fix(compression): warn the user when compression is blocked but context keeps growing

[teknium1]

Summary

When a session's context crosses the compression threshold but automatic compression is blocked (summary-LLM cooldown or the anti-thrash breaker), the user now gets a visible, deduped warning telling them to run /new or /compress — instead of the session silently growing until it dies at the hard provider token limit. Root cause: should_compress() returns a bare False on the veto paths and every guard only logger.info'd the skip, so the failure mode was invisible from chat (the warning half of #62708).

Changes

• agent/context_compressor.py: should_compress_info() returns (bool, reason) (cooldown:<s> / ineffective); on current main's refactored gate it derives the reason from the same in-memory state via a new _compression_block_reason() helper. should_compress() keeps its bool contract.
• agent/context_engine.py: backward-compatible ABC default should_compress_info() → (should_compress(tokens), None) so plugin engines never raise AttributeError (follow-up: the PR's default had no return statement — it returned None and would have crashed tuple-unpacking call sites).
• run_agent.py: centralized AIAgent._warn_context_overflow_blocked() / _clear_context_overflow_warn() — dedup keys on the block kind so a ticking cooldown doesn't re-fire every turn.
• agent/turn_context.py + agent/conversation_loop.py: all three automatic-compression guards (preflight, pre-API, post-tool loop compaction) warn when blocked-over-threshold, and every compression path resets the dedup — closing the sweeper-review gap where the block clearing while still over threshold entered the compression branch and skipped the else reset, suppressing the warning forever after.
• Below-threshold guard (follow-up): the persisted-cooldown branches no longer warn when the estimate is under threshold, and the pre-API guard honors compression.max_attempts instead of a hardcoded 3.
• agent/conversation_compression.py: warning text is a template constant (CONTEXT_OVERFLOW_BLOCKED_WARNING_TEMPLATE) marked FAILURE-CLASS — deliberately not in ROUTINE_COMPRESSION_STATUS_SAMPLES or the noise regex; wording composes with fix(compression): floor the threshold recommendation at the effective small-context minimum #69332's recomputed-trigger notice (no contradictory threshold advice, just /new / /compress).
• tests/: PR's suite (tuple shape, both block kinds, dedup, re-fire) + follow-up tests: dedup-reset-while-still-over-threshold, below-threshold cooldown no-warn, plugin-engine ABC default, and noise-filter survival tests that execute the real _TELEGRAM_NOISY_STATUS_RE (fix(gateway): suppress routine pre-API compression chatter on chat platforms #69550-widened) and _prepare_gateway_status_message end-to-end; both reason shapes pinned un-swallowed in VISIBLE_COMPRESSION_MESSAGES.

Validation

	Before	After
Over threshold, compression blocked	bare False, logger.info only — user sees nothing until token-limit death	deduped ⚠ warning in chat with /new / /compress guidance
Block clears while still over threshold	dedup never reset — warning suppressed forever after first block	reset on every compression path; warning re-fires on next block
Plugin engine at the new call sites	AttributeError (contract only required should_compress)	ABC default returns (should_compress(tokens), None)
Warning vs gateway noise filter	unverified against #69550-widened regex	pinned un-swallowed on every chat platform

Targeted tests: 630 passed (overflow-warning suite ×19, turn-context ×18, telegram noise filter ×587, plugin engine init ×6); -k 'blocked or overflow_warn or should_compress_info' sweep: 532 passed, 0 failed; sibling compressor suites (rotation state, idle compaction, context compressor, feasibility): 246 passed.

Credit

Salvaged from #62625 by @sl4m3. Addresses the warning half of #62708.

Infographic

[github-actions]

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[alt-glitch]

This was generated by AI during triage.

Related: #62625 already proposes blocked-compression warning plumbing for #62708. This patch has additional current-head follow-ups; both solve the same user-visible warning goal, so maintainers should choose or consolidate rather than treat either as a duplicate.