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refactor(session): stop excerpting the same tail turn twice in turnCost - #1407
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turnCost excerpted the same tail turn twice per pick: once directly and once through excerptedTurnTokens, which re-ran excerptTailTurn. The closure token estimate excerpted picked turns a third time. Cache the first excerpt per turn in selectTail and reuse it for the closure estimate, turnCost's token count, and the emitted live copies. Adds a test seam counter (excerptTailTurnCallCount) and a proof test pinning one excerptTailTurn call per tail turn with identical values.
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Stops excerpting the same tail turn twice inside one selectTail pass by caching the first excerpt.
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CL-10535 — Stop excerpting the same tail turn twice in compactor turnCost
Fix
selectTailexcerpted the same tail turn multiple times per pass:turnCostcalledexcerptTailTurndirectly, thenexcerptedTurnTokens, which calledexcerptTailTurnagain (the reported double-excerpt inturnCost).excerptedTurnTokenson raw turns, so picked closure turns were excerpted a third time.The fix caches the first
excerptTailTurnresult per turn inselectTail(excerptFor+excerptCache) and reuses it for the closure token estimate,turnCost's token count, and the emitted live copies.excerptedTurnTokensis replaced byliveTurnTokens, which counts tokens over an already-excerpted turn and never re-excerpts. Behavior and values are identical (tests pin).Proof test
src/session/compactor-excerpt-once.test.ts— a newexcerptTailTurnCallCounttest seam countsexcerptTailTurninvocations; the test asserts a full compactor pass over N tail turns callsexcerptTailTurnexactly N times (once per turn), while all oversized tool outputs are still head+tail excerpted with identical values.Verification
bun test src/session/compactor-excerpt-once.test.ts— 1 passcompactor-pairing.test.ts,compaction-verify.test.ts,compaction-archive.test.ts,compaction-handoff.test.ts,summarizer.test.ts,summarizer-excerpt.test.ts,context-compactor.test.ts) — 173 pass, 0 failbun run typecheck— exit 0oxfmt --check+oxlinton changed files — cleanbun run check:dead-exports— 0 violationsDiff stat
src/session/compactor.ts+30 −14,src/session/compactor-excerpt-once.test.ts+104 (new).