Compaction can reuse an oversized request and leave only 1024 output tokens #62943

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1. opencodejr commented on Nov 9, 2026

   

   opencodejrBot

   on Nov 9, 2026

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   Thanks for the precise report. I reproduced this with your unit test on the latest dev (7524e5f). Compaction completes, but the summary request is sent with maxTokens = 1024 instead of the fixture's 25000.

   On the v2.2.5 tag the same test can't show it: the test model there has no output limit, so maxTokens is undefined. The code involved is the same in that release.

   The cause is as you describe. With no retained tail, withoutTail() returns prepared.request itself. In deliver(), that request fails the measured check, then passes the character-estimate check as shrink.history. Because it is the same object, the measured size still reaches fitOutput(), which cuts the output allowance instead of taking the text fallback.

   The script below adds your test, runs it against a checkout and restores the file. Related: #62944 (targeted fix) and #59951 (broader context-budget rewrite).

   Reproduction script (repro.sh)

   #!/usr/bin/env bash
   # Reproduces #62943: compaction reuses an oversized measured request and cuts the
   # summary's output allowance to 1024 tokens instead of taking the text fallback.
   # Usage: repro.sh <path to opencode checkout> (dependencies installed with `bun install`)
   set -euo pipefail
   REPO="${1:-/workspace/repo}"
   cd "$REPO/packages/core"
   TEST=test/session-compaction.test.ts
   cp "$TEST" /tmp/session-compaction.test.ts.bak
   trap 'cp /tmp/session-compaction.test.ts.bak "$TEST"' EXIT
   cat >> "$TEST" <<'EOF'
   
   it.effect("repro #62943: summary keeps output room despite a low character estimate", () =>
     Effect.gen(function* () {
       const fixture = yield* summaryFixture([
         textUser("Latest question"),
         measured("Latest answer", summaryWindow - 1024),
       ])
       expect(yield* fixture.run()).toEqual({ status: "completed" })
       console.log("REPRO maxTokens =", requests[0].maxTokens, "expected summaryBuffer =", summaryBuffer)
       expect(requests[0].maxTokens).toBe(summaryBuffer)
     }),
   )
   EOF
   bun run script/test.ts "$TEST" -t "repro #62943" 2>&1 | grep -E "REPRO|pass|fail|Expected|Received|error" | head -20

   Run it: bash repro.sh
2. opencodejr

   added

   reproduced

   on Nov 9, 2026