[Quicksaver]

Summary

Native preview screenshots can return stale pixels or fail when the guest is hidden or minimized, including when the host display is off. A successful capture can therefore show an earlier page state.

Keep the original guest rendering while a bounded isolated-world paint check runs alongside a discarded native warmup capture, then perform the final native readback. Warmup errors allow the final capture to proceed; guest invalidation, interruption and final capture failures still propagate. If paint readiness cannot be confirmed, capture available pixels with freshness unconfirmed.

What changed

• Give each screenshot its own rendering consumer, shared with recording and PiP, and release it after capture.
• Attempt a paint boundary through the existing owned debugger in an isolated world. The outer one-second deadline bounds the caller. Page-side expiry settles the probe and cancels its pending frame when timers run; successful paint clears that timer.
• Discard the concurrent warmup image and save the final native capture. Focused regressions cover retries, final pixel identity, overlapping requests, PiP and recording ownership, cancellation, guest replacement, foreign-debugger fallback, late callbacks and page overrides. Execute the actual probe expression to cover expiry before and between animation frames and timer cleanup on success.

Validation

Focused checks at 1cf3a9e and native proof limits

• At 1cf3a9e103b75eced44174e023902313c9c55d61, vp test run src/preview/Manager.test.ts src/ipc/methods/preview.test.ts from apps/desktop passed all 118 tests. Desktop typecheck, scoped lint and formatting, and git diff --check passed. Two existing Effect suggestions and the constructor-only mock warning remain.
• Web/mobile UI, browser-only screenshots, server/CDP automation, providers and wire contracts are unchanged by this fix. Native measurements below concern the stated source revisions; integrated UI verification and native background-capture measurements were not repeated for this head. Current-head CI and external review results are not yet established.
• Controlled Node VM scheduling verifies paint-expression settlement and callback cleanup. It does not measure native debugger disposal or hidden/display-off behavior. Page timers can pause in a frozen renderer; the outer timeout bounds caller wait only. Fallback mutation freshness remains unconfirmed. Two successful native readbacks remain the normal path cost; persistent failure can consume six bounded attempts. No general performance bound is claimed.
• Retained native comparison used BASE 26285ab80513260d1ff29d2c3fbe18f21990cb62 and AFTER 060e476a8008b69c937082ce2c415d5dc7568837. Windows locked/display-off improved from two of six fresh captures to six of six; Windows unlocked/display-off from one of six to six of six; Mac locked/display-off from four of six to six of six. Saved PNGs were independently decoded, and separate PiP checks retained rendering ownership and restored throttling. These measurements were not rerun at this head. Full React/broker/MCP traversal, native cancellation, live-recording coexistence and system sleep remain unverified.

Proof

Focused validation results and outputs for 1cf3a9e1 · JSON

Retained Windows locked/display-off captures at BASE 26285ab80513260d1ff29d2c3fbe18f21990cb62 and AFTER 060e476a8008b69c937082ce2c415d5dc7568837, not current-head proof. The requested marker was 23757; BASE displays stale marker 15838, while AFTER contains 23757.

Before	After

Independent saved-PNG decoding and hashes · JSON · Native reproduction, state qualification and results · MD

Timing video: before · MP4 · Timing video: after · MP4. These retained recordings illustrate minimized-window behavior at BASE 677d1527 and AFTER 55217a5; they are not current-head proof.

🤖 Generated by GPT 6.1 Sol in Codex via T3 Code.

[macroscopeapp]

Approvability

Verdict: Needs Human Approval

Macroscope's review found this PR not approvable — This targeted fix changes the existing desktop screenshot path to coordinate CDP paint readiness, warmup captures, rendering throttling, and concurrent recording/PiP sessions. Although the focused tests are extensive, the production behavior is sufficiently complex and cross-cutting to warrant human review.

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📝 Walkthrough

Screenshot capture now checks paint readiness through an isolated debugger world, performs a warmup capture, and returns a separately retried final capture. Per-request leases coordinate still-image capture with picture-in-picture and recording.

