fix(desktop): suspend hidden previews, open OAuth popups from the preview

[rynfar]

Two clean cherry-picks from the f94a0d646..bcb855a63 upstream review, plus one security fix found in review.

#8567 — hidden browser previews kept rendering and drained battery. Rendering is now suspended unless the surface is active, has background activity, is picture-in-picture, or is recording.

#8435 — scripted window.open from a preview now opens a real popup instead of navigating the preview away, so OAuth flows complete.

New: popups no longer inherit the preview guest's preload. Upstream's POPUP_WINDOW_OPTIONS overrides contextIsolation, nodeIntegration, and sandbox — but preload is a webPreference too, and an unset one is inherited from the opener. Preview guests load Pylon's pick/annotation preload, which imports ipcRenderer and registers pick, annotation-theme, human-input, and mouse-navigate channels. That was written for the trusted preview surface, not a third-party sign-in page. contextIsolation keeps the page out of the preload's world, so this is defence in depth rather than a live escape.

Two upstream regressions to preview automation, documented not fixed

Both are upstream's design, both survive here, and both affect the preview browser agents drive:

1. preview_status drops viewport for any non-rendering tab. It is the only automation op that does not take the render lease, so readRenderedViewport is skipped and the key is simply omitted (viewport is Schema.optional, so it decodes clean). An agent asking for pixel dimensions on a background tab silently gets nothing and falls back to the CSS setting — wrong on a zoomed or fitted surface.
2. Screenshots can capture a guest that has not painted since resume. captureAutomationSnapshot calls capturePage() with no retry, while startFrameCapture 500 lines earlier retries with a comment naming exactly this failure ("Chromium can return UnknownVizError while a hidden guest is warming its first compositor frame"). Result is a failed preview_snapshot or a 0×0 image returned with no error.

Neither is confirmable without a running Electron build. A follow-up is proposed: the automation path already holds a CDP debugger session (Manager.ts:1162, used for Runtime.evaluate and Accessibility.getFullAXTree), so moving screenshots to Page.captureScreenshot over that same session would decouple them from window visibility entirely.

Verification

Both commits are byte-identical to upstream and Pylon never diverged in the preview subsystem; the one divergence in the touched set, Pylon's persist:pylon-code-preview- partition names, is preserved. Manager.test.ts 66/66 pass. Web browser suites 26/26. Desktop and web typechecks clean. Adversarial review confirmed every acquire has a matching release and that recording and picture-in-picture stay covered by the new lease terms.

Model: Claude Opus 5. Harness: Claude Code.

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[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	13.3 KiB	13.3 KiB	+3 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+4 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−1 B (−0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.5 KiB	55.5 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	13.4 KiB	13.3 KiB	−107 B (−0.8%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−17 B (−0.2%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−90 B (−1.4%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.3 KiB	−88 B (−0.2%)	66.4 KiB	✅
Claude	Live turn messages	11	9	−2 (−18.2%)	21	✅

Baseline: 6a31ea8 · PR result: 1544202 · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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