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fix: harden MCP write tool errors

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This commit is contained in:
Bernd Worsch
2026-06-07 19:30:58 +02:00
parent 8191a3e85d
commit 2cad5da0ab
4 changed files with 424 additions and 21 deletions
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36
mcp_server/TOOLS.md
View File

@@ -20,6 +20,42 @@ Do not use them as a substitute for formal work definition inside the domain rep
---
## MCP/REST Parity and Failure Handling
The MCP server is a thin stateless HTTP client over the FastAPI service. On
successful writes, MCP tools return the same JSON object shape as the REST
endpoint they wrap:
| MCP tool | REST endpoint |
|---|---|
| `create_workstream(...)` | `POST /workstreams/` |
| `create_task(...)` | `POST /tasks/` |
| `update_task_status(...)` | `PATCH /tasks/{task_id}` |
| `record_decision(...)` | `POST /decisions/` |
| `add_progress_event(...)` | `POST /progress/` |
For write tools that emit automatic progress events, the progress event is only
sent after the primary REST write returns a valid object. If the API is
unreachable, returns an HTTP error, or returns a malformed object, the MCP tool
returns a JSON error payload instead:
```json
{
"error": "API 404: ...",
"tool": "update_task_status",
"response": {"error": "API 404: ..."}
}
```
That error is intentional and actionable: do not treat it as success. Fall back
to the corresponding REST `curl` call from the repo instructions, then record a
normal progress event once the REST write succeeds. If the primary write
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.
---
## Query Tools (read-only, use freely)
| Tool | Key Args | When to use |

