The PM<->Markdown converter and its lib are duplicated the same way as the
AI-chat tool definitions: a copy lives in packages/mcp/src/lib (without
canonicalize.ts), another in docmost-sync's docmost-client lib (with
canonicalize + the no-comment-threads markdown-document mode), and the
git-sync integration plan vendors a third copy into packages/git-sync.
Record the already-observed drift (collaboration.ts ~329 changed lines,
etc.) and the docmost-schema vs @docmost/editor-ext schema-divergence risk,
and tie it to the existing single-source-of-truth fix direction.
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