Third correction, and the load-bearing one. The previous commit put the
"did compaction clear the threshold?" verdict inside should_compress(). But
conversation_loop calls should_compress() TWICE per turn with two different
measures (turn_context.py / conversation_loop.py:1033 and :4789):
* pre-API : request_pressure_tokens -- a rough estimate that can dip BELOW
the threshold
* post-API: real prompt tokens -- which stay above it
So the rough reading reset the strike every turn and the loop never stopped.
Reproduced: 8 compactions in 8 turns under the real two-call pattern, even
with the previous fix applied. (My earlier repro only called should_compress()
once per turn, which is why it looked contained.)
Move the verdict to update_from_response(), the one place that sees the
provider's real prompt_tokens for the just-compacted conversation, guarded by
the existing awaiting_real_usage_after_compression flag so it fires exactly
once per compaction. Real-vs-real: it cannot be fooled by a rough sub-threshold
reading, and (from the previous commit's lesson) never subtracts an estimate
from a real count. should_compress() goes back to a plain threshold test plus
the pre-existing cooldown and anti-thrash guards.
New test test_rough_preflight_reading_does_not_reopen_the_loop drives the real
two-call-per-turn pattern and fails on the prior should_compress()-based commit.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Follow-up to the previous commit, whose futility check was unsound:
incompressible_floor = max(0, display_tokens - pre_estimate)
`display_tokens` is the provider's real prompt count; `pre_estimate` is
`estimate_messages_tokens_rough(messages)`. Subtracting an estimate from a real
count folds the tokenizer skew into "floor" and misreads it as incompressible
overhead. With a 1.6x skew on a 200K window (threshold 150K, true floor 30K):
rough_msgs=253,804 real_prompt=436,086
computed floor = 182,282 <-- mostly skew; exceeds the threshold
after compaction: 401 -> 77 msgs, real prompt = 106,361 (CLEARS 150,000)
verdict: ineffective_count = 1 <-- false positive
Two such passes would permanently disable compaction on a healthy session --
worse than the loop this PR set out to fix.
Move the check into should_compress(), where both sides of the comparison are
the caller's own token count:
* prompt under the threshold -> not thrashing; reset the counter
* a compaction just ran and we are STILL over -> one strike
Real-vs-real, so tokenizer skew can never be mistaken for a floor, and nothing
subtracts an estimate from a real count. compress() now only ever increments the
counter; the reset lives with the one measure the trigger uses.
Adds `test_no_false_positive_under_tokenizer_skew` (the case above) and
`test_counter_resets_once_the_prompt_fits_again` (one failed pass must not
disable compaction forever). Against upstream, 5 of the 7 cases fail; the 2 that
pass are the regression guards, which is the intended shape.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
`should_compress()` documents anti-thrashing protection ("if the last two
compressions each saved less than 10%, skip compression to avoid infinite
loops"). In practice `_ineffective_compression_count` reset on every pass,
so the guard was dead code and a mis-sized context window presented as a
hung CLI instead of a warning.
Two defects:
1. Mixed measurement bases. Effectiveness was
`(current_tokens - estimate(compressed)) / current_tokens`, where
`current_tokens` is the provider's FULL prompt (system prompt + tool
schemas + messages) but `estimate(compressed)` covers messages only.
Every compaction therefore reported ~96% savings and reset the counter.
Savings is now scored messages-vs-messages.
2. Message shrinkage is the wrong yardstick. `should_compress()` trips on
the full prompt, but compaction can only shrink messages -- the system
prompt and tool schemas are an incompressible floor. When that floor
alone meets the threshold, each pass shrinks messages by a healthy
margin, legitimately resets the counter, and still leaves the prompt
over the line; the next turn compacts again, forever. Observed in the
wild: 45+ consecutive compactions, one auxiliary-LLM call each, zero
progress. Effectiveness is now scored against the goal -- did the
projected prompt get under the threshold? -- and a futile pass warns
with the numbers that prove it.
Also record an ineffective pass on the "only N messages (need > M)" early
return, which previously returned the transcript unchanged without moving
any anti-thrash state -- the same class of bug the neighbouring
"no compressable window" branch was already fixed for.
Tests: 4 of the 5 new cases fail on main and pass here; the fifth pins
that effective compaction still resets the counter (121 -> 15 messages,
88.9% savings).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
