feat(statehub): add offline write buffer relay

mcp_server/TOOLS.md

@@ -82,6 +82,13 @@ succeeds but its automatic progress event fails, the tool returns an error with
 the successful `write_result` included so the caller can avoid duplicating the
 entity while recording the missing progress event.
 
+When API_BASE points at the optional State Hub edge relay and the central API is
+unreachable, queueable write tools may return a queued receipt instead of the
+normal REST shape. The receipt means the local outbox accepted the write; it is
+not yet a central commit. Automatic progress-event side effects are skipped for
+queued primary writes so replay does not duplicate records. Operators can inspect
+and replay with statehub outbox status and statehub outbox replay.
+
 ---
 
 ## Query Tools (read-only, use freely)

mcp_server/server.py

@@ -120,12 +120,23 @@ def _mcp_error(tool_name: str, message: str, response: Any | None = None) -> dic
     return payload
 
 
+
+def _mcp_queued(tool_name: str, response: dict[str, Any]) -> dict[str, Any]:
+    return {
+        "queued": True,
+        "tool": tool_name,
+        "message": "Write queued by State Hub edge relay; central commit is pending replay.",
+        "receipt": response,
+    }
+
 def _response_error(
     tool_name: str,
     response: Any,
     required_fields: tuple[str, ...] = (),
 ) -> dict[str, Any] | None:
     """Return an MCP-visible error payload for failed or malformed API results."""
+    if isinstance(response, dict) and response.get("queued") is True:
+        return _mcp_queued(tool_name, response)
     if isinstance(response, dict) and isinstance(response.get("error"), str):
         return _mcp_error(tool_name, response["error"], response)
     if not isinstance(response, dict):