Follow-up to the cherry-picked #31856 fix. The contributor's guard defers
idle-TTL eviction until the session store reports the session expired, so the
expiry watcher can tear the agent down and fire MemoryProvider.on_session_end()
with the live transcript. Two gaps remained:
1. Memory-leak regression for mode='none' sessions. _is_session_expired()
returns False forever for the 'none' reset policy, so the naive guard would
never idle-evict those agents — reopening the unbounded-cache leak the idle
sweep (#11565) exists to relieve. Added SessionStore.is_session_finalizable()
(a public predicate: will the expiry watcher EVER finalize this session?) and
gate the deferral on it. mode='none' agents fall through to soft eviction as
before.
2. on_session_end still dropped on the LRU-cap path. Both cache-pressure paths
(_enforce_agent_cache_cap and _sweep_idle_cached_agents) soft-evict via
_release_evicted_agent_soft, which by design does NOT fire on_session_end.
If cache pressure evicts a finalizable-but-not-yet-expired agent before it
expires, the watcher later finds no cached agent and the hook is skipped.
Added _commit_memory_before_soft_evict(): at LRU eviction, if the session is
finalizable and not yet expired, commit end-of-session extraction via the
live agent's own (fully-scoped) memory manager using commit_memory_session()
— extraction WITHOUT provider teardown, so the eviction stays soft and a
resumed turn keeps working. Skipped for mode='none' (no missed boundary to
compensate) and expired sessions (the watcher tears those down directly).
This closes#11205 for ALL eviction paths and reset policies, not just the
idle-sweep + finite-policy case, while preserving the soft-eviction
resumability contract (never calls close() on a live session).
Tests: 5 new cases in test_agent_cache.py (mode='none' still reaped, LRU-cap
commits for finalizable / skips for none, real is_session_finalizable
predicate); all mutation-checked. Contributor's original 2 tests updated to
assert the finalizable path explicitly.
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