[latekvo]

Replaces #740 (closed as too large). Closes #805, closes #838. Fixes the retry half of #806 (an aborted capture is still reported as a timeout).

Issue: screenshot-diff resampled any pair within 1% of the same aspect ratio to a common size. On live devices this produced false results:

• An unchanged iOS screen diffed at scale 1.0 vs 0.25 reported changed. One resampled pixel was enough to start OCR. OCR then read each file at its own resolution and reported text changes that did not happen.
• Full-resolution captures from different device models (iPhone 16 vs 16 Pro) were compared as one screen.

The live capture also retried silently at the default scale after a failed full-resolution capture.

Fix: compare only images of identical dimensions. Any size difference is a dimension_mismatch, and nothing is compared. The live capture is full resolution only and reports its own error. The emulator refusal behind the retry was fixed in software-mansion/radon#228, which the shipped radon-main sim-server includes.

Same screen, real devices	Before	After
iOS 1.0 baseline vs 0.25	changed, 2 phantom text changes	dimension_mismatch
Android 1.0 baseline vs 0.25	resized_no_change	dimension_mismatch
1.0 baseline + captureCurrent	unchanged	unchanged
1.0 baseline + captureCurrent, text size raised	changed	changed (iOS 8.51%, Android 4.84%)

Prose	Before	After
description	Keep baselines per device model; different aspect ratios fail as a dimension mismatch.	Both images must have identical dimensions: save baselines with screenshot scale: 1.0, one per device model, orientation and foldable posture. Any size difference is reported as a dimension mismatch and nothing is compared.
summary, dimension_mismatch	(no remedy)	only images of identical dimensions are compared; capture both on the same device model, in the same orientation, at the same screenshot scale (live captures use scale: 1.0)
summary, compared result	(no size)	compared_at: WxH
summary	size_normalized block, resized_no_change status	removed

On a foldable simulator, one panel at another scale or orientation no longer gets the posture hint telling the agent to fold the device.

Flow snapshot: steps already key baselines on the exact capture WxH at scale 1.0, so full-screen snapshots never reached the resampling. cropOn already required identical sizes. Docs (features/visual-regression) and the argent-screenshot-diff skill are updated.

Verification

• E2E on an iOS 18.5 simulator (1206x2622) and a Pixel 6 API 34 emulator (1080x2400). The branch's executeScreenshotDiffTool ran in-process with real httpScreenshot captures from the running simulator-servers. The "Before" rows are this PR's base on the same captures.
• Tests: identical-size pairs, scale pairs (10x20 vs 20x40), cross-device pairs (1179x2556 vs 1206x2622, 1080x2424 vs 1080x2400), the no-retry capture path, a width-only pair (1080x2400 vs 1440x2400) and a foldable panel at two scales (no posture hint). Each fails when its rule is mutated (|| -> &&, height or width check dropped, remedy line dropped, same-aspect guard dropped).
• tsc --build, tests typecheck and prettier pass. The full tool-server vitest suite passes in 6 shards; 3 timing tests failed under load and pass in isolation (lens-tools-platform-gate, flow-script-lifecycle).

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• packages/tool-server/src/tools/screenshot-diff/screenshot-diff-summary.ts
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Walkthrough

Screenshot diff descriptions document default-scale fallback for live captures. The summary recommends matching screenshot scales and describes diffPath as the diff image at the compared size. Tests cover the updated descriptions and guidance.

Changes: Screenshot diff scale guidance

Layer / File(s)	Summary
Capture scale descriptions and summary packages/tool-server/src/tools/screenshot-diff/index.ts, packages/tool-server/src/tools/screenshot-diff/screenshot-diff-summary.ts, packages/tool-server/test/screenshot-diff-tool.test.ts	Capture descriptions document default-scale fallback. The summary recommends capturing both images at the same scale and describes diffPath as the compared-size image. Tests check the guidance with an 8×8 baseline and a 4×4 fallback capture.

Priority: Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Possibly related PRs

• software-mansion/argent#740: Documents screenshot capture scale and fallback behavior in the same tool descriptions and summary.

Suggested reviewers: filip131311

Merge Risk: Minimal · up to 515c4

The fallback description matches the supported capture paths, and the summary and test cover the model-and-scale guidance. No concrete merge-blocking risk remains.

Pre-merge checks: 4

Check name	Status	Explanation
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.
Title check		The title describes the screenshot-diff behavior documented by the changes and is related to the PR. However, the changeset primarily updates wording and tests rather than implementing dimension compa…
Description check		The pull request description directly explains the screenshot-diff changes, their motivation, expected behavior, documentation updates, and verification results.

Full details: Title check

Explanation

The title describes the screenshot-diff behavior documented by the changes and is related to the PR. However, the changeset primarily updates wording and tests rather than implementing dimension comparison.

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Inline comments:
Review comments at @packages/tool-server/src/tools/screenshot-diff/index.ts:
- Line 115: Update the screenshot-diff tool description to limit the
default-scale fallback to simulator-server captures; clarify that physical
iPhone captures via captureIosDeviceLiveInput do not retry after a failed
full-resolution capture.

