feat(ui-workspace): flatten session fork rows

packages/client/ui-workspace/README.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 packages/client/ui-workspace/README.md
-README.md: f0dbd3de4ac5b7934b4077b2986f5def5be329c8
-README.zh.md: b9f068c6d1709f0a01d22c3fb1cdc391764d666b
+README.md: 2a4e544250756db50b19bc101c19ac79505a3d6c
+README.zh.md: 7ae2b0e196a98d1375e9073146bb8119ea8cbe90

packages/client/ui-workspace/README.md

@@ -6,7 +6,7 @@ Shared Workspace picker plugin. `WorkspaceBrowser` is registered into the sideba
 
 The picker lists real Host Workspace entities through the global `useWorkspaces` hook. Selecting a Workspace invokes the slot owner's `onPick` callback to retarget the frontend Session object. Each registration declares a **directory-flow child hole** (`single` kind: `conversation.hero.workspace.directoryFlow` / `sidebar.workspaces.directoryFlow`) that the composed picker package's client half fills with its picking interaction — the [`-native`](../../host/directory-picker-native/README.md) backend's renderless OS-chooser driver today, an in-app browsing dialog under a `-browse` composition. The flat **Open local folder...** action renders only while the surface's hole is occupied (occupancy read per menu render; an empty hole means the composition has no picking affordance — the seam's documented no-flow default). This package owns the trigger and the adoption: the occupant reports one picked path per open through the hole's owner conversation (`open`/`busy`/`onPicked`/`onCancel`/`onError`), and the owner adopts it through the object layer, selecting the committed Workspace only after its list projection has refreshed; cancellation is silent, and errors land in the retryable folder dialog whose **Choose again** reopens the flow. **Create a new workspace** retains the name dialog and disables names already present in that list, while the Host remains authoritative for concurrent or non-UI callers. The runtime Session and Workspace services own materialization. The Workspace row's Delete action opens a confirmation that states the retention boundary, blocks duplicate submission, and keeps failures open; success removes the group while its Sessions remain under Ungrouped. The Session row's Rename action opens the same browser-owned dialog pattern prefilled with the row's display title: no client-side conflict rule exists (the host normalizes and may reject with `title-invalid`, rendered in the dialog alert), and confirming an unchanged title is deliberately allowed — it pins the current automatic title against regeneration.
 
-The Session row's Fork action forks at the source's last completed turn and opens the child; the lineage-aware tree nests it beneath the source. A failure leaves the current selection unchanged.
+The Session row's Fork action forks at the source's last completed turn and opens the child; the source and child always appear as peer rows within a workspace group, with lineage retained only as session data. A failure leaves the current selection unchanged.
 
 Both target slots are declared by other plugins, so `apply` registers through declaration-aware deferral and re-registers after a declaring slot is restored.
 

packages/client/ui-workspace/README.zh.md

@@ -6,7 +6,7 @@
 
 该选择器通过全局 `useWorkspaces` hook 列出真实的 Host Workspace 实体。选择 Workspace 会调用 slot owner 的 `onPick` 回调，重新定位前端 Session 对象。每个注册各自声明一个**目录流子洞**（`single` kind：`conversation.hero.workspace.directoryFlow`／`sidebar.workspaces.directoryFlow`），由组合的选择器包 client half 填入其选取交互——今天是 [`-native`](../../host/directory-picker-native/README.md) 后端的无渲染 OS 选择器驱动，`-browse` 组合下则是应用内浏览对话框。平铺显示的 **打开本地文件夹…** 操作仅在本表层的洞被占用时渲染（每次菜单渲染读取占用状态；洞为空意味着该组合没有选目录能力——seam 文档化的无流程默认行为）。本包持有触发与接纳：占用者经洞的 owner 会话（`open`/`busy`/`onPicked`/`onCancel`/`onError`）每次打开上报一个所选路径，owner 通过对象层接纳它，并等待 Workspace 列表投影刷新后才选中已提交的 Workspace；取消操作不会显示提示，错误落入可重试的文件夹对话框，其 **重新选择** 会重新打开流程。**创建新工作区** 操作保留名称对话框，并禁用列表中已有的名称，而 Host 对并发或非 UI 调用方仍具有最终决定权。运行时 Session 与 Workspace 服务负责物化。Workspace 行内的 Delete 操作会打开确认框，说明保留边界、阻止重复提交，并在失败时保持打开；成功后，该分组会被移除，其 Session 则留在 Ungrouped 下。Session 行内的 Rename 操作打开同款浏览器持有的对话框，并以该行的显示标题预填：客户端不设名称冲突规则（host 负责规范化，可能以 `title-invalid` 拒绝，错误渲染在对话框告警区）；确认未修改的标题是有意允许的——这正是把当前自动标题钉住、不再被重新生成覆盖的手势。
 
