feat(gui): morph the sidebar collapse instead of swapping renders

The collapse read as a hard cut: only the track width animated while the
panel content swapped instantly and the rail icons bore no relation to the
expanded layout. Now the four control rows persist across the transition —
collapse toggle, new session, new workspace, search, the same top-down
order as their expanded rows — and morph their geometry (row heights,
paddings, margins, capsule borders) on the deepsuite curve, so each rail
icon is its expanded control converging onto the 56px axis. Wide-only
content (brand, labels, input, session tree) cross-fades over 200ms, stays
mounted while the collapse animates, and unmounts at the 300ms settle,
still dropping the sessions subscription. The search query moves up to the
root and survives the round trip; rail search focuses the surviving input
after expand instead of remount-autofocus.

.agents/notes/implemented/bug-fix/2026-07-22-collapsed-sidebar-control-rail.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-22-collapsed-sidebar-control-rail.md: 90039110f4c1e97002fe45ebe42697452b2c6155
-2026-07-22-collapsed-sidebar-control-rail.zh.md: e5cd1c4911bbe02e10d2f1506943024bde862f12
+2026-07-22-collapsed-sidebar-control-rail.md: e959eef37a9e9c0fea79b82ff970daddd9257609
+2026-07-22-collapsed-sidebar-control-rail.zh.md: 7f6d6529a8aa4a655a1d3292e7f41bfb822f05a3

.agents/notes/implemented/bug-fix/2026-07-22-collapsed-sidebar-control-rail.md

@@ -14,7 +14,7 @@ The layout maps a closed sidebar (persisted width `0`) to the fixed `SIDEBAR_COL
 
 `AppFrame` marks the sidebar collapsed from the persisted width preference rather than from the resolved track width, removes the resize handle while collapsed, and passes `collapsed` to the sidebar slot as owner props from the render site. Collapse and expand animate: the frame transitions `grid-template-columns` (and the remaining handle its `left`) on the deepsuite sider curve — `--ds-ease-in-out` over `--ds-transition-duration-slow`, both supplied by ui-theme's base sheet; transitions pause during drags and under `prefers-reduced-motion`.
 
-`SidebarRoot` reads the owner `collapsed` prop. Its collapsed render is the rail: expand toggle, new session, search, and new workspace icons (each aligned with its expanded counterpart's behavior — the search icon expands the sidebar and focuses the search box) plus the `Settings` foot. The brand, capsule button, search field, and session tree leave the rendered and accessibility trees — the body component unmounts, dropping its sessions subscription.
+`SidebarRoot` reads the owner `collapsed` prop and morphs in place rather than swapping renders: the four control rows persist into the rail — expand toggle, new session, new workspace, search, in the same top-down order as their expanded rows — animating their geometry (heights, paddings, margins, capsule borders) on the same curve, each aligned with its expanded counterpart's behavior (the search icon expands the sidebar and focuses the search box). Wide-only content (brand, labels, input, session tree) cross-fades out over 200ms, stays mounted while the collapse animates, and unmounts once the 300ms settle passes — dropping the sessions subscription and leaving the rendered and accessibility trees. The search query lives with the root and survives the round trip.
 
 ## Alternatives considered
 

.agents/notes/implemented/bug-fix/2026-07-22-collapsed-sidebar-control-rail.zh.md

@@ -14,7 +14,7 @@ Status: implemented
 
 `AppFrame` 根据持久化的宽度偏好标记侧边栏是否折叠，而不是根据求解后的轨道宽度来判断；折叠时移除尺寸调整手柄，并在渲染点把 `collapsed` 作为 owner props 传给侧边栏插槽。折叠与展开带动画：frame 对 `grid-template-columns`（以及余下手柄的 `left`）应用 deepsuite 侧栏曲线过渡——`--ds-ease-in-out` 配 `--ds-transition-duration-slow`，两个变量由 ui-theme 的 base 表提供；拖拽期间和 `prefers-reduced-motion` 下过渡暂停。
 
-`SidebarRoot` 读取 owner 的 `collapsed` 属性。折叠渲染即控制栏：展开开关、新建会话、搜索、新建工作区四个图标（行为与展开态对应控件对齐——搜索图标会展开侧边栏并聚焦搜索框），加上底部的 `Settings`。品牌标识、胶囊按钮、搜索框和会话树离开渲染树与可访问性树——主体组件卸载，随之退订会话列表。
+`SidebarRoot` 读取 owner 的 `collapsed` 属性，原地 morph 而非切换渲染：四个控件行持续存在并演变为控制栏——展开开关、新建会话、新建工作区、搜索，自上而下与展开态各行顺序一致——几何（行高、内边距、外边距、胶囊边框）走同一条曲线动画，行为与展开态对应控件对齐（搜索图标会展开侧边栏并聚焦搜索框）。宽态专属内容（品牌标识、文字标签、输入框、会话树）以 200ms 交叉淡出，折叠动画期间保持挂载，300ms settle 后卸载——随之退订会话列表并离开渲染树与可访问性树。搜索关键词由根组件持有，折叠往返后保留。
 
 ## 曾考虑的替代方案