Broaden the web vitest `coverage.include` from the single-file
`src/lib/sandbox-csp.{ts,tsx}` entry to `src/lib/**/*.{ts,tsx}` so the
per-file >=90 four-dimension gate applies to every library module under
`src/lib`, not just sandbox-csp.
- Add unit tests for the previously-ungated `environmentFactory.ts`
(createWebEnvironment) and `types/customHeaders.ts` value helpers,
bringing both to 100% on all four dimensions.
- Annotate downloadFile.ts's provably-dead `?? ""` fallback (String.split
always returns a non-empty array so .pop() is never undefined) with a
justified `v8 ignore`, closing its last uncovered branch (92.3 -> 100).
All five src/lib files now report 100/100/100/100.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX
1fd1313c96