feat(upstream): check the upstream migration history against upstream

[incognitojam]

Note

Fork CI and the upstream intake audit now fail when the upstream migration manifest or migration files differ from upstream, so a fork migration can no longer take an upstream migration ID.

Fork #538 added its ProjectionThreadLatestMessageAt migration to the upstream manifest as ID 51. Upstream uses 51 for ProjectionThreadMessageContext, and because the migrator treats the highest recorded ID as a watermark, databases that ran the fork migration would have skipped upstream's. Nothing caught this until the next intake conflicted with it, after two nightlies had shipped it (fixed in #550).

Change

• vp run --filter @t3tools/scripts migrations:check compares apps/server/src/persistence/Migrations.ts and everything under apps/server/src/persistence/Migrations/ with fetched upstream main:
  • the fork's manifest must be a prefix of upstream's, with the same ID, name and module at each position. A fork-only entry, a renamed entry, or a later upstream migration imported without the earlier ones fails;
  • every file must match a version upstream has had at that path, so upstream edits to its own tests do not cause failures while the fork trails.
• Fork Check fetches upstream main and runs the check on every pull request and push.
• The intake audit runs the same check on the candidate and reports mismatches as blocking errors. The Fork CI intake job and the promotion workflow fetch upstream main before the audit.
• The audit's "a database migration changed" review reason now names what changed, for example a database migration changed: adds 50 ProjectionThreadPullRequests.
• docs/internals/fork-migrations.md describes the check. An early import of an unmerged upstream migration fails it until upstream merges the migration, since its ID can still change before then.

Validation

• Current main passes. The check takes about a tenth of a second.
• The feat(clients): choose thread activity timestamp #538 commit fails with four errors, including Upstream migration manifest position 51 is 51 ProjectionThreadLatestMessageAt (…), but upstream has 51 ProjectionThreadMessageContext (…).
• Across main, only the commits from feat(clients): choose thread activity timestamp #538 up to fix(server): move the latest message migration into fork history #550 fail. The 250 commits before feat(clients): choose thread activity timestamp #538 all pass, including the intakes that brought migrations 49 and 50.
• The intake audit on feat(clients): choose thread activity timestamp #538 alone reports Blocked with the migration errors and a database migration changed: adds 51 ProjectionThreadLatestMessageAt. On the upstream feat(pull-requests): link multiple pull requests to threads pingdotgg/t3code#10839 intake commit (feat(pull-requests): link multiple pull requests to threads pingdotgg/t3code#10839) it reports a database migration changed: adds 50 ProjectionThreadPullRequests without errors.
• New unit tests cover manifest parsing, the prefix rule, file matching, change descriptions and the audit integration, and assert that each workflow fetches upstream before its check. The upstream script tests, scripts typecheck and lint of the changed files pass.
• Not yet run: the new Fork Check step in GitHub Actions. This pull request's own CI exercises it.

---

Written by an agent (Claude Code, claude-opus-5-5).