Keep the MCP stdio server alive after malformed request frames

docs/design/host-adapters.md

@@ -49,3 +49,5 @@ ordinary external Stores are read-only to the agent shell. Controlled runs isola
 state while reusing only an explicit auth file. Hook and MCP writes require a live compatibility
 preflight. Results are not attributable until native memory is isolated and the tested build
 passes that preflight.
+
+The stdio adapter returns JSON-RPC parse or invalid-request errors for malformed frames and continues reading subsequent requests. An explicit null request ID receives a response, while requests without an ID retain notification behavior. Error codes and envelope rules follow https://www.jsonrpc.org/specification.

packages/mcp/src/agent_memory/mcp/server.py

@@ -24,10 +24,17 @@
 ERROR_INVALID_PARAMS = -32602
 
 
-def handle(store: Store, request: dict[str, object]) -> dict[str, object] | None:
-    method = str(request.get("method") or "")
+def handle(store: Store, request: object) -> dict[str, object] | None:
+    if (
+        not isinstance(request, dict)
+        or request.get("jsonrpc") != JSONRPC
+        or not isinstance(request.get("method"), str)
+        or isinstance(request.get("id"), (dict, list, bool))
+    ):
+        return _error(None, -32600, {"message": "Invalid Request"})
+    method = request["method"]
     request_id = request.get("id")
-    if request_id is None:
+    if "id" not in request:
         return None
     try:
         result = _route(store, method, request.get("params") or {})
@@ -42,7 +49,14 @@ def serve(store: Store, stream_in: TextIO, stream_out: TextIO) -> None:
     for line in stream_in:
         if not line.strip():
             continue
-        response = handle(store, json.loads(line))
+        try:
+            request = json.loads(line)
+        except json.JSONDecodeError:
+            response: dict[str, object] | None = _error(
+                None, -32700, {"message": "Parse error"}
+            )
+        else:
+            response = handle(store, request)
         if response is None:
             continue
         stream_out.write(json.dumps(response) + "\n")

tests/unit/test_regression_mcp_invalid_framing.py

@@ -0,0 +1,33 @@
+import io
+import json
+
+import pytest
+from agent_memory.mcp import server
+
+
+@pytest.mark.parametrize(
+    "malformed,code",
+    [
+        ("{", -32700),
+        ("null", -32600),
+        ('"text"', -32600),
+        ("7", -32600),
+        ('{"jsonrpc":"2.0","method":7,"id":1}', -32600),
+    ],
+)
+def test_bad_frame_reports_protocol_error_and_next_request_still_runs(store, malformed, code):
+    following = {"jsonrpc": "2.0", "id": 8, "method": "tools/list"}
+    output = io.StringIO()
+    server.serve(store, io.StringIO(malformed + "\n" + json.dumps(following) + "\n"), output)
+    responses = [json.loads(line) for line in output.getvalue().splitlines()]
+    assert responses[0]["error"]["code"] == code
+    assert responses[0]["id"] is None
+    assert responses[1]["id"] == 8
+    assert responses[1]["result"]["tools"]
+
+
+def test_explicit_null_id_receives_a_response(store):
+    response = server.handle(store, {"jsonrpc": "2.0", "id": None, "method": "tools/list"})
+    assert response is not None
+    assert response["id"] is None
+    assert response["result"]["tools"]