The mobile terminal rendered blank even though the WebSocket was Connected and
the shell prompt had already streamed in. Root cause (reproduced live): on the
mobile fullscreen layout xterm's CharSizeService can measure a 0-width character
cell, so FitAddon.fit() proposes 0 columns/rows and .xterm-screen (plus the WebGL
canvas) collapses to 0x0 — prompt bytes arrive and are written into xterm's row
DOM but paint into a zero-size box. Renderer-independent and mobile-layout-
specific; not fixed by resize/font-size re-fits because prior guards only validate
the container width and font load, never the resulting measured screen/cell width.
Add guardAgainstCollapsedTerminalScreen (app/utils/terminalPreferences.ts) and arm
it from both terminal surfaces (TerminalModal + SessionTerminal) right after their
initial fit. While the container has a width but .xterm-screen does not, it forces
a genuine DOM-strategy remeasure (forceTerminalFontRemeasure) + fit, re-driven by a
ResizeObserver until the screen has a real width. It waits (does not give up) while
the container is not yet measurable, is bounded so it never spins, and is disposed
on every re-init/close path. Recurrence of FN-7620/FN-7686.
- Add isTerminalScreenCollapsed + guardAgainstCollapsedTerminalScreen with tests
- Wire + dispose the guard across all xterm (re)init/close paths in both surfaces
- Add changeset (patch) and a docs/solutions write-up
Note: reproduced via mobile emulation (393px, iPhone UA, forced touch), not a
physical device; the guard is the structural fix — confirm on a real device.
Fusion-Task-Id: FN-7692
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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