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fix(compaction): place summary instruction after conversation history by akenra · Pull Request #42012 · anomalyco/opencode · GitHub

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fix(compaction): place summary instruction after conversation history - #42012

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fix(compaction): place summary instruction after conversation history#42012
akenra wants to merge 1 commit into
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akenra:fix/compaction-prompt-ordering

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akenra commented Aug 12, 2026 •
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Issue for this PR

Closes #41801
Refs #41268
Refs #41358
Refs #36682

Type of change

  • Bug fix
  • New feature
  • Refactor / code improvement
  • Documentation

What does this PR do?

/compact (and auto-compaction) sends the summarization request as one user message: summary instruction first, then the serialized conversation. The conversation is formatted as a chat log ([User]: / [Assistant]:) and ends with a real user question from the past session, so the model answers that old question (or reproduces the transcript) instead of producing the summary — the instruction at the start is diluted, especially on 1M-context models like opencode-go/deepseek-v4-flash where the whole session fits.

The summary template itself says "using the conversation history above", i.e. history-first was the intended layout; the call site inverts it.

Change: put the conversation first, then "End of conversation history.", then the summary instruction + template, ending with an explicit guard that the history is reference material only and only the anchored summary must be output. Applied to both paths:

  1. packages/opencode/src/session/compaction.ts — manual /compact and CLI auto-compaction.
  2. packages/core/src/session/compaction.ts — runner/make() auto-compaction.

The experimental.session.compacting plugin hook still works; a plugin-provided prompt now lands after the history.

How did you verify your code works?

  • tsgo --noEmit typecheck passes for packages/opencode and packages/core.
  • New regression test session.compaction.process > places the summary instruction after the conversation history in packages/opencode/test/session/compaction.test.ts asserts the history precedes the instruction and that the guard line is the last content after any [User]: turn.
  • Full test/session/compaction.test.ts (54 pass), test/session/revert-compact.test.ts (8 pass) and packages/core/test/session-compaction.test.ts (2 pass) run green.
  • oxlint on both changed source files: 0 warnings, 0 errors.
  • Manual verification on a long session with opencode-go/deepseek-v4-flash (1M context): /compact now returns the anchored summary instead of answering the last question from the session.

Screenshots / recordings

Not a UI change.

Checklist

  • I have tested my changes locally
  • I have not included unrelated changes in this PR

github-actions Bot added needs:compliance This means the issue will auto-close after 2 hours. and removed needs:compliance This means the issue will auto-close after 2 hours. labels Aug 12, 2026

github-actions Bot commented Aug 12, 2026

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Thanks for updating your PR! It now meets our contributing guidelines. 👍

akenra commented Aug 12, 2026 •
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Runtime verification (reported by PR author):

Tested on OpenCode Desktop 1.18.16 (Windows) with opencode-go/deepseek-v4-flash (1M context). The same prompt-layout patch was applied directly to the Desktop bundle (app.asar) for testing.

Result: a ~350K-token session that previously would not compact correctly (the model answered an old question from the conversation instead of summarizing) now produces the proper anchored summary (## Objective / ## Important Details / ## Work State / ## Next Move / ## Relevant Files) via /compact.

This confirms the ordering fix resolves the reported behavior on the exact model/stack from #41801.

akenra force-pushed the fix/compaction-prompt-ordering branch from 03a7154 to fe5962e Compare August 12, 2026 14:49
akenra force-pushed the fix/compaction-prompt-ordering branch from fe5962e to 5284e2d Compare August 12, 2026 14:51

rekram1-node commented Aug 12, 2026

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Yeah the smaller models are having issues, ty for pr going to do a bit more cleanup but ill add u as a coauthor on my version

rekram1-node commented Aug 12, 2026

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going to go w/ this PR instead (added u as a coauthor):
#42045

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Successfully merging this pull request may close these issues.

Manual /compact with DeepSeek V4 Flash degenerates into thousands of repeated lines

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