fix(web): right panel opens at half the window on wide screens

[otavio]

The right panel (browser, diff, files, terminal, etc.) always opened at a fixed 540px in a thread that had not been resized yet. On large monitors that is a thin strip, and because widths are remembered per thread (#11310), you had to drag it wider again in every new thread.

The panel now opens at half the viewport width, never smaller than the previous 540px. The existing max-width clamp still reserves room for the chat column, and threads that already have a saved width keep it. The pull-requests page already opened its panel at half the window, so this lines up with that.

Before / after (1920×1080 viewport, this PR's diff open in the panel)

Before: the panel opens at 540px, so diff lines wrap

After: the panel opens at 960px (half the window), so the same diff fits

Verification

• vp test run apps/web/src/components/preview/PreviewPanelShell.test.ts (adds cases for the half-viewport default and the 540px floor)
• vp lint on the touched files, apps/web typecheck
• Checked in a dev build: on a 1920px viewport the inline panel measured 540px before and 960px after

Surfaces: the width only applies to the inline desktop/web panel. The sheet mode on narrow windows and mobile are unchanged.

Made by Claude Opus 5.5 in Claude Code (via T3 Code).

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The production preview panel now uses a viewport-dependent initial width instead of the fixed 540px default, changing the opening layout on wide screens. Existing saved widths and maximum-width constraints remain in place, and targeted tests cover the new calculation.

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📥 Commits

Reviewing files that changed from the base of the PR and between 2a9832b and 1fd75eb.

📒 Files selected for processing (2)

• apps/web/src/components/preview/PreviewPanelShell.test.ts
• apps/web/src/components/preview/PreviewPanelShell.tsx

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📝 Walkthrough

Walkthrough

The preview panel now uses half the viewport width as its default when that value exceeds 540px. The existing maximum-width clamp remains in place. Tests cover a 2,561px viewport and a 1,000px viewport.

Changes

Preview panel width

Layer / File(s)	Summary
Derive and apply the default width apps/web/src/components/preview/PreviewPanelShell.tsx, apps/web/src/components/preview/PreviewPanelShell.test.ts	The exported getPreviewPanelDefaultWidth returns the greater of 540px and half the supplied viewport width. The shell uses window.innerWidth when available, or 0 during server-side rendering, when no defaultWidth override is supplied. Tests expect 1,280px for a 2,561px viewport and 540px for a 1,000px viewport.

Priority: ⬇️ Low

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

Change: Bug fix

Suggested reviewers: bil0000

Merge Risk: ⚪ Minimal · up to 1fd75

The panel’s new default width is consistent with the stated behavior, and no actionable merge-blocking risk is established.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description clearly explains what changed and why. It includes before-and-after UI screenshots, verification steps, and scope details. It does not reproduce the checklist section, but the required…
Title check	✅ Passed	The title is concise and accurately identifies the main change: the right panel now opens at half the window width on wide screens.

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