124
mcp_server/server.py
View File

@@ -92,6 +92,54 @@ def _delete(path: str) -> None:
return {"error": f"Request failed: {e}"}
def _mcp_error(tool_name: str, message: str, response: Any | None = None) -> dict[str, Any]:
payload: dict[str, Any] = {"error": message, "tool": tool_name}
if response is not None:
payload["response"] = response
return payload
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 isinstance(response.get("error"), str):
return _mcp_error(tool_name, response["error"], response)
if not isinstance(response, dict):
return _mcp_error(tool_name, "API returned a non-object response", response)
missing = [field for field in required_fields if response.get(field) is None]
if missing:
return _mcp_error(
tool_name,
f"API response missing required field(s): {', '.join(missing)}",
response,
)
return None
def _emit_progress_event(
tool_name: str,
write_result: dict[str, Any],
body: dict[str, Any],
) -> dict[str, Any] | None:
progress = _post("/progress", body)
error = _response_error(f"{tool_name}.progress_event", progress, ("id",))
if error:
return _mcp_error(
tool_name,
"Primary write succeeded, but automatic progress_event failed",
{"write_result": write_result, "progress_error": error},
)
return None
def _json_result(result: Any) -> str:
return json.dumps(result, indent=2)
# ---------------------------------------------------------------------------
# Resources
# ---------------------------------------------------------------------------
@@ -449,7 +497,10 @@ def create_workstream(
"planning_priority": planning_priority,
"planning_order": planning_order,
})
_post("/progress", {
if error := _response_error("create_workstream", ws, ("id",)):
return _json_result(error)
progress_error = _emit_progress_event("create_workstream", ws, {
"topic_id": topic_id,
"workstream_id": ws["id"],
"event_type": "workstream_created",
@@ -457,7 +508,9 @@ def create_workstream(
"author": "custodian",
"detail": {"owner": owner, "slug": slug},
})
return json.dumps(ws, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(ws)
@mcp.tool()
@@ -487,7 +540,10 @@ def create_task(
"assignee": assignee,
"due_date": due_date,
})
_post("/progress", {
if error := _response_error("create_task", task, ("id",)):
return _json_result(error)
progress_error = _emit_progress_event("create_task", task, {
"workstream_id": workstream_id,
"task_id": task["id"],
"event_type": "task_created",
@@ -495,7 +551,9 @@ def create_task(
"author": "custodian",
"detail": {"priority": priority, "assignee": assignee},
})
return json.dumps(task, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(task)
@mcp.tool()
@@ -558,7 +616,10 @@ def update_task_status(
body["token_note"] = note
task = _patch(f"/tasks/{task_id}", body)
_post("/progress", {
if error := _response_error("update_task_status", task, ("id", "title")):
return _json_result(error)
progress_error = _emit_progress_event("update_task_status", task, {
"task_id": task_id,
"workstream_id": task.get("workstream_id"),
"event_type": "task_status_changed",
@@ -566,8 +627,10 @@ def update_task_status(
"author": "custodian",
"detail": {"blocking_reason": blocking_reason},
})
if progress_error:
return _json_result(progress_error)
return json.dumps(task, indent=2)
return _json_result(task)
@mcp.tool()
@@ -585,7 +648,10 @@ def flag_for_human(task_id: str, note: str) -> str:
"needs_human": True,
"intervention_note": note,
})
_post("/progress", {
if error := _response_error("flag_for_human", task, ("id", "title")):
return _json_result(error)
progress_error = _emit_progress_event("flag_for_human", task, {
"task_id": task_id,
"workstream_id": task.get("workstream_id"),
"event_type": "task_flagged_human",
@@ -593,7 +659,9 @@ def flag_for_human(task_id: str, note: str) -> str:
"author": "custodian",
"detail": {"intervention_note": note},
})
return json.dumps(task, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(task)
@mcp.tool()
@@ -609,14 +677,19 @@ def clear_human_flag(task_id: str) -> str:
task = _patch(f"/tasks/{task_id}", {
"needs_human": False,
})
_post("/progress", {
if error := _response_error("clear_human_flag", task, ("id", "title")):
return _json_result(error)
progress_error = _emit_progress_event("clear_human_flag", task, {
"task_id": task_id,
"workstream_id": task.get("workstream_id"),
"event_type": "task_flag_cleared",
"summary": f"Human-intervention flag cleared: {task['title']}",
"author": "custodian",
})
return json.dumps(task, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(task)
@mcp.tool()
@@ -671,7 +744,10 @@ def record_decision(
"decided_by": decided_by,
"deadline": deadline,
})
_post("/progress", {
if error := _response_error("record_decision", decision, ("id",)):
return _json_result(error)
progress_error = _emit_progress_event("record_decision", decision, {
"topic_id": topic_id,
"workstream_id": workstream_id,
"decision_id": decision["id"],
@@ -680,7 +756,9 @@ def record_decision(
"author": "custodian",
"detail": {"status": decision.get("status"), "escalation_note": decision.get("escalation_note")},
})
return json.dumps(decision, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(decision)
@mcp.tool()
@@ -703,7 +781,10 @@ def resolve_decision(
"decided_by": decided_by,
"decided_at": datetime.now(tz=timezone.utc).isoformat(),
})
_post("/progress", {
if error := _response_error("resolve_decision", decision, ("id", "title")):
return _json_result(error)
progress_error = _emit_progress_event("resolve_decision", decision, {
"topic_id": decision.get("topic_id"),
"workstream_id": decision.get("workstream_id"),
"decision_id": decision_id,
@@ -712,7 +793,9 @@ def resolve_decision(
"author": "custodian",
"detail": {"rationale": rationale},
})
return json.dumps(decision, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(decision)
@mcp.tool()
@@ -748,7 +831,9 @@ def add_progress_event(
"author": "custodian",
"detail": detail,
})
return json.dumps(event, indent=2)
if error := _response_error("add_progress_event", event, ("id",)):
return _json_result(error)
return _json_result(event)
@mcp.tool()
@@ -760,14 +845,19 @@ def update_workstream_status(workstream_id: str, status: str) -> str:
status: proposed | ready | active | blocked | backlog | finished | archived
"""
ws = _patch(f"/workstreams/{workstream_id}", {"status": status})
_post("/progress", {
if error := _response_error("update_workstream_status", ws, ("id", "title")):
return _json_result(error)
progress_error = _emit_progress_event("update_workstream_status", ws, {
"workstream_id": workstream_id,
"topic_id": ws.get("topic_id"),
"event_type": "workstream_status_changed",
"summary": f"Workstream status → {status}: {ws['title']}",
"author": "custodian",
})
return json.dumps(ws, indent=2)
if progress_error:
return _json_result(progress_error)
return _json_result(ws)
@mcp.tool()

