From Copilot's eighth pass of #1962. The no-op guard tested only
`files.length === 0`, which stopped meaning anything once
`SHARED_SOURCE_FILES` was added: `vitest.shared.mts` alone keeps the total
nonzero, so a moved or renamed `core/` would leave the guard deriving
candidates from a near-empty set and passing on skew it exists to catch.
`sourcesWithNoFiles` now requires every configured dir and every named file to
have contributed, and names the ones that didn't. Directory matching is on a
path separator, so a prefix sibling (`core-internal/`) can't vouch for a
renamed `core/`.
Also drops two test comments left stale by the move to `ts.preProcessFile` —
they still described the deleted TRIVIA regex.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HDdo1rNRVQnVRRdsqSrvG3
48d74ba423