[henrychu04]

Records three lessons from the 67661cf → 6d450a4 sync (PRs #277–#282) in docs/internals/sync.md:

• New callers of replaced functions. An upstream rewrite can add a new caller of a function a fork seam replaces, in a file that merged cleanly. feat(web): simpler composer with grouped controls, effort words and no collapsed state pingdotgg/t3code#25869's new-thread permissions label in ChatView.tsx did this; the Fable review found it. After resolving, rg for the upstream names each touched seam replaces.
• Fork wording breaks new upstream tests. Fork wording inside upstream code, like GitLab's "merge request !N", breaks new test cases upstream adds for that code (fix(server): threads settle right away when a watched PR merges pingdotgg/t3code#26395). pnpm test:coder stops at the first failing package, so rerun until every package has run.
• Removed surfaces belong in the resolve script. A modify/delete that sync-resolve-deleted.mjs leaves for a human on a surface the fork already removed should be added to DELETED_PATHS in the same stage.

Docs only.

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