[Bug]: workspace-plugin `generate-api` silently skips every export-subpath rollup on Windows

[ArrayKnight]

Area

workspace-plugin (package)

Environment

OS: Windows 11
node v22.12.0
@fluentui/workspace-plugin (in-repo tools/workspace-plugin)

Current Behavior

tools/workspace-plugin/src/executors/generate-api/lib/utils.ts, in getExportSubpathConfigs:

const resolvedPrimaryEntry = resolve(
  configDir,
  primaryMainEntryTemplate.replace(/<unscopedPackageName>/g, unscopedPackageName),
);

const indexDtsSuffix = '/index.d.ts';
if (!resolvedPrimaryEntry.endsWith(indexDtsSuffix)) {
  // …skip
}

path.resolve emits backslash-separated paths on Windows, so resolvedPrimaryEntry never ends
with the hard-coded posix suffix '/index.d.ts'. The guard therefore fires for every project and
every export-subpath API rollup is skipped, silently, on Windows machines. Linux CI is
unaffected, which is why the behaviour has not surfaced there.

Concretely: on a Windows checkout, generate-api for
@fluentui/react-headless-components-preview emits 0 subpath rollups where it should emit 56.
A contributor on Windows therefore cannot regenerate the etc/*.api.md files their change requires,
and — worse — a run that produces nothing looks the same as a run that had nothing to produce.

Expected Behavior

Subpath rollups are generated on every supported development platform, and a path that cannot be
matched raises rather than silently skipping.

Reproduction

On Windows, run generate-api for any package that declares export subpaths (e.g.
@fluentui/react-headless-components-preview) and compare the emitted rollups against a Linux run.

Steps to reproduce

1. On a Windows checkout, run the generate-api executor for a package with exports subpaths.
2. Observe that no per-subpath .d.ts rollup or etc/*.api.md is produced.
3. Instrument resolvedPrimaryEntry — it is backslash-separated and fails the '/index.d.ts' check.

Discovery context

Found while scaffolding a new package with a large export-subpath surface on a Windows checkout,
during work on a styling layer over @fluentui/react-headless-components-preview. The package's
API reports came back empty, and tracing that led here. Nothing about the finding is specific to
that work: any Windows contributor touching a package with subpath exports hits it.

Proposed fix

Normalize to posix separators before the suffix check:

const resolvedPrimaryEntry = resolve(
  configDir,
  primaryMainEntryTemplate.replace(/<unscopedPackageName>/g, unscopedPackageName),
).replace(/\\/g, '/');

One expression, with a comment recording why (so it survives a future tidy). 56 headless rollups
emit locally after the change; CI output is unchanged, since it was already correct there.

A working implementation is included in PR #[WINDMOD-PR-NUMBER] (part of commit d826380ae5);
happy to split it into a standalone PR against this issue — it is independent of everything else in
that PR.

Suggested severity

Medium - Has workaround (regenerate API reports on Linux/WSL or let CI do it).

Products/sites affected

Local development on Windows for any package with export subpaths.

Are you willing to submit a PR to fix?

yes