fix(compressor): decay head protection across compression cycles#12092
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truenorth-lj wants to merge 1 commit into
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fix(compressor): decay head protection across compression cycles#12092truenorth-lj wants to merge 1 commit into
truenorth-lj wants to merge 1 commit into
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After the first compression, reduce head protection from protect_first_n to 1 (system message only). Previously, the first N messages were preserved verbatim across every compression cycle, causing "fossilized" messages that survived indefinitely even after being summarized. The system message (index 0) is always preserved. User/assistant messages in positions 1..protect_first_n are only protected during the first compression — subsequent compressions include them in the summarization window since their content is already captured in the summary. Closes NousResearch#11996 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Thanks for flagging @alt-glitch. After reading #9199, I think these are complementary rather than competing — they fix two different sub-cases of HEAD fossilization:
Concretely, even after #9199 lands, a long session with a system prompt and Happy to rebase on top of #9199 once it lands, or fold both fixes into a single PR if a maintainer prefers. |
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Summary
protect_first_nto 1 (system message only) so old user/assistant messages become eligible for summarization instead of surviving every compression cycle indefinitelyChanges
agent/context_compressor.pycompress(), compute_effective_headbased oncompression_count— fullprotect_first_non first compression, decays to 1 on subsequent compressions_min_for_compressto use the effective head counttests/agent/test_context_compressor.pyTestHeadProtectionDecayclass with 5 tests:test_first_compression_preserves_full_head— verifies original behavior on first compressiontest_second_compression_decays_head_protection— verifies fossilized messages are included in compression windowtest_system_message_always_preserved— verifies system prompt survives all compressionstest_protect_first_1_no_decay— edge case when protect_first_n=1test_multiple_compressions_dont_fossilize— end-to-end 2-cycle simulationTest plan
Closes #11996
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