Fix iOS live terminal blank and flashing frames

[azooz2003-bit]

Summary

• serialize ordinary output, local scroll, and verified replay at the tokened Ghostty presentation callback
• keep fallback content visible until the matching frame is presented
• coalesce newest pending work and cover stale callbacks with reducer tests

Verification

• macOS tagged build lvsync succeeded
• iOS simulator build and live scroll/output verification pending cloud capacity

Fixes the takeover regression where scrolling during live agent output could reveal a blank cursor-only surface or flash/reorder rows.

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Summary by cubic

Serialize live terminal frame presentation and harden keyboard dock transitions to eliminate blank/flash frames during live output and preserve animation ordering on iOS.

• Add a tokened TerminalRenderPresentationGate in CmuxMobileTerminal to serialize ordinary, local-scroll, and verified-replay frames. Keep the snapshot fallback visible until the matching tokened frame is presented; cancel failed verified-replay submissions; coalesce renders behind the platform presentation callback.
• Drain pending native scroll and await local-scroll application before verified-replay reveal; re-fence verified-replay restore/scroll in GhosttySurfaceRepresentable.
• Fix keyboard notification races: export beginFrame and beginOverlap in CmuxMobileSupport’s MobileKeyboardTransition; introduce a KeyboardNotificationTransitionLifecycle reducer to ignore stale/duplicate legs, converge after reattach, and settle without restarting animations.
• Replace verified-replay–specific submission path with a unified render submission; resume queued frames after replay suppression; add tests for the presentation gate, keyboard lifecycle, and scroll-drain before reveal.
• CI: build arm64 simulator artifacts in reload workflow.

^{Written for commit a4d3f81. Summary will update on new commits.}

[coderabbitai]

Caution

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-ios-live-output-scroll-render

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