Rename-day rollback runbook

[moosebay]

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Description

Adds announcement/rollback.md: the rollback runbook for the Oct 13, 2026 Stresseur rename, in case the new release needs to be pulled back per the owner's rule ("delete the new release or set it back to draft so nothing serves it, then ship a fix").

It covers five surfaces, each with exact gh/git commands and a way to confirm the rollback actually worked, verified against this repo's current code:

• Desktop auto-update (apps/desktop/src/main/update.ts, index.ts): drafting the release is sufficient to stop the offer, but main's package.json should still be reverted for hygiene; already-updated users have no auto-downgrade path and must reinstall by hand.
• install.sh: drafting the release is not sufficient — it breaks the installer outright with no fallback for a stable-looking version string. Reverting apps/cli/package.json on main is required, not optional.
• actions/run-flows with version: latest: resolves off git tags, not the Releases API, so drafting the release changes nothing here — the tag itself has to be deleted.
• The Studio data-folder migration: the current migrateDataDir() is copy-only and never touches the source directory, so a rollback to 1.1.x should recover pre-upgrade data untouched; work done only under the new build is lost until the fix ships. Includes suggested user-facing wording.
• Chrome extension (API Recorder): scope-corrects the premise — the extension itself isn't being renamed, only a string constant — then covers the publish pipeline (PlasmoHQ/bpp) and flags what's unverifiable about the Web Store dashboard's own rollback/staged-rollout behavior.

Everything not backed by code that exists in this repo today — most notably the rename PR itself (not yet merged) and the Chrome Web Store dashboard, which this repo can't inspect — is explicitly marked UNVERIFIED rather than asserted.

Nothing in this PR touches any release, tag, or workflow; it's documentation only, for the owner to execute by hand on the day.

References

None.

Testing

Documentation-only change. Every mechanism described was verified by reading the cited file/line in this checkout (update.ts, index.ts, install.sh, actions/run-flows/scripts/*.sh, apps/api-recorder-extension/{brand,build}.ts, .github/workflows/*.yaml, docs/release/prerelease.md) rather than assumed; claims that couldn't be checked against this repo's code are called out as UNVERIFIED inline.

Checklist

• I have added a Version Plan for new/changed functionality in this PR — N/A, docs-only addition under announcement/, no project version changes.
• All checks for formatting and tests are passing