timeout,
                             consumer = f"{self.prefix}-{workspace}-{flow}-{kind}-request",
                             subscriber = f"{self.prefix}-{workspace}-{flow}-{kind}-request",
                         )

trustgraph-flow/trustgraph/gateway/service.py

@@ -119,6 +119,7 @@ class Api:
             prefix = "gateway",
             queue_overrides = queue_overrides,
             auth = self.auth,
+            timeout = self.timeout,
         )
 
         self.endpoint_manager = EndpointManager(