## Summary
- Added `isCompactableTool()` helper in `microCompact.ts` that matches
both the existing COMPACTABLE_TOOLS set and any tool prefixed `mcp__`
- MCP tool results were never compacted because the hardcoded allowlist
only contained 9 built-in tools — MCP tools fell through and persisted
in full for the entire session, wasting 10-500K tokens/session
## Impact
- user-facing impact: long sessions using MCP servers (GitHub, Slack,
Playwright, etc.) will compact stale MCP tool results, reducing token
usage and delaying autocompact triggers
- developer/maintainer impact: new MCP servers are automatically covered
via prefix match — no need to update the allowlist per-server
## Testing
- [x] `bun run build`
- [x] `bun run smoke`
- [x] focused tests: `bun test src/services/compact/microCompact.test.ts`
- module exports load correctly
- estimateMessageTokens counts MCP tool_use blocks
- microcompactMessages processes MCP tools without error
- microcompactMessages processes mixed built-in and MCP tools
## Notes
- provider/model path tested: n/a (compaction logic is model-agnostic)
- screenshots attached (if UI changed): n/a
- follow-up work or known limitations: subagent results and thinking
blocks are still not compacted (separate RFCs)
https://claude.ai/code/session_01D7kprMn4c66a5WrZscF7rv
Co-authored-by: Claude <noreply@anthropic.com>
