fix(contract-drift): MCP read-only scope, shared-note writes, event TZ

Drift-audit Group 5 (high-severity contract drift):

- MCP read-only keys could call every write tool: the Bearer resolver
  discarded api_key.scope and dispatch had no gate. Add resolve_bearer()
  (returns user_id + scope) and a scope gate in the /mcp ASGI wrapper that
  buffers the JSON-RPC body and rejects tools/call for any tool outside a
  read all-list when scope=='read' (default-deny for unknown/new tools).
- Shared project notes/tasks panel was empty for non-owners: get_project_notes_route
  now queries notes/milestones with the project OWNER's uid (mirrors the
  already-fixed milestones route).
- Shared editors couldn't save/delete shared NOTES (tasks worked): the three
  notes write routes now resolve via get_note_for_user, gate on can_write_note,
  and write as the owner — matching the tasks routes.
- Event timezone drift: naive datetimes from the MCP date+time split are now
  localized to the user's tz at a single canonical service point (create_event
  /update_event), so MCP- and UI-created events agree. tz-aware inputs
  (REST/CalDAV) pass through untouched.
- create_note validates status/priority (TaskStatus/TaskPriority), closing the
  MCP create_task path that let out-of-enum values persist (no DB CHECK).

Tests cover resolve_bearer scope + the write-tool classifier.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/fabledassistant/mcp/auth.py

@@ -17,3 +17,21 @@ async def resolve_bearer_to_user_id(auth_header: str | None) -> int | None:
         return None
     api_key = await lookup_key(raw_token)
     return api_key.user_id if api_key else None
+
+
+async def resolve_bearer(auth_header: str | None) -> tuple[int, str] | None:
+    """Resolve a Bearer token to (user_id, scope).
+
+    scope is 'read' or 'write'. Returns None for a missing/malformed/invalid
+    token. The MCP dispatch layer uses scope to deny write-class tool calls
+    from read-only keys — the same read/write boundary the REST API enforces.
+    """
+    if not auth_header or not auth_header.startswith("Bearer "):
+        return None
+    raw_token = auth_header[len("Bearer "):].strip()
+    if not raw_token:
+        return None
+    api_key = await lookup_key(raw_token)
+    if api_key is None:
+        return None
+    return api_key.user_id, (api_key.scope or "write")

src/fabledassistant/mcp/server.py

@@ -81,6 +81,66 @@ auto-purges after the operator's retention window.
 """
 
 
+# Tools a read-only API key may call. Anything not listed is treated as a
+# write for read keys (default-deny), so a newly-added tool is locked down
+# until explicitly classified here.
+_READ_ONLY_TOOLS = frozenset({
+    "get_event", "get_note", "get_project", "get_rule", "get_rulebook",
+    "get_task", "get_recent", "enter_project",
+    "list_events", "list_lists", "list_milestones", "list_notes",
+    "list_persons", "list_places", "list_projects", "list_rulebooks",
+    "list_rules", "list_tags", "list_tasks", "list_topics", "list_trash",
+    "list_always_on_rules", "search",
+})
+
+
+async def _buffer_request_body(receive):
+    """Drain the ASGI request body and return (body_bytes, replay_receive).
+
+    The MCP sub-app still needs to read the body, so we return a fresh
+    `receive` that replays the buffered bytes.
+    """
+    chunks: list[bytes] = []
+    more = True
+    while more:
+        message = await receive()
+        if message["type"] == "http.request":
+            chunks.append(message.get("body", b""))
+            more = message.get("more_body", False)
+        else:  # http.disconnect
+            more = False
+    body = b"".join(chunks)
+
+    sent = False
+
+    async def replay():
+        nonlocal sent
+        if not sent:
+            sent = True
+            return {"type": "http.request", "body": body, "more_body": False}
+        return {"type": "http.disconnect"}
+
+    return body, replay
+
+
+def _body_calls_write_tool(body: bytes) -> bool:
+    """True if the JSON-RPC body invokes a tool outside the read all-list."""
+    import json
+    try:
+        payload = json.loads(body)
+    except Exception:
+        return False
+    items = payload if isinstance(payload, list) else [payload]
+    for item in items:
+        if not isinstance(item, dict):
+            continue
+        if item.get("method") == "tools/call":
+            name = (item.get("params") or {}).get("name", "")
+            if name and name not in _READ_ONLY_TOOLS:
+                return True
+    return False
+
+
 def build_mcp_server() -> FastMCP:
     """Build the FastMCP instance with all tools registered.
 
@@ -128,7 +188,7 @@ def mount_mcp(app: Quart) -> None:
     inside Quart, we hook the session manager's `run()` async context manager
     into Quart's serving lifecycle (before_serving / after_serving).
     """
-    from fabledassistant.mcp.auth import resolve_bearer_to_user_id
+    from fabledassistant.mcp.auth import resolve_bearer
 
     mcp = build_mcp_server()
     mcp_asgi = mcp.streamable_http_app()
@@ -151,8 +211,8 @@ def mount_mcp(app: Quart) -> None:
             return await mcp_asgi(scope, receive, send)
         # ASGI headers are lowercase bytes per spec; lowercase explicitly to be safe.
         headers = {k.decode().lower(): v.decode() for k, v in scope.get("headers", [])}
-        user_id = await resolve_bearer_to_user_id(headers.get("authorization"))
-        if user_id is None:
+        resolved = await resolve_bearer(headers.get("authorization"))
+        if resolved is None:
             await send({
                 "type": "http.response.start",
                 "status": 401,
@@ -166,6 +226,27 @@ def mount_mcp(app: Quart) -> None:
                 "body": b'{"error":"unauthorized"}',
             })
             return
+        user_id, key_scope = resolved
+
+        # Enforce read-only keys: REST blocks non-GET for scope='read', and the
+        # MCP surface must match or the read-only guarantee is void. A tool call
+        # arrives as a JSON-RPC POST; buffer the body, and if it invokes a tool
+        # outside the read all-list, reject before dispatch. (default-deny: any
+        # unknown/new tool is treated as a write for read keys.)
+        if key_scope == "read" and scope.get("method") == "POST":
+            body, receive = await _buffer_request_body(receive)
+            if _body_calls_write_tool(body):
+                await send({
+                    "type": "http.response.start",
+                    "status": 403,
+                    "headers": [(b"content-type", b"application/json")],
+                })
+                await send({
+                    "type": "http.response.body",
+                    "body": b'{"error":"read-only API key cannot call write tools"}',
+                })
+                return
+
         scope["scribe_user_id"] = user_id
         from fabledassistant.mcp._context import _user_id_ctx
         token = _user_id_ctx.set(user_id)