[codex] Fix preview automation edge cases

[juliusmarminge]

Why

This is a focused follow-up to #3548 based on the final installed-build smoke test.

Two small automation edge cases remained:

• On macOS, preview_press delivered trusted Meta+A keyboard events, but Chromium did not perform the native Select All editing action. Agents could emit the chord while the focused field remained unchanged.
• Opening a preview without an initial URL created the intended idle tab, but the request still waited for a desktop webview readiness condition. Because an empty tab has no navigation to become ready, preview_open could time out even though the tab had been created successfully.

Root cause

Chromium's debugger input API does not infer macOS editing commands from synthetic Meta chords. Those commands must be attached explicitly to the key-down packet.

The preview automation host also treated every open operation as if it needed navigated guest content. URL-less idle sessions only need the tab and panel state; requiring the rendered overlay made their completion depend on unrelated webview initialization.

How

• Add the common macOS editing and navigation command mappings to preview keyboard packets, gated by the injected host platform. This covers Select All, copy/cut/paste, undo/redo, document and line navigation, selection variants, and delete-to-line-start.
• Keep non-macOS key packets unchanged.
• Skip the desktop-overlay wait only when preview_open is opening or reusing an idle tab without a URL. Opens with a URL and tabs with existing content retain the existing readiness wait.
• Add focused packet, manager-layer, and open-readiness regression coverage.

Validation

• vp test apps/desktop/src/preview/PreviewKeyboard.test.ts apps/desktop/src/preview/Manager.test.ts apps/web/src/components/preview/previewAutomationOpenReadiness.test.ts — 27 tests passed
• vp check — passed
• vp run typecheck — all 15 packages passed

Note

Fix preview automation edge cases for macOS key events and overlay wait conditions

• Adds a commands field to PreviewAutomationKeyEvent and populates it with Chromium editing commands when running on macOS hosts, so Meta-chord shortcuts (e.g. Cmd+C) are handled correctly in the preview.
• Reads the host OS platform from Effect context in Manager.ts and passes isMac to makePreviewAutomationKeySequence so platform-specific key sequences are generated correctly.
• Introduces previewAutomationOpenNeedsOverlay in previewAutomationOpenReadiness.ts to conditionally skip waiting for the desktop overlay when opening a preview into an empty tab with no URL.
• Behavioral Change: automation open no longer unconditionally waits for the desktop overlay; it waits only when a URL is provided or the tab already has rendered content.

^{Macroscope summarized 4ba8c96.}

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Note

Low Risk
Targeted preview automation behavior with regression tests; no auth, data, or broad API surface changes.

Overview
Fixes two preview automation edge cases: macOS Meta shortcuts not performing native editing actions, and preview_open timing out on URL-less idle tabs.

On darwin, makePreviewAutomationKeySequence now attaches Chromium CDP commands (select all, copy/cut/paste, undo/redo, line/document navigation, etc.) to synthetic Meta chords; PreviewManager reads HostProcessPlatform and passes isMac into key dispatch. Non-macOS packets are unchanged.

For open, the web automation host only waits for the desktop webview overlay when previewAutomationOpenNeedsOverlay says so—i.e. when a URL is provided or the session is not idle. Reusing or creating an empty idle tab no longer blocks on overlay readiness.

^{Reviewed by Cursor Bugbot for commit 4ba8c96. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[macroscopeapp]

Approvability

Verdict: Approved

Straightforward bug fixes for preview automation edge cases: adds macOS editing command support for Chromium synthetic key events and optimizes overlay waiting logic for empty tabs. Changes are well-tested and self-contained.

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