The #54878 self-heal (SessionStore.get_or_create_session) drops a routing
key pointing at a session already ended in state.db and recovers/recreates
a fresh session_id under the same session_key. The #54947 fix (agent-cache
cache-hit guard in gateway/run.py) treats a cached agent whose snapshot
session_id differs from the current session_id, under the same
session_key, as an intentional /resume-/branch-style switch between two
live sibling conversations, and reuses it unchanged to protect the prompt
cache.
These two fixes compose incorrectly: when the #54878 self-heal just fired,
the cached agent's session_id is not a live sibling — it's the dead session
just routed away from. #54947's "different session_id -> reuse freely" rule
reuses it anyway. The stale agent runs the turn, and the post-run "session
split" sync (agent.session_id != session_id) then writes the routing key
straight back onto the dead session_id, undoing the self-heal. This repeats
on every subsequent message until an interrupt (e.g. /stop) happens to race
in before that post-run sync, silently discarding conversation context.
Reproduced live on the engineering gateway (2026-07-12, routing key
agent:main:telegram:dm:170829464:544520): 5 consecutive self-heal log lines
over ~40 minutes, each followed by the dead session_id being reused and
re-synced back, until an interrupted /stop finally let a fresh session
stick — at which point all prior context was gone.
No open upstream issue tracks this specific interaction as of 2026-07-12
(checked #54878, #54947, #59580, #59597, #61220 — all cover adjacent but
distinct edges of the self-heal / agent-cache system).
Fix: before applying #54947's reuse-on-mismatch rule, check (outside the
cache lock, via SessionStore._is_session_ended_in_db) whether the cached
snapshot's session_id is itself ended in state.db. If so, treat it as a
stale self-heal artifact and evict/rebuild fresh -- same as a genuine
cross-process write -- instead of reusing it. Re-validates the peeked
verdict against the tuple actually held under the lock so a race can't
apply a stale verdict to a different (possibly live) cache entry.
Tests: tests/gateway/test_stale_self_heal_agent_cache_eviction.py (5 new
cases: dead-session eviction, live-sibling reuse preserved [#54947 intact],
cross-process invalidation preserved [#45966 intact], same-session_id dead
edge case, lock-race re-validation). Full tests/gateway/ suite: 14 failed,
9040 passed, 11 skipped -- all 14 failures verified pre-existing on
unpatched main (confirmed via git stash + re-run), unrelated to this
change.
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