fix(sidebar): suppress collapse->expand transition flash on fresh load

[waleedlatif1]

Summary

• Opening a fresh tab into the workspace played a sidebar collapse → expand animation on load
• The pre-paint script already sets the correct --sidebar-width, but store rehydration re-applies it a tick later during hydration, and the always-on width/slide transitions animate that re-apply — reading as a collapse → expand flash
• Suppress sidebar transitions during the boot/hydration window via a new html.sidebar-booting class (mirrors the existing html.sidebar-resizing pattern), lifted after the first paint via double-requestAnimationFrame
• User-driven collapse toggles and the fullscreen slide still animate normally; the guard doesn't re-run on soft navigation and cleans up its rAFs/class on unmount

Type of Change

• Bug fix

Testing

Tested manually — fresh load no longer flashes the rail; collapse toggle and fullscreen slide still animate.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Jul 1, 2026 1:09am

[cursor]

PR Summary

Low Risk
UI-only timing/CSS guard around first paint; no auth, data, or API changes.

Overview
Fixes a sidebar collapse → expand flash on a fresh workspace load when persisted width is re-applied during Zustand rehydration a tick after the pre-paint script already set --sidebar-width.

Adds an html.sidebar-booting guard in globals.css (same idea as html.sidebar-resizing) that disables width/transform transitions on the sidebar container and chrome shells during that window. WorkspaceChrome toggles the class in a mount-only useLayoutEffect before persist.rehydrate(), then clears it after a double requestAnimationFrame so normal collapse toggles and fullscreen slide animations still run afterward; cleanup cancels pending rAFs and removes the class on unmount.

^{Reviewed by Cursor Bugbot for commit 54bdb1d. Configure here.}

[greptile-apps]

Greptile Summary

This PR suppresses the fresh-load sidebar transition flash. The main changes are:

• Adds a sidebar-booting global class that disables sidebar transitions during hydration.
• Applies the class from WorkspaceChrome before sidebar store rehydration.
• Removes the class after the first paint with nested animation-frame callbacks.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
apps/sim/app/_styles/globals.css	Adds transition suppression for the sidebar elements while the root has sidebar-booting.
apps/sim/app/workspace/[workspaceId]/components/workspace-chrome/workspace-chrome.tsx	Adds the hydration boot guard lifecycle and imports useRef for animation-frame cleanup.

_{Reviews (1): Last reviewed commit: "chore(sidebar): convert boot-guard comme..." | Re-trigger Greptile}