The NeMo Relay native binding's scope.pop/push are synchronous and
unbounded ('returns after the scope is closed successfully'). When the
native pipeline cannot make progress, the session coordinator's turn and
session finalization block forever inside run_conversation: delegated
children finish their turns but never return, and delegation batches die
on the stall watchdog. Proven live 2026-08-10 on the staging fleet — a
falsification probe (plugin disabled, identical config) completed the
same delegation batch that wedged with the plugin active.
Bound every scope lifecycle operation that gates turn/session completion
(session push, turn push, turn pop, logical-LLM pops, session pop,
subscriber flush) by running the native call on a shared
DaemonThreadPoolExecutor and honoring a 10s result timeout. On breach a
TimeoutError propagates into each call site's existing exception
handling — warn, retain the unclosed-prefix diagnostics, continue — so
the worst case is one lost span, never a blocked agent. timeout=None
preserves byte-identical synchronous behavior for all other callers, and
interpreter-shutdown paths fall back to the synchronous call so the
atexit flush still exports.
Observability must never block the product.
The native Relay pipeline binds its Futures to the event loop that
entered run_in_session_async. While a managed tool callback executes,
that loop is blocked until the callback returns — so a nested managed
relay call made from inside the callback (vision_analyze's auxiliary
LLM call on a worker-thread loop) awaits a Future that can never
complete: 'RuntimeError: Future attached to a different loop', or a
deadlock, plus 'Event loop is closed' at shutdown when the orphaned
future completes late. (#77244)
Fix: managed_callback_guard, a ContextVar depth marker set around every
Hermes callback the relay adapters hand to the native pipeline
(relay_tools.execute invoke, relay_llm execute/execute_async invoke,
ManagedLlmStream run_callback). resolve_execution_context returns the
no-relay triple while the marker is set, so nested calls run unmanaged.
The marker propagates through contextvars.copy_context() into the
worker threads tools use for their internal async work.
Top-level turn LLM calls and tool wraps stay fully managed — verified
live: vision_analyze works under active shared metrics while the main
turn still records managed llm.execute events.
Alternative fixes considered and rejected: removing
retain_managed_execution (kills the shared-metrics managed pipeline)
and gating on main-thread identity (managed tool wraps legitimately
run on the run_agent thread, so that gate disables relay everywhere).
Victor Kyriazakos