fix(preview): isolate keyboard focus during automation and indicate active focus (#647)

[rynfar]

Closes #647

Summary

1. Host webview focus deflection: While an agent is driving automation (controller === "agent"), any focus event received by the host <webview> element immediately blurs the webview and redirects focus to the host composer via dispatchSnapShotComposerFocus(). If the controller transitions to agent while the webview was focused, or transitions back from agent to user, focus is restored to the host composer. The guest page's CDP automation typing/clicking continues unimpeded without physical user keystrokes inadvertently leaking into the guest DOM input.
2. Main process focus restoration: When an automation control action finalizes in Manager.ts, focus is restored to the main window's webContents.
3. Visual focus indicator: Added usePreviewFocus hook and data-preview-focused attribute with a subtle active focus ring (ring-1 ring-inset ring-ring/60) on PreviewView to visually display when the preview holds keyboard focus.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
pylon-marketing	Ignored	Preview	Sep 21, 2026 3:58pm UTC

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	14.0 KiB	14.0 KiB	+5 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	+4 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	+1 B (+0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	−2 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	+3 B (+0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−5 B (−0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.9 KiB	58.9 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: de96f49 · PR result: 99c689c · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 115.6 KiB
• Claude decoded thread snapshot: 116.3 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.