254
tests/test_mcp_write_tools.py Normal file
View File

@@ -0,0 +1,254 @@
"""
Regression tests for State Hub MCP write tools.
These call the registered FastMCP tools in-process and monkeypatch only the
thin HTTP helpers. That exercises FastMCP argument validation and the MCP
wrapper logic without depending on a running State Hub API.
"""
from __future__ import annotations
import json
from typing import Any
import mcp_server.server as server
async def _call_tool(name: str, arguments: dict[str, Any]) -> dict[str, Any]:
result = await server.mcp.call_tool(name, arguments)
return json.loads(result.content[0].text)
class TestMCPWriteTools:
async def test_create_workstream_returns_rest_shape_and_emits_progress(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
if path == "/workstreams":
return {
"id": "ws-1",
"topic_id": body["topic_id"],
"title": body["title"],
"slug": body["slug"],
"status": body["status"],
}
if path == "/progress":
return {"id": "event-1", **body}
raise AssertionError(f"unexpected POST {path}")
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"create_workstream",
{"topic_id": "topic-1", "title": "MCP Reliable Write"},
)
assert body == {
"id": "ws-1",
"topic_id": "topic-1",
"title": "MCP Reliable Write",
"slug": "mcp-reliable-write",
"status": "active",
}
assert [path for path, _ in calls] == ["/workstreams", "/progress"]
assert calls[1][1]["workstream_id"] == "ws-1"
assert calls[1][1]["event_type"] == "workstream_created"
async def test_create_task_returns_rest_shape_and_emits_progress(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
if path == "/tasks":
return {
"id": "task-1",
"workstream_id": body["workstream_id"],
"title": body["title"],
"priority": body["priority"],
"status": "todo",
}
if path == "/progress":
return {"id": "event-1", **body}
raise AssertionError(f"unexpected POST {path}")
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"create_task",
{"workstream_id": "ws-1", "title": "MCP task", "priority": "high"},
)
assert body == {
"id": "task-1",
"workstream_id": "ws-1",
"title": "MCP task",
"priority": "high",
"status": "todo",
}
assert [path for path, _ in calls] == ["/tasks", "/progress"]
assert calls[1][1]["task_id"] == "task-1"
assert calls[1][1]["event_type"] == "task_created"
async def test_update_task_status_api_error_is_clear_and_skips_progress(self, monkeypatch):
post_calls: list[tuple[str, dict[str, Any]]] = []
def fake_patch(path: str, body: dict[str, Any]) -> dict[str, Any]:
assert path == "/tasks/task-1"
assert body["status"] == "done"
return {"error": "API 404: task not found"}
monkeypatch.setattr(server, "_patch", fake_patch)
monkeypatch.setattr(server, "_post", lambda path, body: post_calls.append((path, body)))
body = await _call_tool(
"update_task_status",
{"task_id": "task-1", "status": "done"},
)
assert body["tool"] == "update_task_status"
assert body["error"] == "API 404: task not found"
assert post_calls == []
async def test_update_task_status_returns_rest_shape_and_emits_progress(self, monkeypatch):
post_calls: list[tuple[str, dict[str, Any]]] = []
def fake_patch(path: str, body: dict[str, Any]) -> dict[str, Any]:
assert path == "/tasks/task-1"
assert body["status"] == "done"
return {
"id": "task-1",
"workstream_id": "ws-1",
"title": "Finish MCP reliability",
"status": "done",
}
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
post_calls.append((path, body))
return {"id": "event-1", **body}
monkeypatch.setattr(server, "_patch", fake_patch)
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"update_task_status",
{"task_id": "task-1", "status": "done"},
)
assert body == {
"id": "task-1",
"workstream_id": "ws-1",
"title": "Finish MCP reliability",
"status": "done",
}
assert [path for path, _ in post_calls] == ["/progress"]
assert post_calls[0][1]["task_id"] == "task-1"
assert post_calls[0][1]["event_type"] == "task_status_changed"
async def test_add_progress_event_accepts_json_string_detail(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
return {"id": "event-1", **body}
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"add_progress_event",
{
"summary": "MCP progress",
"event_type": "note",
"workstream_id": "ws-1",
"detail": '{"files_changed": 3}',
},
)
assert body["id"] == "event-1"
assert body["detail"] == {"files_changed": 3}
assert calls == [
(
"/progress",
{
"topic_id": None,
"workstream_id": "ws-1",
"task_id": None,
"event_type": "note",
"summary": "MCP progress",
"author": "custodian",
"detail": {"files_changed": 3},
},
)
]
async def test_record_decision_returns_rest_shape_and_emits_progress(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
if path == "/decisions":
return {
"id": "decision-1",
"title": body["title"],
"decision_type": body["decision_type"],
"topic_id": body["topic_id"],
"workstream_id": body["workstream_id"],
"status": "open",
"escalation_note": None,
}
if path == "/progress":
return {"id": "event-1", **body}
raise AssertionError(f"unexpected POST {path}")
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"record_decision",
{
"title": "Keep MCP stateless",
"decision_type": "made",
"topic_id": "topic-1",
"workstream_id": "ws-1",
},
)
assert body["id"] == "decision-1"
assert body["title"] == "Keep MCP stateless"
assert [path for path, _ in calls] == ["/decisions", "/progress"]
assert calls[1][1]["decision_id"] == "decision-1"
assert calls[1][1]["event_type"] == "decision_recorded"
async def test_create_workstream_api_error_skips_progress(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
return {"error": "API 422: invalid topic"}
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"create_workstream",
{"topic_id": "bad-topic", "title": "No progress on failure"},
)
assert body["tool"] == "create_workstream"
assert body["error"] == "API 422: invalid topic"
assert [path for path, _ in calls] == ["/workstreams"]
async def test_record_decision_missing_id_is_clear_and_skips_progress(self, monkeypatch):
calls: list[tuple[str, dict[str, Any]]] = []
def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
calls.append((path, body))
return {"title": body["title"], "status": "open"}
monkeypatch.setattr(server, "_post", fake_post)
body = await _call_tool(
"record_decision",
{"title": "Malformed API response", "topic_id": "topic-1"},
)
assert body["tool"] == "record_decision"
assert body["error"] == "API response missing required field(s): id"
assert [path for path, _ in calls] == ["/decisions"]

