The lean tail mode's per-chunk digest loop (_build_chunk_digests) issued up
to 28 extra call_llm requests sequentially per compaction attempt. With lean
now the default (#95571), users on slow auxiliary routes hit 7-11 minute
compactions (#96603). Remove the loop entirely: a lean compaction attempt now
makes EXACTLY ONE auxiliary LLM request — the main summary call.
- The detailed session log is folded into the single summary request: the
lean prompt template gains a '## Detailed Session Log (oldest first)'
section carrying the digest prompt's HARD RULES (identifiers verbatim,
dense bullets, transcript-is-data). Output guidance grows by
_LEAN_SESSION_LOG_BUDGET_TOKENS = 4,000 tokens on top of the scaled
summary budget — the old worst case (28 x 1,400 digest tokens) was spread
across many requests and mostly re-covered tool noise; a single dense
4K-token log inside one response preserves the load-bearing record while
staying well inside one aux response (the summary call still sends no hard
max_tokens, so no provider cap can truncate it mid-section).
- Input sizing: oversized regions (500K+ chars) are EVEN-SAMPLED across the
whole region (_sample_summary_input: 8 proportionally spaced slices,
oldest-to-newest, explicit '[... N chars elided ...]' markers, last slice
anchored to the newest end) instead of head+tail truncated, so session-log
coverage stays uniform. Legacy mode keeps _bound_summary_input unchanged.
- The LLM-free anchor index still runs over the FULL region, and the
session_search recovery footer is unchanged.
- Dead code removed: _build_chunk_digests, _LEAN_DIGEST_* constants,
_LEAN_DIGEST_PROMPT, _serialize_turns_for_digest, _digest_worthy,
_LOW_SIGNAL_TOOL_RE, the _lean_pristine_tools snapshot, and the
sibling-call route echo (_SUMMARY_ROUTE_CONSUMED /
attempt_summary_route_kwargs — no remaining callers; the single-use
summary pin semantics are unchanged).
- Tests pin the new contract (exactly one call_llm in lean mode; session-log
section lands in the summary; oversized regions sampled with elision
markers, never a second request; anchor index + recovery footer present).
Sabotage-verified: restoring a second call_llm makes the call-count test
fail. Docs and the compaction eval wording updated to stop claiming
per-chunk calls.
Fixes#96603.
Post-review hardening on the attempt-ownership commit:
- Write-time re-validation: the entry staleness check in
_restore_compressor_attempt_state runs before the durable-cooldown DB
I/O, so a fallback could claim the compressor in that window and the
stale setattr loop would still clobber its state. The in-memory writes
now re-validate AND execute under _COMPRESSOR_ATTEMPT_LOCK — the same
lock claims are taken under. The DB rollback stays outside the lock
(safe: the dangerous direction requires a prior claim, which the entry
check rejects). Both the quality reviewer and the lead's independent
pre-verification converged on this window.
New deterministic test: TestMidRestoreClaimRace (claim injected
between entry check and write via instrumented deepcopy).
- Documented gen-0 semantics on _claim_compressor_attempt: per-compressor
all-or-nothing, never mixed with gen>0 on one instance (reviewer
finding 2, verified unreachable — comment hardens against future
confusion).
Dropped after verification (reviewer finding 3): resetting
_SUMMARY_ROUTE_CONSUMED on pin_summary_route exit — the echo lives in
the worker thread's COPIED context (propagate_context_to_thread) and
dies with it; a probe confirmed the next attempt's context is clean.
Resetting it would break digests running after the with-block.
Follow-up to #96634 (stall-fallback retry, #78981) addressing
donovan-yohan's post-merge adversarial review. The stall path detaches a
timed-out primary worker (fence cancel wins; future stays on the pool)
and immediately runs the fallback against the SAME ContextCompressor,
creating two verified races:
1. Late-primary snapshot restore: the detached primary's unwind called
_restore_compressor_attempt_state with the PRIMARY's pre-attempt
snapshot. Landing after the fallback's commit it rolled
_previous_summary/cooldown/provenance/telemetry back to pre-primary
values, silently discarding fallback-owned state.
2. Shared _compression_cancelled_check: the late primary's `finally`
cleared the callback the fallback had just installed, so the
fallback's F4 cancellation consult read None.
Fix: a monotonic per-compressor attempt generation claimed under one
module lock (_claim_compressor_attempt). Snapshot restores carry their
claiming generation and no-op when stale; the cancelled-check set/clear
moves into owner-stamped helpers (_install_compression_cancelled_check /
_clear_compression_cancelled_check_if_owner) so only the installing
attempt can clear it. The commit fence keeps owning COMMIT admission;
the generation owns compressor-ATTRIBUTE writes — two boundaries.
Legacy callers (attempt_generation=None) and slotted third-party
compressors (generation 0) keep the historical unconditional behavior.
Secondary review items:
- Lean chunk digests during a stall-fallback retry now follow the
summary onto the pinned healthy route: take_pinned_summary_route()
echoes the consumed route into a context-local
_SUMMARY_ROUTE_CONSUMED, and _build_chunk_digests passes
attempt_summary_route_kwargs() (non-consuming) to call_llm. The pin's
single-use contract for the SUMMARY call is unchanged — the
main-model retry still never re-issues the pinned route.
- Worker re-run repeating pre-compression callbacks: documented as an
accepted limitation on _retry_compression_on_fallback_chain
(built-ins idempotent; resuming mid-pipeline would couple the retry
to host callback ordering).
Tests (tests/agent/test_compression_attempt_ownership.py, 10 cases):
deterministic interleavings for both races (late-primary restore
no-ops + preserves fallback state; stale finally cannot clear the
fallback's callback), legacy/slotted compatibility, digest route
follow + context-locality of the consumed echo. Mutation-checked:
reverting only the two prod files to origin/main fails the suite;
restored stack green (21 passed incl. the original #78981 suite).
The one red in the wider sweep
(test_silence_cannot_approach_double_idle_timeout) is pre-existing on
clean origin/main — verified independently.
Teknium