Changes: Still-image capture

Layer / File(s)	Summary
Paint-aware screenshot capture and lease coordination apps/desktop/src/preview/Manager.ts, apps/desktop/src/preview/Manager.test.ts	Screenshot capture uses a per-request lease, a bounded paint-readiness probe, and separate warmup and final capture attempts. Tests cover retries, overlapping capture consumers, interrupted and stale captures, loading-page scheduling, debugger ownership, throttling restoration, and timed-out probes.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant captureScreenshot
  participant captureStillImage
  participant ControlDebugger
  participant webContents
  captureScreenshot->>captureStillImage: request screenshot
  captureStillImage->>ControlDebugger: probe paint readiness
  captureStillImage->>webContents: capture warmup image
  captureStillImage->>webContents: capture final image
  captureStillImage-->>captureScreenshot: return final image

Loading

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 3b600

Screenshots of background previews now wait briefly for a fresh paint and take a warmup capture before the final image. If readiness cannot be confirmed, the final capture still runs using the pixels that are available. The review found no outstanding source defect, and the one earlier concern about a page check that could stay pending is reported as fixed. On the current revision, native results for hidden or display-off guests have not been re-measured, so a native smoke check before release is advisable. That check does not block merging.

Security architecture risk: 🔵 Low · up to 3b600

The desktop screenshot change preserves existing access boundaries and separates ownership between concurrent captures, recording, and picture-in-picture. No introduced security issue was established. Behavior under a fully suspended renderer or powered-off display remains unconfirmed.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The changed privileged work is scoped to an existing desktop preview guest and its owned control session. Its shared-state impact is rendering ownership within the desktop instance, including coexistence with recording and picture-in-picture; no new cross-service authority is established by this change.

Trust Boundaries and Controls

• observed — The screenshot probe does not attach or displace a foreign debugger. Existing session creation rejects foreign attachment, and native capture checks tab-to-guest identity before and after every attempt. Guest replacement removes the prior control session.

Resilience and Maintainability Implications

• observed — The caller-side paint probe has a one-second deadline. Renderer-side expiry cancels its pending animation frame when timers run, and successful readiness clears the timer. Inspected regressions exercise overlapping owners, interruption, replacement, late completion, and the actual expression in simulated execution worlds; these do not establish native suspended-renderer behavior.

Pre-merge checks: 3 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check		The description clearly explains the problem, implementation, verification results, limitations, and evidence. However, it does not provide the required triaged issue or explicit maintainer approval, …	Add a link to the triaged bug or maintainer approval with the approval comment. If no prior issue or discussion exists, explain why this is an obvious, focused fix that qualifies for the exemption.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: fixing stale pixels in background desktop previews.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description clearly explains the problem, implementation, verification results, limitations, and evidence. However, it does not provide the required triaged issue or explicit maintainer approval, and it does not explain why this focused fix qualifies without them.

Resolution

Add a link to the triaged bug or maintainer approval with the approval comment. If no prior issue or discussion exists, explain why this is an obvious, focused fix that qualifies for the exemption.

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[Quicksaver]

@coderabbitai full review

Following up on #19931 (comment): its latest substantive review still covers 42da166d..711e9689, while the rebased head is feff23bd348c72ecb9c149e283844332c1dc41e9 above 3ff452bd65adf758e68b886d1e3778ae1ec7d970. Please review the complete current PR diff. The rebase preserved the screenshot patch unchanged, and current CI has completed successfully.

Native hidden/display-off behavior has not been rerun at this head. Fallback freshness and disposal of pending native debugger work remain unverified. This request does not satisfy Macroscope's outstanding human approval requirement.

🤖 Generated by GPT 6.1 Sol in Codex via T3 Code.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @apps/desktop/src/preview/Manager.ts:
- Around line 2543-2638: Update the Runtime.evaluate promise in
PreviewManager.probeStillImagePaint to settle even when the guest never runs its
animation frames. Add an in-page timeout that resolves false after the bounded
capture-attempt interval, preserving the existing double-requestAnimationFrame
success path and failure handling.

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[Quicksaver]

@coderabbitai full review

Following up on the screenshot review for 1cf3a9e103b75eced44174e023902313c9c55d61: please verify page-probe expiry, authoritative final capture and independent rendering ownership.

🤖 Generated by GPT 6.1 Sol in Codex via T3 Code.

