[Tests] Cover DoctorSuite filesystem assertions

[github-actions]

WHY are these changes introduced?

DoctorSuite is the base class that release-verification suites (ThemeInitTests, ThemePushTests) extend to assert on files produced by CLI commands. Its three filesystem assertions — assertFile, assertNoFile, and assertDirectory — had no test coverage at all, so regressions in path resolution, content matching, or pass/fail polarity would land silently and surface as wrong doctor results rather than a failing build.

The gap was held open by the test file itself: framework.test.ts auto-mocked ../fs.js without ever configuring the mock, which made every filesystem assertion unobservable and effectively untestable.

The seven-day review of Main tests runs (2026-09-28 to 2026-10-05 UTC, 29 runs, 9 failed jobs) found no actionable flake left to fix: all nine failures were version.test.ts subprocess timeouts and a node-package-manager cache assertion, both already fixed on main by #8669, plus one conf-store rate-limit failure on stable/4.8 already fixed by #8705. With no remaining flake, this closes the coverage gap instead.

WHAT is this pull request doing?

Removes the unused vi.mock('../fs.js') and covers the three filesystem assertions against real files in temporary directories:

• assertFile with no pattern, a matching RegExp, a matching string, and a non-matching string
• assertFile on a missing file, confirming it reports file not found and never reads content
• assertFile with an absolute path and a custom message
• assertNoFile and assertDirectory for both the present and absent cases

Each test writes its own fixtures inside inTemporaryDirectory and asserts on the recorded description/passed/actual contract rather than on internal calls, so the assertions stay refactorable. No production code changed, and the existing vi.mock('../system.js') is kept since command execution is out of scope here.

Validation: the suite was sanity-checked by temporarily inverting assertNoFile's passed flag and dropping the isAbsolutePath branch in assertFile — two of the new tests failed, and both pass again once reverted. pnpm vitest run packages/cli-kit/src/public/node/doctor/ passes 25 tests (up from 17), including with --sequence.shuffle, alongside ESLint and tsc --noEmit on cli-kit. Verified locally on Linux / Node 22; the OS and Node matrix is left to CI.

How to manually test your changes?

CI

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add