Problem

vp migrate removes Prettier itself, but a migrated project keeps installing dead Prettier
packages under most naming shapes. rewritePrettierPackageJson matched only the exact name
prettier and the flat prettier-plugin-* prefix, so all of these survived migration:

• scoped plugins — @trivago/prettier-plugin-sort-imports, @ianvs/prettier-plugin-sort-imports,
  @shopify/prettier-plugin-liquid
• the official @prettier/ scope — @prettier/plugin-php, @prettier/plugin-xml,
  @prettier/plugin-ruby
• shareable configs — prettier-config-*, @scope/prettier-config
• @types/prettier

The asymmetry looks arbitrary rather than intentional: unscoped prettier-plugin-sort-imports is
removed, while the scoped package of the same name is not.

The sibling ESLint path already gets this right. isEslintEcosystemDep in
migrator/eslint.ts recognises named packages, flat prefixes, whole scopes, the scoped
^@[^/]+\/eslint-(plugin|config|formatter)(-.+)?$ form, and treats @types/NAME symmetrically
with NAME.

Changes

Adds isPrettierEcosystemDep mirroring isEslintEcosystemDep, and routes both dependency loops
through it.

The matched set is deliberately narrow, and a test pins that: eslint-config-prettier,
eslint-plugin-prettier, prettierx, and an unrelated @prettierx/ scope are all preserved.

Also deliberately unchanged:

• the fields scanned. peerDependencies and optionalDependencies are still left alone. The
  ESLint path does scrub them, but whether migration should silently drop a declared peer
  dependency is exactly what a P1 on feat(migrate): preserve dynamic Oxlint and Oxfmt configs #2483 is currently about, so I have not imported that decision
  here.
• empty containers. The ESLint path deletes a dependency field it empties; this one still
  leaves "devDependencies": {}. Same reasoning — separate concern, separate PR if wanted.

rewritePrettierPackageJson becomes exported. migrator/README.md rule 1 asks for module functions
to be exported so the barrel surfaces them, and it makes the function unit-testable exactly like
rewriteEslintPackageJson.

Testing

Six cases added to migrator.spec.ts, next to the rewriteEslintPackageJson block and following
its conventions.

Verified in both directions: with the old matcher restored and the new tests kept, 4 fail;
with the fix, 6/6 pass. The two that pass either way are the guards for behaviour that is meant
to be unchanged (unrelated-name preservation, and the no-op case).

Checks actually run:

• migrator.spec.ts — before/after diffed in the same build state: identical failure set both
  ways (139), with the change adding exactly 6 passing tests (206 → 212).
• oxlint@1.79.0 (the repo's pin) with -D correctness -D perf -D suspicious on both changed
  files — no new findings. The one reported error is pre-existing and byte-identical on the
  unmodified files, and is a rule this repo sets to off in vite.config.ts.
• oxfmt@0.64.0 (the repo's pin), configured from this repo's fmt block — clean, and clean on
  untouched control files too.
• git diff --check — clean.

Not run: vp check, pnpm test:unit, tsgo, and the PTY snapshot suite, which need a full
workspace build my environment cannot produce. No PTY fixture covers rewritePrettierPackageJson,
and this change adds no CLI output.

AI assistance

Claude Opus 5 wrote the implementation, the tests, and this description. The change is
agent-authored and has not had a separate human review. Every result quoted above is from an actual
run, not an estimate.