Idle compaction (`compression.idle_compact_after_seconds`) skipped work only
when the context was at or below `threshold_tokens × summary_target_ratio`.
That is a *theoretical* post-compaction target: a real pass lands well above
it because the system prompt, the tool schemas and the protected head/tail
are an incompressible floor.
So a session that compacted to well above the target stayed above it forever,
and every later idle resume re-ran a full summarisation over a transcript that
had not grown. In the reported session the 17:01 pass reduced 64,105 -> 44,579
tokens; the 17:36 resume re-fired because 44,579 was still above the 25,502
theoretical floor, blocking the prompt for another 256 s on a ~55 tok/s local
route and reclaiming nothing. Neither pass was followed by a single API call.
`_should_idle_compact` now also honours `last_compression_rough_tokens` — what
the previous pass on this session actually produced, recorded by
`compress_context` with the same `estimate_request_tokens_rough` shape the idle
estimate uses. When it is known, the transcript must accumulate at least one
`floor_tokens` worth of new content on top of it before another pass is worth
its wall clock. A raised floor is a deferral, not an off switch.
`0` — nothing compacted yet, or the counter cleared by a rebind/recalibration
— keeps the original semantics exactly, so the first idle compaction of any
session is unaffected. The call site type-pins the read so compressor doubles
that expose a Mock there fall back to the original floor.
Fixes a root cause behind #97239. Deliberately does not touch the TUI status
surface (#97253), the digest chain / total ceiling (#93241), or turn-settle
scheduling (#96891).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HV3k1v5nx9ag5d5wXSFZ7o
Long-lived sessions (e.g. a Telegram thread resumed over hours/days)
accumulate a large context that the existing size-based threshold only
trims once it crosses `threshold × context_window`. Until then every
turn re-reads the full history, which on large-context models can mean
hundreds of K of cache-read tokens per call even across long idle gaps.
Add a time-based trigger that complements (does not replace) the size
threshold: when a session resumes after `compression.idle_compact_after_seconds`
of inactivity, compact the accumulated history up front, before the first
reply. Disabled by default (0), so existing behaviour is unchanged.
The trigger reuses `_last_activity_ts` (the last time the turn loop did
work) to measure the idle gap at turn start, gates the token estimate
behind a cheap gap pre-check, and skips compaction when the context is
already at/below the post-compression target (threshold × target_ratio)
so a short idle thread never pays for a summarization that saves nothing.
It also defers to an active compression-failure cooldown.
The decision is factored into a pure predicate, `_should_idle_compact`,
which is unit-tested without a live agent.
joaomarcos