31
workplans/STATE-WP-0059-mcp-write-layer-reliability.md
View File

@@ -4,7 +4,7 @@ type: workplan
title: "State Hub MCP write-layer reliability"
domain: custodian
repo: state-hub
status: ready
status: finished
owner: codex
topic_slug: custodian
created: "2026-06-07"
@@ -67,7 +67,7 @@ record status/progress, leaving file↔hub drift unreconciled.
```task
id: STATE-WP-0059-T01
status: todo
status: done
priority: high
state_hub_task_id: "7fc04b00-2493-4310-ae76-101660621da6"
```
@@ -90,7 +90,7 @@ tool wrapper, not only the FastAPI endpoint, and records:
```task
id: STATE-WP-0059-T02
status: todo
status: done
priority: high
state_hub_task_id: "2636e1d5-142e-463f-875e-4dc1edf12853"
```
@@ -117,7 +117,7 @@ Implementation notes:
```task
id: STATE-WP-0059-T03
status: todo
status: done
priority: medium
state_hub_task_id: "af137d6b-07ca-4110-abb0-45a96b84b7a3"
```
@@ -143,3 +143,26 @@ After workplan updates, run from `~/state-hub`:
```bash
make fix-consistency REPO=state-hub
```
## Verification Notes
Completed 2026-06-07:
- Added shared MCP response/error helpers in `mcp_server/server.py` so API error
payloads and malformed REST responses return clear MCP-visible errors instead
of triggering response-field KeyErrors or false success.
- Kept successful MCP write responses in the same JSON shape as their REST
equivalents, while preserving automatic progress events only after successful
primary writes.
- Added `tests/test_mcp_write_tools.py`, which invokes the registered FastMCP
tools in-process and covers success/error behavior for `create_workstream`,
`create_task`, `update_task_status`, `add_progress_event`, and
`record_decision`.
- Documented MCP/REST write parity and fallback expectations in
`mcp_server/TOOLS.md`.
Verification:
- `.venv/bin/python -m pytest tests/test_mcp_write_tools.py -q` -> 8 passed
- `.venv/bin/python -m pytest tests/test_mcp_write_tools.py tests/test_mcp_smoke.py -q` -> 21 passed
- `git diff --check` -> clean