pin — compaction-proof context for Claude Code

A Claude Mod (function-hooks plugin). Wrap anything in <pin>...</pin> in your prompts and it will survive /compact, auto-compaction, plugin-triggered compaction, and precompute.

Usage

<pin>
The prod database is read-only until Friday. Never suggest migrations.
API base: https://api.internal.example/v2
</pin>

Now help me refactor the ingestion job.

Run with the mod loaded (Mods are early access and gated behind function hooks):

CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1 claude --plugin-dir ./pin-mod

How it works

• Hooks session.compact. On the way down it extracts every unique <pin> block from the transcript and appends an instruction telling the summarizer to preserve pinned content.
• On the way up (after the engine compacts), it appends a single "carrier" user message containing all pins, tags intact. Because the tags survive, the next compaction re-extracts them — pins persist indefinitely. Old carriers are dropped before a new one is appended, so nothing accumulates.
• An optional ui.render hook draws 📌 N pinned in the band above the prompt on the terminal surface.

Verify before trusting it

claude plugin validate ./pin-mod
CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1 claude plugin test ./pin-mod

Then in a throwaway session: pin something, generate filler conversation, run /compact, and confirm the pinned text is still in context (ask the model to repeat it, or inspect with /context).

Regenerate type declarations after any Claude Code update with /plugin-types — the API is early access and may change between releases without notice.

Known limits

• Hooks have a time budget; a hook that overruns is skipped and core compaction runs alone (your pins would be lost for that pass). This mod does no I/O beyond one transcript read, so it stays well under budget.
• Without CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1, the modules field in hooks.json is silently ignored — no error, no pinning.
• Pins are extracted from message text (user and assistant). Pins inside tool output are not scanned; move important tool findings into a pinned prompt line if you need them kept.
• The strip in ui.render is written against the AbovePrompt component of Claude Code 2.1.277's published types; if your build's contract differs, delete that block — the compaction hook is independent of it.