Fix#1647: on Windows/Linux the macOS-only `menlo` default left terminal ASCII garbled on cold start until a manual resize, because the primary glyphs fell through to a bundled `font-display: swap` webfont (JetBrains Mono) that swapped in after xterm measured the cell grid.
- Store the terminal font default as a platform-neutral `auto` sentinel, resolved to a locally-installed font per OS at render (win32→consolas, linux→dejavu-sans-mono, darwin→menlo). Safe to persist/sync; never leaks one OS's font to another.
- Explicitly preload the bundled webfonts the terminal actually renders with and remeasure on every `document.fonts` `loadingdone`, so any late webfont swap (incl. user-chosen) recovers without a manual resize.
Reviewed by local Codex (3 adversarial passes); findings on default persistence/sync and side-panel no-op writes addressed.
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bincxz