The TS test suite is broken on main — many (all?) open PRs are red

Since #12747 merged (72b1927856, 2026‑07‑02), the TS test suite fails for many (possibly all?) PRs rebased onto main, in a way that appears unrelated to what the PR changes. The failures are in the test registry-mock.

Examples (all unrelated PRs, all failing the same way):

• feat(install): warn when an override matches no dependency #12741 — failing job
• fix(default-reporter): restore ansi-diff to stop duplicated output lines #12698 — failing job
• fix: make why --exclude-peers skip peer dependency edges #12763 — failing job
• perf(npm-resolver): normalize non-abbreviated registry metadata before caching #12766 — failing job

What the failure looks like

Two distinct symptoms, both from the mock registry.

1. Publishing a dist-tag to a proxied package is rejected (test/update/interactive.ts):

Failed to set dist-tag "latest" on package: 400 Bad Request.
Bad request: cannot publish "is-negative" to the path-less base:
it routes to an upstream registry; name a hosted mount
  at setDistTag (../../registry-access/client/src/setDistTag.ts:46:9)
  at addDistTag (../../testing/registry-mock/src/index.ts:49:3)
  at Object.<anonymous> (test/update/interactive.ts:79:3)

2. A scoped name that isn't a seeded fixture now 404s (test/update/recursive.ts):

GET http://localhost:<port>/@zkochan%2Fasync-regex-replace: Not Found - 404
  at RetryOperation._fn (../../resolving/npm-resolver/src/fetch.ts:169:16)

Both reproduce locally after building the current pnpr/pnpr-prepare and running e.g. installing/commands' jest.

Blast radius: the ubuntu chunk only runs installing/commands (2 files). The Windows chunks run pnpm/test and surface ~25+ failing files — publish/*, unpublish, dist-tag, deprecate, dlx, store/*, search, patch*, lockfile, install/*, update/*, … i.e. everything that publishes to, or reads an unseeded name from, the mock.

Root cause (AI-generated)

#12747 switched pnpr to the single-origin mount model: one declared origin per package, no cross-origin fall-through, and writes only to hosted mounts. The test registry's config.yaml (pnpr/crates/pnpr/config.yaml) previously carried a ** package policy with proxy: npmjs and publish: $authenticated, which let the JS tests do two things that are no longer possible:

• Overlay dist-tags/publishes onto upstream-proxied packages. addDistTag({ package: 'is-negative', ... }) targets the path-less base, which now routes to the npmjs upstream mount; resolve_publish_target (pnpr/crates/pnpr/src/server.rs:2269) rejects it. is-negative/is-positive/micromatch/foo/lodash/es5-ext/es6-iterator aren't seeded fixtures — only create-touch-file-one-bin and 8 @… scopes are in pnpr/.fixtures/packages.
• Proxy reads for unseeded scoped names. The new main router sends whole scopes (@zkochan/*, @scoped/*, …) to the local hosted mount, but only some names in each are seeded. @zkochan/ seeds only test-pnpm-issue219, so @zkochan/async-regex-replace 404s with no fall-through to npmjs.

The #12747 commit message states "registry-mock keeps working with no task or seed changes" — that's the incorrect assumption.

Why CI didn't catch it (AI-generated)

• The ts paths-filter in .github/workflows/ci.yml watches pnpm11/** and root tooling but not pnpr/**. feat(pnpr): registry mounts as the only routing model (RFC pnpm/rfcs#13) #12747 changed only pnpr/** (+ a pacquet benchmark), so ts=false and the whole TS test matrix was skipped — even though those JS tests build and run the pnpr binary against config.yaml at runtime.
• The TS CI / Success gate treats skipped deps as a pass, so the required check went green with zero tests run. Post-merge push CI on main uses the same filter, so main stayed green too.

Suggested fixes (AI-generated)

1. CI blind spot (small, do regardless): add pnpr/** to the ts paths-filter so pnpr-only PRs actually run the JS tests that exercise pnpr. This surfaces the regression; it doesn't fix it.
2. Registry-mock behavior (the actual fix): either seed the real packages (is-negative, is-positive, micromatch, lodash, es5-ext, es6-iterator, foo, @zkochan/async-regex-replace, …) as local hosted fixtures with the version sets the tests expect and narrow the local routes to only-seeded names (unseeded scoped names then proxy npmjs) — or reintroduce a supported way to publish overlays on the default target. The former fits the RFC's hermetic intent; the latter is a design call.

Related: #12747, RFC pnpm/rfcs#13, #12767.

_{Written by an agent (GitHub Copilot CLI, claude-opus-4.8).}