fix(web): model picker no longer jumps at the end of its open animation

[Claudesaul]

Opening the model picker under a scaled popup measured rows too small, then changed the list height when unscaled measurements arrived. Use offset dimensions for LegendList’s initial web measurements in both ESM and CommonJS, matching the unscaled layout space used by its ResizeObserver path.

Maintainer takeover of #19506, preserving @Claudesaul’s implementation and commits. Merged main. This remains one dependency patch concern; the existing item-size cache already rounds measurements, so the earlier fractional-size finding does not apply.

Scope and approval: existing picker animation regression from #15152. The shared web list measurement also affects desktop’s web UI. No native list measurement changes. Maintainer approval and landing remain with the coordinator.

Verification:

• Current-head CI build/typecheck is blocked by an existing main failure: ThreadDetailsPrRows.browser.test.tsx:236 omits required openInShortcutEnabled. The same failure on main. Coordinator follow-up required.

• CI Test Web also reported one visibility failure in the unchanged ComposerBannerStack.browser.test.tsx:97 (8185 passed). This banner path does not render LegendList. The exact CI merge commit 9ca2842455 with the new patch installed passes that suite locally (2/2); main CI also passed it. This appears unrelated to the measurement fix and remains a coordinator CI-retry/isolation follow-up. The CI result is still red; no green result is claimed.

• Independent Opus 5.5 and GPT-6-Sol reviews: two rounds; the unconfirmed rounding concern was disproved by 4096 Chromium measurements and withdrawn. Final round has no code findings.

• Web typecheck, bundle syntax, patch reverse/forward checks and lockfile hash verification pass.

• PR tests: 0 → 0; existing LegendList patch suite: 22 passed; model-picker logic suite: 18 passed. Synthetic DOM size assertions would only restate the implementation.

• Headless Chromium used the actual provider picker, popup and LegendList with the same isolated three-model catalog and 1280×800 viewport. The baseline copy only reverses the measurement fix. During opening, its measured popup layout height is 201px; it jumps to 204px when the scale animation ends (top edge 507px → 504px in the warm capture). The fixed head uses 204px throughout that transition. Settled screenshots alone do not show the transient error; recordings are below.

• Browser samples are sparse under this headless environment; this takeover does not claim a precise frame rate or reproduce the author’s exact top-edge coordinates.

• macOS, Windows, Electron, iOS and Android were not exercised here. The dependency fix is a candidate for upstream contribution; none was submitted.

Before — scaled initial measurement

Before opening recording

After — unscaled initial measurement

After opening recording

Models: Codex GPT-6-Astra (tests), GPT-6.1-Sol (implementation and coordination), GPT-6-Sol and Claude Opus 5.5 (independent review). Harnesses: Codex and Claude through T3 Code.

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Reviewing files that changed from the base of the PR and between b350759 and e778533.

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• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

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• patches/@legendapp__list@3.3.5.patch

📝 Walkthrough

The patch updates keyboard composer inset handling and React Native list inset and end-scroll behavior. It also changes web list measurements, DOM reordering, and temporary scroll-adjustment padding.

Changes: List layout and scrolling

Layer / File(s)	Summary
Inset, scroll maintenance, and web layout adjustments patches/@legendapp__list@3.3.5.patch	The keyboard composer inset hook accepts height adjustment and animation duration. React Native lists support leading and end inset adjustments and update end-scroll maintenance. Web builds use untransformed element dimensions, a shared DOM move helper, and the applied padding value for temporary scroll adjustment.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: 🔵 Low · up to c7c5b

The fix removes the model picker's jump during its open animation. Lists with fractional row heights may now see small rounding differences in their positions. Confirm that this doesn't matter for those lists before merging.

### Architecture Summary

Architecture risk: 🔵 Low · up to c7c5b

The change affects 1 system.

Changed systems: patches

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — patches (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in patches/@legendapp__list@3.3.5.patch: The react.js patch changes the recorded new-file index hash.
• observed — Modified behavior in patches/@legendapp__list@3.3.5.patch: Container layout baselines now use offsetHeight and offsetWidth instead of getBoundingClientRect, avoiding ancestor transforms in the measured dimensions.
• observed — Modified behavior in patches/@legendapp__list@3.3.5.patch: DOM reordering now routes moves before a stable element or to the end through the shared move helper instead of calling insertion methods directly.
• observed — Modified behavior in patches/@legendapp__list@3.3.5.patch: Temporary padding tracking now records the content node’s applied padding value rather than the separately constructed string.

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 clearly identifies the web model picker animation jump that this pull request fixes.
Description check		The description provides the problem, technical change, scope context, approval references, detailed verification results, limitations, and UI evidence. It does not use separate Problem and Change hea…

Full details: Description check

Explanation

The description provides the problem, technical change, scope context, approval references, detailed verification results, limitations, and UI evidence. It does not use separate Problem and Change headings, and it does not link an explicit maintainer approval comment, but the required information is substantially present.

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Actionable comments posted: 1

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Inline comments:
Review comments at @patches/@legendapp__list@3.3.5.patch:
- Line 1482: Update the container measurement used to build rect so it preserves
fractional layout dimensions without being affected by transforms; replace
offsetHeight and offsetWidth with a transform-independent fractional
measurement, such as the element’s ResizeObserver border-box size. Apply the
same change to both measurement sites.

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• patches/@legendapp__list@3.3.5.patch

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[macroscopeapp]

Sorry, I'm unable to act on this request because you do not have permissions within this repository.

[juliusmarminge]

Taking over this one for batch web-misc-02. I will preserve the contributor commits, verify the unscaled measurement fix, and push updates here. Landing stays with the coordinator.

[juliusmarminge]

Current-head CI Build and Typecheck fails because the merge target already has a test fixture missing required openInShortcutEnabled in ThreadDetailsPrRows.browser.test.tsx:236. The identical failure is on main 325a7e2, main CI job. This PR changes only the dependency patch and lockfile; its own web typecheck and focused tests pass. Handing this existing main blocker to the coordinator rather than broadening this takeover. No bot rerun requested.

[juliusmarminge]

CI follow-up at b350759: Test Web had one visibility failure in unchanged ComposerBannerStack.browser.test.tsx:97 (8185 passed). This banner render does not use the changed LegendList measurements. I checked out the exact CI merge commit 9ca2842455 with the new dependency patch installed and ran the banner suite: 2/2 passed. Main CI also passed it. This looks like unrelated browser-test isolation/hover behavior; the root cause is not proven. CI remains red alongside the separately confirmed main typecheck failure. Handing retry/isolation and landing to the coordinator; no bot re-review or watcher restart.