feat: collapsible sidebar

[basmilius]

What Changed

• Added a sidebar.toggle keybinding command bound to mod+b by default, gated on when: "!terminalFocus" so it stays out of the way inside the terminal drawer.
• Added a matching Toggle sidebar action to the command palette that surfaces the active shortcut hint.
• Lifted SidebarProvider to the root layout so both the palette and the global chat shortcut handler can call useSidebar().toggleSidebar().
• Exposed sidebar open/collapsed state via data-state on the sidebar wrapper so chrome can react with group-data-* classes instead of reading the context everywhere.
• Electron drag-region headers (ChatView, NoActiveThreadState, settings) reserve pl-[90px] when the sidebar is collapsed so the macOS traffic lights don't overlap the active title. Windows/Linux fall through to the existing wco: overrides. The padding transitions at the same duration-200 ease-linear as the sidebar width, so it slides in sync.
• Ran the sidebar toggle on the capture phase because Lexical's core onKeyDown claims mod+b for the bold command and calls preventDefault, which would trip the event.defaultPrevented guard in the shared handler.
• Updated apps/web/src/keybindings.test.ts, apps/server/src/keybindings.test.ts defaults, and KEYBINDINGS.md.

Why

Closes #2282. The thread sidebar was always visible, which made it hard to fully focus on the active chat. A toggle is the smallest useful change that enables focus mode while keeping thread switching (mod+1..9, mod+shift+[/]) available even when the sidebar is collapsed — those listeners live on window in Sidebar.tsx and the sidebar DOM stays mounted under collapsible="offcanvas", so nothing extra was needed to satisfy that requirement from the issue.

Reusing the existing SidebarProvider / useSidebar() / cookie persistence already shipped in ui/sidebar.tsx kept the diff small and means sidebar state still survives reloads.

UI Changes

Video attached showing open → collapsed → open with mod+b, thread switching while collapsed, and the animated header padding on macOS so the traffic lights aren't covered.

Schermopname.2026-04-23.om.12.20.58.mov

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Note

Medium Risk
Moderate risk because it changes global keyboard handling (including capture-phase listeners) and lifts sidebar state to the app root, which could affect shortcut precedence and layout behavior across routes.

Overview
Introduces a new sidebar.toggle keybinding command, registered in contracts/server defaults (bound to mod+b when !terminalFocus) and documented in KEYBINDINGS.md, with corresponding test coverage updates.

Updates the web app to allow toggling the thread sidebar from both the command palette (new “Toggle sidebar” action showing the shortcut) and a global capture-phase keydown handler to avoid editor interception. Sidebar state management is lifted by moving SidebarProvider to the root route, and the sidebar wrapper now exposes data-state so Electron drag-region headers (ChatView, NoActiveThreadState, settings) can adjust left padding/transition when collapsed.

^{Reviewed by Cursor Bugbot for commit 5b49b1e. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add collapsible sidebar with mod+b keybinding and command palette action

• Adds a sidebar.toggle command registered in keybinding contracts, server defaults, and the command palette, mapped to mod+b when not in terminal focus.
• Moves SidebarProvider from AppSidebarLayout to the app root in __root.tsx so sidebar state is accessible across routes.
• Adds a capture-phase keydown listener in _chat.tsx to intercept mod+b before editor handlers (e.g. bold) can consume it.
• Chat header and empty-state header animate left padding in Electron when the sidebar collapses, driven by group-data selectors on the SidebarProvider wrapper.

^{Macroscope summarized 5b49b1e.}

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[cursor]

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

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature (collapsible sidebar with keyboard shortcut) that adds new behavior across multiple components and routes. New features with user-facing behavior changes warrant human review.

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[basmilius]

@juliusmarminge Do I need to authenticate with Vercel or is it something that needs approval?

[Almighty-Shogun]

For someone who doesn't use T3 on fullscreen, this is very usefull!