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fix(opencode): keep dynamic user.system separate for prompt caching by josiah-arcanist · Pull Request #20109 · anomalyco/opencode · GitHub

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fix(opencode): keep dynamic user.system separate for prompt caching - #20109

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fix(opencode): keep dynamic user.system separate for prompt caching#20109
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josiah-arcanist commented Mar 30, 2026 •
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Issue for this PR

Closes #20110

Type of change

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

What does this PR do?

Anthropic prompt caching misses because packages/opencode/src/session/llm.ts merges the session-static system prefix with per-turn user.system content before building the request. This PR keeps the static prefix in the first system message, sends dynamic user.system text as a separate second system message, and preserves that two-part shape after plugin system transforms. It also adds a regression test for the outbound Anthropic /messages payload.

This overlaps with #14203, #14743, and #19961. The scope here is intentionally narrow: only the session/llm.ts split plus the matching regression test.

How did you verify your code works?

  • bun test test/session/llm.test.ts
  • bun run typecheck

Screenshots / recordings

N/A (non-UI change)

Checklist

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

github-actions Bot commented Mar 30, 2026

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Hey! Your PR title [codex] fix anthropic prompt caching doesn't follow conventional commit format.

Please update it to start with one of:

  • feat: or feat(scope): new feature
  • fix: or fix(scope): bug fix
  • docs: or docs(scope): documentation changes
  • chore: or chore(scope): maintenance tasks
  • refactor: or refactor(scope): code refactoring
  • test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

github-actions Bot added needs:title needs:compliance This means the issue will auto-close after 2 hours. labels Mar 30, 2026

github-actions Bot commented Mar 30, 2026

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The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate PRs Found

The following related PRs address similar Anthropic prompt caching issues:

  1. fix: split system prompt into 2 messages for proper Anthropic prompt caching #14203 - "fix: split system prompt into 2 messages for proper Anthropic prompt caching"

  2. fix(cache): improve Anthropic prompt cache hit rate with system split and tool stability #14743 - "fix(cache): improve Anthropic prompt cache hit rate with system split and tool stability"

  3. fix(session): fire system.transform before messages.transform #19961 - "fix(session): fire system.transform before messages.transform"

These PRs appear to address the same root cause (system prompt merging affecting cache hits) with similar solutions (separating static and dynamic system content).

josiah-arcanist changed the title [codex] fix anthropic prompt caching fix(opencode): keep dynamic user.system separate for prompt caching Mar 30, 2026

josiah-arcanist commented Mar 30, 2026

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On the duplicate-PR bot note: this does overlap with #14203, #14743, and #19961. I kept this branch intentionally narrow to the session/llm.ts system split and the matching Anthropic regression test. If maintainers would rather consolidate on one of the older branches, I can close this PR.

github-actions Bot removed needs:title needs:compliance This means the issue will auto-close after 2 hours. labels Mar 30, 2026

github-actions Bot commented Mar 30, 2026

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

josiah-arcanist marked this pull request as ready for review March 30, 2026 18:28

josiah-arcanist commented Mar 30, 2026

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cc @kommander for viz

sendhil-anduril added a commit to sendhil/opencode that referenced this pull request Apr 2, 2026
fix(prompt): keep dynamic user.system separate for prompt caching (up…
bfb6cda 
…stream PR anomalyco#20109)
github-actions Bot mentioned this pull request Apr 8, 2026
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Anthropic prompt caching misses when dynamic user.system is merged into the static prefix

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