Copilot correctly flagged two concurrency windows:
- memoryMonitor could re-enter while awaiting the lazy @hermes/ink import or
heap dump, producing duplicate imports/dumps under sustained pressure.
- _start_agent_build used a check-then-set guard without synchronization, so
concurrent agent-backed RPCs could start duplicate agent builders.
Fix both with single-flight guards: cache the dynamic import promise and track
per-level dump in-flight state in memoryMonitor, and protect the TUI agent build
flag with a per-session lock.
Tests:
- python -m py_compile tui_gateway/server.py
- cd ui-tui && npm run type-check && npm run build
- cd ui-tui && npm test -- --run src/__tests__/useSessionLifecycle.test.ts src/__tests__/useConfigSync.test.ts
- scripts/run_tests.sh tests/tui_gateway/test_protocol.py::test_sess_found tests/tools/test_code_execution_modes.py tests/tools/test_code_execution.py
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