[TheFabFab]

Two changes to compaction, both from production bug reports of 2026-10-22 (21:09) where a compacted mentor chat lost its project files and got a summary that contradicted the messages after it.

1. Carry. experimental.session.compacting now receives messages — the messages created before the retained tail starts, i.e. those leaving the model's view, in model order — and may return carry: string[]. Once the summary succeeds, each carried text is stored as a synthetic text part (metadata.compaction_carry) on the compaction's user message. The model reads it before the summary from the auto-continue turn on, and completedCompactions already hides that message from every later summariser, so it is never paraphrased. A tail can reach back past an earlier compaction message, which then stays in view; it is not handed to the hook, so nothing is carried twice. DocuMentor's plugin (TheFabFab/KPG) carries its PROJECT.md, MEMORY.md, knowledge-base index and WORKSPACE.md blocks.

2. The summariser reads the retained tail. It was shown only the head, so two helper results and a retried action that landed in the tail left the summary saying "two background tasks running, archive move failed". buildPrompt takes retained; the prompt shows the tail in <retained> after the conversation, with the instruction not to summarise it and to write Work State and Next Move as the state after it.

Tests

• documentor: carries plugin text verbatim … (compaction.test.ts): stored, seen by the model before the summary, absent from the second summariser's input, handed to the second compaction's hook. Fails without the change.
• Upstream's tail tests now assert the tail stays out of <conversation> and appears in <retained>.
• End to end, compiled binary over ACP with DocuMentor's plugin and a fake OpenAI-compatible provider recording every request, three forced compactions: the auto-continue request after each holds each project file exactly once (before its summary where the carrier is the new compaction message), later summarisers never see them, and the first summariser reads the kept turn in <retained>, not in <conversation>. The same run against a binary without this change fails the six carry checks.
• FORK.md rows added.

🤖 Generated with Claude Code

https://claude.ai/code/session_0148RPMT9kUkZ6BL4TtebZJe

[github-actions]

Hey! Your PR title Compaction carries plugin text verbatim on the compaction message 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
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• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

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