Fix sidebar resize limit after window growth

[colonelpanic8]

What Changed

• Recompute the thread sidebar maximum width when the browser or Electron window resizes.
• Add focused coverage showing that the allowed sidebar width grows with the viewport.

Why

The sidebar maximum was calculated only during render from the initial window width. If a restored or resized window became wider without another relevant render, the resize rail retained the old cap and could not use the newly available space.

UI Changes

Behavioral only; there are no visual styling changes. In a controlled browser, a stored 900px sidebar correctly clamped to 360px at a 1000px viewport, then returned to 900px when the viewport grew to 1600px, leaving 700px for main content. The collaborative preview screenshot and recording endpoints timed out, so no media is attached.

Validation

• vp test run --project unit src/components/threadSidebarWidth.test.ts (from apps/web)
• vp fmt --check apps/web/src/components/AppSidebarLayout.tsx apps/web/src/components/threadSidebarWidth.test.ts
• vp lint apps/web/src/components/AppSidebarLayout.tsx apps/web/src/components/threadSidebarWidth.test.ts
• git diff --check
• Web package typecheck attempted; it is currently blocked by unrelated existing errors in BranchToolbarBranchSelector, ModelPickerContent, PreviewAutomationHosts, and state atom hooks.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes (preview capture timed out)
• I included a video for animation/interaction changes (preview recording failed)

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Note

Low Risk
Layout-only sidebar sizing and localStorage width persistence; no auth, data, or API changes.

Overview
Fixes the thread sidebar staying capped at the initial window width after the viewport grows, so drag-resize could not reclaim space even when a wide preference was stored.

AppSidebarLayout now drives --sidebar-width through resolveThreadSidebarCssWidth (a live min/max/calc(100vw …) expression) and passes a maxWidth callback that reads window.innerWidth on each clamp during rail resize. Initial load reads storage with only min/default handling (hydrateStoredWidth: false on the shared Sidebar so hydration stays in the layout).

The shared Sidebar rail gains optional getCssWidth and hydrateStoredWidth, function-valued maxWidth, clamp helpers, commit-time CSS updates via getCssWidth, persisting the clamped width, and onResize(storedWidth) on hydrate so the numeric preference is not lost when the viewport is temporarily narrow. A resize listener briefly disables width transitions to avoid glitches when the CSS clamp adjusts.

^{Reviewed by Cursor Bugbot for commit ea0cea1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix sidebar resize limit to respect window growth after viewport expansion

• The sidebar's maximum width was previously clamped at read time, so growing the window did not increase the allowed resize limit. Now maxWidth is resolved dynamically per-resize via window.innerWidth.
• Adds resolveThreadSidebarCssWidth and resolveSidebarCssWidth helpers that express sidebar width as a CSS min/max expression, so the sidebar clamps live in CSS instead of only at resize commit time.
• Stored width hydration is decoupled: hydrateStoredWidth can be disabled on the Sidebar component, with the caller (AppSidebarLayout) managing its own hydration.
• On window resize, CSS transitions are temporarily suppressed to avoid visual glitches when the sidebar width is adjusted to fit the new viewport.
• Behavioral Change: readInitialThreadSidebarWidth no longer clamps to the viewport at read time; it clamps only to THREAD_SIDEBAR_MIN_WIDTH and falls back to THREAD_SIDEBAR_DEFAULT_WIDTH.

^{Macroscope summarized ea0cea1.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

Bug fix for sidebar resize behavior introduces new runtime event listeners and API options to a shared component. External contributor with no prior commits to this repository (labeled 'vouch:unvouched').

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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