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[latekvo]

[Diplomat, Opus 5.5]: Ran claims-vs-code, nearest-twin, non-happy-path, input, reachability and leak passes on bc2f6a7, plus a mutation pass: each of the 7 changed strings reverted one at a time turns screenshot-diff-tool.test.ts red. Full tool-server vitest (6758 tests), tests typecheck, prettier and eslint pass locally. One low-severity wording gap below.

[latekvo]

Will diff even work properly when not using the full resolution? 99% it will but i prefer to verify this before merging.

[latekvo]

[Diplomat, Opus 5.5]: Partly. Ran it on live devices: same screen captured at scale 1.0 and at the default 0.25 (what the fallback returns), diffed with this branch's diffPngFiles.

Pair (same screen unless noted)	Android Pixel 6 (1080x2400)	iOS 18.5 sim (1206x2622)
1.0 vs 1.0	unchanged, 0 px	unchanged, 0 px
0.25 vs 0.25	unchanged, 0 px	unchanged, 0 px
1.0 baseline vs 0.25 current	resized_no_change, 0 px	changed, 1 px of 198,112, 0 regions, 2 phantom text changes
1.0 baseline vs 0.25 current, text size Large -> Extra Large	-	changed, 10.51%, 9 regions (1.0 vs 1.0: 8.51%, 11 regions)

• The pixel diff works. A real change is caught at 0.25 with similar coverage.
• The OCR text pass does not. It reads each file at its own resolution and only rescales the boxes (fix(screenshot-diff): rescale OCR text bounds into the normalized diff space #442), and tesseract reads a 302 px wide image differently from a 1206 px one. One resampled pixel is enough to trigger OCR, and it then reports Moved/restyled: "Q Search" and Disappeared: "App Store, Apple services and more." for an identical screen. OCR on both sides at the compared size reported 0 text changes for the same pair. At 0.25 the text list is noisy even when both sides are small (Appeared: "nin").
• The summary already warns that differences "may include resampling artifacts" when size_normalized is shown. This PR only documents the fallback and does not change it. The full-res refusal behind the fallback was fixed in radon#210, so the fallback should now be rare. Details added to screenshot-diff: the silent scale fallback can erase a real regression, and the result never says which resolution it compared #805, which tracks what normalization does to the comparison.

[latekvo]

[Diplomat, Opus 5.5]: Reviewed 94e763f (this branch merged with main) using claims-vs-code, nearest-twin, non-happy-path/input, reachability/lifetime and mutation passes. Fixed in f9c98c7:

• Foldable posture hint. A scale-only mismatch on an iPhone Duo (cover panel 350x509 vs 1398x2034) now reaches foldablePostureHint. It named the same panel for both sizes and still said to fold the device. Reproduced through executeScreenshotDiffTool with mocked devicectl panels. After the fix the same run has no posture line.
• Width check untested. Dropping the width half of the dimension check left all 87 screenshot-diff/flow-visual tests green. A 1080x2400 vs 1440x2400 PNG pair then came back unchanged. A width-only case now fails under that mutation.
• Stale prose. The captureIosDeviceLiveInput docstring still mentioned the removed scale fallback, and the skill said any other device model returns dimension_mismatch (same-resolution models are compared).
• PR body. It cited the closed radon#210 (the fix is software-mansion/radon#228, present in all four shipped radon-main binaries) and closed #806, whose cancellation item still stands (an aborted capture reports Screenshot timed out ... may be unresponsive).

Pre-existing doc gaps found on the way: #1569, #1570.

[latekvo]

[Diplomat, Opus 5.5]: Reviewed d38c0f3 (this branch merged with main). I ran one reviewer for each of: claims vs code, nearest twin, non-happy paths/inputs, reachability/lifetime, absence, flows impact and mutations, plus a completeness critic. Live-capture E2E ran on an iOS 18.5 simulator and a Pixel 6 API 34 emulator. Nothing was high or medium. I fixed these four in 1fbfe6c:

• Orientation missing from the remedy. A 60x130 baseline against a 130x60 current got "capture both on the same device model at the same screenshot scale", which both images already met. The remedy and the tool description now name orientation and say live captures use scale 1.0.
• Compared size never stated (#805). Two saved images at the default 0.25 scale gave a summary identical to a full-resolution one. A compared result now prints compared_at: WxH.
• Posture hint on one rotated panel. On the iPhone Duo, 2853x2007 against 2007x2853 still told the agent to fold the device. The hint now skips a transposed pair, the same as a rescaled one.
• False test comment. A flow-visual.test.ts comment said a rotated baseline reaches the dimension-mismatch branch. The snapshot key already includes WxH, so it cannot.

Each fix has a test that fails when the fix is reverted. Tests typecheck, eslint, prettier and knip pass, and the full tool-server suite passes in 6 shards except e2e-tool-aliases, which also fails locally on main. Pre-existing gaps found on the way are filed as #1681 and #1682; the SKILL's 30% claim is already #1570.

[latekvo]

Folded into #1753 as e9ec7e3, to review together with the other capture fixes.