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[juliusmarminge]

Taking over this one. I'll reduce the capture change and tests to the smallest correct fix, then run independent reviews. Publication will wait for native Electron verification of background freshness and rendering cleanup.

[juliusmarminge]

Takeover rebuilt locally from @Quicksaver's work, but blocked on native Electron verification; no branch changes pushed. Local branch fix/preview-background-screenshots, commit a40886cd3ea261a882798790838b8f2f1e8213a3, base ab6be13d438abeace7617e8d789d59cf2e880f42.

The rebuild reduces the full diff to 211 additions / 5 deletions across Manager and its existing tests. Added tests: 9 → 5; all five fail against main and 116 focused Manager/IPC tests pass. Desktop typecheck, scoped lint and format pass. Fresh independent Claude Opus 5.5 and Codex GPT-6-Sol reviews found no blocking source defect. Warmup/probe/final capture and independent rendering consumers remain; the extra probe wrapper and redundant commentary are removed.

Download the rebuilt patch, test/results, reviews, color/epoch fixture and exact native steps. Run in an isolated checkout of the pinned base with pnpm exec vp run dev:desktop. Start node fixture.mjs, open its page in the native Browser panel, hide that tab, POST /advance, and use desktop-connected preview_snapshot with save:true on its unchanged tabId. Independently verify the new epoch and background color in the saved PNG. Repeat with a minimized window and locked/off display, then overlapping screenshots, recording/PiP, interruption, guest replacement and app close. Verify focus remains unchanged and throttling is restored after the last consumer.

Headless Linux cannot establish these macOS/Windows Electron outcomes. Also measure repeated-capture failure latency (~6.5 s worst case in mocks); no screenshot freshness is guaranteed when the bounded paint probe falls back. That limit is logged, not added to artifact metadata. Publish current-head before/after proof only after native acceptance; original PR/CI still cover the contributor head.

Implementation: Codex GPT-6.1-Sol in T3 Code; tests: Codex GPT-6-Astra.

[Quicksaver]

@juliusmarminge hope this helps move this forward.

Tested your a40886cd3ea2 rebuild against base ab6be13d438a in native Electron on Windows and macOS. It fixes stale or failed screenshots when the app window is hidden or minimized, including overlapping requests, and while the screen is locked (Windows, including with the display turned off; Mac while the display is on). It does not fix a tab hidden behind another tab: capture fails on both builds. preview_snapshot doesn't reach this code at this base.

Proof: evidence archive and interruption receipts

Native before/after results, entry point, lifecycle checks and limits

Applied the supplied rebuild a40886cd3ea261a882798790838b8f2f1e8213a3 unchanged to base ab6be13d438abeace7617e8d789d59cf2e880f42 on both hosts, and ran base and patched apps side by side with isolated state.

Entry point

At this base the patched PreviewManager.captureScreenshot has one caller: the Browser panel's Capture screenshot button, through desktop IPC. preview_snapshot goes through the server's CDP Page.captureScreenshot instead and never reaches this code, so it can't verify the PR. Each capture here calls that same desktop IPC method on the original tab. The button acts on the visible tab of the window being clicked, so the background states below may not be reachable from the UI at this base.

Freshness

Before each request the fixture advances its epoch; independent PNG decoding checks the saved background colour against it, with spot checks of the epoch text. Every capture records the window state just before it. 6 iterations per case, alternating build order; overlap cells count both requests of each pair.

Case	macOS base → rebuild	Windows base → rebuild
Window shown	6/6 → 6/6 current	6/6 → 6/6 current
Shown, overlapping pair	12/12 → 12/12	12/12 → 12/12
Window hidden	2/6 (4 stale) → 6/6	0/6 (all fail) → 6/6
Hidden, overlapping pair	6/12 (6 stale) → 12/12	0/12 (all fail) → 12/12
Window minimized	0/6 (all stale) → 6/6	0/6 (all stale) → 6/6
Minimized, overlapping pair	6/12 → 12/12	6/12 → 12/12
Tab hidden behind another tab	0/18 → 0/18, all fail	0/18 → 0/18, all fail
Screen locked (Mac: display woken behind the lock screen, 3 iterations)	0/9 (all fail) → 9/9	8/18 → 18/18
Screen locked, display turned off	18/18 → 18/18	8/18 → 18/18

Examples from the earlier run: Mac minimized base, requested epoch 11 but saved 10, rebuild, requested/saved 12; Windows minimized base, requested 5 but saved 4, rebuild, requested/saved 6.

