A first stalled summary stream keeps today's behaviour: the transcript is left
alone, the stall-class cooldown (floored at the idle window) is armed and the
LLM route retries after it lapses. When the route stalls AGAIN while a
stall-class failure is still on the ladder, the stall retry ladder now ends
with a deterministic rung: the worker is re-run with the summary LLM skipped
(DETERMINISTIC_SUMMARY_ROUTE pin, consumed in _summarize_window) and
compress() commits its static fallback summary through the ordinary
lease/fence/watermark pipeline — the same degrade a failed summary call gets
(abort_on_summary_failure still aborts).
WHY: after "made no progress … continuing without compression" the context
stays oversized, so the next turn after the cooldown re-enters the same silent
stream and burns another full idle window; the reporter saw this every ~2 min
for hours (#112420). A route that has proven unhealthy twice must degrade once
instead of looping. The prune-on-stall hunk from #112504 was declined because
it committed outside the lease/fence; this rung reuses the same-turn fallback
worker (bypass_cooldown) and the commit path the fallback_chain retry already
uses, so no new commit surface is introduced.
Also: a pinned fallback_chain route whose summary call FAILS still commits the
static fallback summary (default abort_on_summary_failure=false); the host log
said "recovered on fallback_chain[0]" for that. It now logs "committed a
deterministic fallback summary on …" at WARNING (#112387 review caveat), keyed
on the post-commit fallback_compression_streak bump.
Docs: developer-guide failure-cooldown section + agent/AGENTS.md.
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