refactor(mcp): declare _resolved_identity in MCPServerTask's slots and init it

The transport publishes _resolved_identity and server_run resets it, but the attribute was
neither in __slots__ nor set in __init__, so a task that never reached the transport raised
AttributeError on read and the attribute silently lived in the mixins' __dict__. Declare it and
start it at None (not shareable until the transport publishes a digest). The getattr in
registration stays for test fakes that are not MCPServerTask instances.

tools/mcp_tool.py

@@ -317,7 +317,7 @@ class MCPServerTask(MCPServerRunMixin, MCPServerTransportMixin, MCPServerHealthM
         "_recycled_reason", "initialize_result", "_ping_unsupported", "_list_cache_meta",
         "_reconnect_retries", "_session_proven", "_was_parked", "_inflight_tasks", "_reconnecting",
         "_suspect_reason", "_teardown_race", "_permanent_grace_used", "_stdio_child_pids",
-        "_ever_connected", "_sse_fallback", "_park_reason", "_last_park_line")
+        "_ever_connected", "_sse_fallback", "_park_reason", "_last_park_line", "_resolved_identity")
 
     def __init__(self, name: str):
         self.name = name
@@ -358,6 +358,9 @@ class MCPServerTask(MCPServerRunMixin, MCPServerTransportMixin, MCPServerHealthM
         # (revoked credentials, dead endpoint) that must not run the job tool-less forever.
         self._park_reason: Optional[str] = None
         self._last_park_line: Optional[str] = None  # last park WARNING text; identical re-parks log at DEBUG
+        # Digest of the resolved inputs the transport last connected with; a cross-profile adopter
+        # must resolve the same digest in its own scope. None until the transport publishes it.
+        self._resolved_identity: Optional[str] = None
         # In-flight RPC tasks so a deliberate teardown fails them fast; _reconnecting is True
         # during that teardown so _track_inflight_rpc turns the cancel into a retryable error.
         # In-flight RPC bookkeeping (#48069 salvage): user-visible requests registered while running so a