fix(yarn-plugin-external-workspaces): support purely-internal externals

[Saadnajmi]

Summary

Two issues prevented @rnx-kit/yarn-plugin-external-workspaces (v0.1.3) from working with externals that exist locally but were never published to npm:

1. getFinderFromJsonConfig reads from a doubly-nested generated.generated

configuration.ts:93-96 reads:

const parsedJson: WorkspaceOutputJson =
  JSON.parse(fs.readFileSync(jsonPath, "utf8"))?.generated || {};
const generated: Partial<WorkspaceOutputGeneratedContent> =
  typeof parsedJson.generated === "object" ? parsedJson.generated : {};

The first line strips one generated layer, then the second line strips another. The README (and the WorkspaceOutputJson type in types.ts) both document the JSON shape as a single layer:

{ "generated": { "version": "1", "repoPath": "...", "workspaces": {...} } }

With that documented shape, parsedJson.generated is undefined, so generated becomes {}, and findPackage always returns null. Externals silently fall through to npm.

Drop the extra ?.generated so the documented shape works as advertised.

2. Resolver chain hard-fails for packages not published to npm

The external: → fallback: → npm: chain (workspace.ts) is wired such that yarn must resolve the npm step before resolution succeeds. The README says:

automatically falling back to npm semver lookups when the local files are not present

— but the design also runs the npm step when the local files are present (for version coalescing). For purely-internal monorepo packages that simply don't exist on npm, the chain throws 404 even though we have a perfectly good local source.

Add a purely-local fast path: when isLocal === true and resolverType === "local", getCandidates short-circuits to a direct external: locator (the fetcher already resolves it via workspace.localPath). getResolutionDependencies returns {} in the same case so yarn doesn't pre-resolve a non-existent chain.

Test plan

Validated against a real Office monorepo workspace consuming three internal externals from a sibling monorepo on disk:

• yarn install completes cleanly (2066 packages installed in ~38s, no 404s)
• node_modules/<internal-package> is a symlink to ../..//`
• dist/index.js (sharedjs's pre-built artifacts) resolves through the symlink
• No npm registry calls for the purely-internal packages

Without these fixes the install fails at:

<internal-package>s@npm:^1.3.1: Package not found
Response Code: 404 (Not Found)

Notes

• No tests in the package today; happy to add a npm-404 + local-present regression test if you'd like.
• The dist/ bundle is gitignored, so the bundled output isn't part of this PR — you'll regenerate at release time.

[Saadnajmi]

Normally Claude adds itself a co-author, but it didn't here. Regardless, marking as draft till I test more.