## What changed
- Subscribe each gRPC code-mode session to nested tool calls and forward tool and notification callbacks to its delegate.
- Complete tool calls through the host while bounding oversized results and errors.
- Track callback ownership and cancellation so completed cells drain notifications, terminated cells cancel them, and shutdown revokes outstanding work.
- Validate callback identifiers, cell ownership, enabled tools, and pending callback limits without serializing independent callbacks or sessions.
## Testing
- Add integration and state tests for callback forwarding, completion ordering, cancellation, malformed callbacks, delegate panics, oversized results, and concurrent work.
GitOrigin-RevId: 005afbb90eea0eb77d746b930a1a96ca6dfcd4e7
## What changed
- Move the host process harness and common session delegates into shared test
support modules.
- Allow the host harness to start either WebSocket or gRPC listeners and
validate the endpoint scheme they publish.
- Update the stdio and WebSocket integration tests to use the shared fixtures.
GitOrigin-RevId: a0408be7c88e4eb9ad1832b6d2698781de77168a
