Follow-up to the first round of review comments:
- Guard `document.fonts` add/removeEventListener with feature detection.
Without the guard, environments where FontFaceSet doesn't expose
EventTarget (jsdom test mocks, older browsers) threw a TypeError
during xterm init and the terminal silently failed to attach.
- Update DirectTerminal.render.test.tsx mock so `document.fonts`
exposes addEventListener/removeEventListener stubs, restoring
happy-path coverage of the init code path.
- Export `resolveMonoFontFamily` and add unit tests covering:
CSS var present (prepended to fallback), CSS var absent
(fallback only), and the invariant that no `var(...)` token ever
leaks into the output.
- Clarify in the docblock why we read `--font-jetbrains-mono` and
deliberately avoid `--font-mono` (the latter re-wraps in `var(...)`
and would re-introduce the bug).
Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>
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