Lets desktop users collapse the session-list sidebar to maximise the chat
area, without adding any visible UI affordance. Default appearance is
identical to master — only users who actively try to toggle (or know the
keyboard shortcut) ever see a difference.
## Behaviour (desktop only, ≥641px)
| State | Action | Result |
|------------------------------------|-----------------------|-----------------------------------------|
| Sidebar open, click active rail | Toggle | Sidebar collapses to width:0 |
| Sidebar open, click different rail | Normal switch | **Sidebar stays open** (no surprise) |
| Sidebar collapsed, click any rail | Expand + switch | Sidebar expands, then panel switches |
| Anywhere, Cmd/Ctrl+B | Toggle | Same as same-active-rail click |
| Mobile (<641px), any of the above | No-op | Mobile overlay behaviour unchanged |
Two discoverability paths, both opt-in. **No new visible buttons.** Users
who never click the active rail icon see zero UI change vs. master.
## Surface-minimal design
The behaviour is contained behind one extra arg on the rail/sidebar-nav
onclick: `switchPanel('chat',{fromRailClick:true})`. Without that flag the
function preserves master's behaviour exactly — every programmatic
`switchPanel(name)` callsite (commands, deeplinks, internal state changes)
is unaffected. The guard chain inside `switchPanel`:
opts.fromRailClick && _isDesktopWidth() && (
_isSidebarCollapsed() ? expandSidebar() :
prevPanel === nextPanel ? (toggleSidebar(true); return false))
is the ONLY new code path that can cause a collapse. Cross-panel clicks
fall through to the existing switch logic untouched.
## Polish from both source PRs
- **Click-active gesture** as the primary toggle (#1884 @jasonjcwu — the
genuine UX innovation; no extra button needed)
- **Cmd/Ctrl+B keyboard shortcut** (#1924 @spektro33; VS Code convention).
Guarded against firing when typing in INPUT / TEXTAREA / contenteditable
so the shortcut never steals from in-progress text editing.
- **Inline flash-prevention `<script>`** in `<head>` (#1924) sets
`data-sidebar-collapsed='1'` on `<html>` BEFORE the stylesheet loads,
so cold loads with a persisted-collapsed state paint correctly from
frame 0 with no flicker. Cleared by JS once the class system takes over.
- **Smooth slide animation** via `.24s cubic-bezier(.22,1,.36,1)`
(#1924, mirrors the existing workspace-panel collapse on the right)
- **`aria-expanded` mirrored** on the active rail button (#1884) so
screen readers announce open/collapsed transitions.
- **`body.resizing` transition-suppression** (#1884) keeps the drag-resize
cursor instant — no animation during a width-resize gesture.
- **bfcache `pageshow` re-sync** (#1884) — if another tab toggled the
sidebar while this page was frozen, bring it in line on restore.
## Drops vs. #1924
- No persistent rail "toggle sidebar" button (Nathan: keep the UI stealth)
- No close-X button in chat panel head (same reason)
- No i18n keys for the dropped buttons
## What did NOT change
- 22 rail/sidebar-nav `onclick` handlers gained the `{fromRailClick:true}`
arg — function-call shape, invisible to users
- 1 inline `<script>` in `<head>` (flash prevention) — invisible
- 5 lines of CSS — invisible unless someone collapses
That's the entire visible-UI delta. **23 ins / 22 del on `index.html`,
all string-replace.**
## Verification
- 5,151 pytest passing including a new 34-test structural suite covering
every contract (CSS rules, JS functions, fromRailClick guard, legacy
proxy forwarding, flash-prevention `<script>` ordering, mobile
exclusion via :not(.mobile-open) selector, aria-expanded sync).
- Live browser walkthrough at 1280px verified:
- Default boot state identical to master (sidebar open, width 300px)
- Click active rail → collapse (width 1, opacity 0, translateX -14px,
localStorage='1', aria-expanded=false). Panel unchanged.
- Click active rail again → expand back to width 300, aria=true
- Click DIFFERENT rail → normal switch, sidebar stays open (legacy-
preserving case, verified explicitly)
- Click rail while collapsed → expand + switch in one gesture
- Cmd+B toggles correctly
- Cmd+B inside `<textarea>` → suppressed (defaultPrevented=false)
- Reload with collapsed state persisted → restores without flash
- Mobile simulation (matchMedia returns false for min-width:641px):
same-active-rail click is no-op, Cmd+B is no-op, sidebar stays at 300px
Co-authored-by: jasonjcwu <jasonjcwu@users.noreply.github.com>
Co-authored-by: spektro33 <spektro33@users.noreply.github.com>
Closes#1884Closes#1924
2dbee503c2