Locking behaves differently per OS

• Windows marks both windows hidden within 1.5 seconds of a real lock. Captured every second for 35 seconds, base returned the previous frame in 34 of 35 captures after that point; the rebuild was current in all 40.
• macOS keeps windows visible after a lock. With the display asleep, both builds stayed current for the whole 33-second sampling. Woken behind the lock screen, base capture failed every time while the rebuild was current.
• The test windows were kept on top before locking. A window covered by another app is already hidden, which is the hidden case above.

Failure bounds

A failing base capture returns in about 3.3 seconds; a failing rebuild capture in about 6.5 seconds (the hidden-tab case), matching your ~6.5 s estimate from mocks.

Interruption during warmup and final capture

The app's own GPU process was suspended so native capture attempts stayed pending, and a real captureScreenshot was interrupted 300 ms into the warmup attempt or into the final capture (after three failed warmup attempts). No CDP virtual time was used. 3 runs per stage on each OS:

Check	macOS	Windows
Settled after the interrupt	2–3 ms	0–1 ms
Guest throttling: before → pending → after interrupt (GPU still suspended)	on → off → on	on → off → on
Artifact from the interrupted request	None	None
Window focus and activation	Stayed unfocused; no focus, show or restore events	Same
Next capture after resuming the GPU	6/6 current, paint confirmed, 48–66 ms	6/6 current, paint confirmed, 46–59 ms

Lifecycle checks (earlier run on the same rebuild, vp run dev:desktop on both hosts, receipts re-audited)

Case	macOS	Windows
Interrupt pending capture after the paint probe started	Settled in 3 ms	Settled in 10 ms
Two real capture failures with the app's GPU process suspended	6.494 and 6.491 seconds	6.541 and 6.571 seconds
Destroy guest during capture	Rejected in 19 ms	Rejected in 22 ms
Replacement guest capture	Succeeded, paint confirmed, 90 ms	Succeeded, paint confirmed, 118 ms
Quit app during capture	Rejected in 36 ms; app exited	Rejected in 51 ms; app exited

To hold the probe pending, that harness paused the guest with CDP virtual time and then set it to advance, which fast-forwards timers instead of restoring real time. Every later probe on that guest returned unconfirmed immediately, so the captures after the interruption and after GPU resume took the fallback path: they show no hang, not a confirmed-fresh capture. The GPU-suspension timings ran on that guest too; the probe runs alongside the warmup capture, so the bound shouldn't change, and the re-run above measured the same ~6.5 seconds with a normal clock. Destroy, replacement and quit used a fresh guest. The interruption runs above replace that recovery evidence with a normal clock. The Mac replacement was observed after a 30-second window, so it doesn't establish fast replacement.

Recording awaited the real MediaRecorder start, stayed active across a current still capture, and saved an MP4 on stop; PiP was tested separately with a current capture. In both, base was already current, so they show no regression rather than a fix. Throttling returned to its prior state after consumers stopped.

With animation frames stalled, fallback returned available pixels in about 1.1 seconds. Missing or foreign debugger cases also fell back, with stale pixels observed, and the foreign debugger stayed attached. This proves bounded fallback, not freshness when paint readiness is unconfirmed.

Runtime: Electron 44.4.5, Chromium 152.0.7977.130, on Windows 11 Home 10.0.26200 and macOS 27.0.1 (Apple M1 Pro).

🤖 Generated by GPT 6.1 Sol in Codex and Claude Opus 5.5 in Claude Code via T3 Code.

[juliusmarminge]

Reverting this in #22222 together with the other desktop fixes the takeover campaign merged yesterday. Nothing was wrong with the review of this change; it was merged on CI and code audits only, and after #20907 from the same batch broke existing installs the maintainer decided that desktop changes do not ship without being run on a real desktop build. To bring it back: open a fresh PR from the original commit, run it on a real build that already has user state on each platform it touches, and put the before/after proof in the body.