-Session 行内的 Fork 操作在源会话最后一个已完成轮次处 fork 并打开子会话；感知谱系的树会将子会话嵌套在源会话下。失败不会改变当前选中项。
+Session 行内的 Fork 操作在源会话最后一个已完成轮次处 fork 并打开子会话；源会话与子会话在 workspace 组内始终作为同级行展示，谱系只保留为 session 数据。失败不会改变当前选中项。
 
 两个目标 slot 都由其他插件声明，因此 `apply` 通过声明感知的延迟机制完成注册，并在声明该 slot 的插件恢复后重新注册。
 

packages/client/ui-workspace/src/client/WorkspaceBrowser.tsx

@@ -104,7 +104,6 @@ function SessionTree({
   const list = useSessions(s => s)
   const current = list.current
   const [expandedProjects, setExpandedProjects] = useState<string[]>([])
-  const [expandedSessions, setExpandedSessions] = useState<string[]>([])
   // Transient drag viewing state (never store-bound; order truth stays Host-side).
   const [drag, setDrag] = useState<DragState | null>(null)
   const currentGroup = current === undefined
@@ -115,27 +114,9 @@ function SessionTree({
     if (current === undefined || currentGroup === undefined) return
     setExpandedProjects(l => (l.includes(currentGroup) ? l : [...l, currentGroup]))
   }, [current, currentGroup])
-  // The selected session must be visible: unfold its ancestor chain (fork
-  // lands the child under a possibly folded parent row).
-  const currentAncestors = useMemo(() => {
-    const chain: string[] = []
-    let cursor = current === undefined ? undefined : list.byId[current]?.parentId
-    while (cursor !== undefined && !chain.includes(cursor)) {
-      chain.push(cursor)
-      cursor = list.byId[cursor]?.parentId
-    }
-    return chain
-  }, [current, list])
-  useEffect(() => {
-    if (currentAncestors.length === 0) return
-    setExpandedSessions((l) => {
-      const missing = currentAncestors.filter(id => !l.includes(id))
-      return missing.length === 0 ? l : [...l, ...missing]
-    })
-  }, [currentAncestors])
   const groups = useMemo(
-    () => deriveGroups(list, workspaces, { expandedProjects, expandedSessions, query }),
-    [list, workspaces, expandedProjects, expandedSessions, query],
+    () => deriveGroups(list, workspaces, { expandedProjects, query }),
+    [list, workspaces, expandedProjects, query],
   )
   const now = Date.now()
 
@@ -146,7 +127,7 @@ function SessionTree({
           <div className={css.empty}>{query === '' ? 'No sessions yet' : 'No matches'}</div>
         )}
         {groups.map(group => (
-          // Group section: header row + expanded session subtree. The
+          // Group section: header row + expanded top-level session rows. The
           // inter-group breathing room (former flat-list batch separator)
           // is the section's own margin (WorkspaceBrowser.module.css).
           <div key={group.key} className={css.groupSection}>
@@ -170,7 +151,7 @@ function SessionTree({
                 }}
             />
             {group.sessions.map((node, index) => {
-              // Draggable: real-workspace group roots outside search. The drag
+              // Draggable: real-workspace session rows outside search. The drag
               // never leaves its group — rows of other groups show no markers
               // and reject drops (visual movement confined to this section).
               const draggable = group.workspaceId !== undefined && query === ''
@@ -188,15 +169,15 @@ function SessionTree({
                 drop: (half: 'before' | 'after') => {
                   /* v8 ignore next -- narrowing guard: Rows gates drop on `active`, which is false while the drag state is null. */
                   if (drag === null) return
-                  const roots = group.sessions
+                  const sessions = group.sessions
                   // Anchor = the row the insert line points at ('after' means
                   // the next root; end-of-list omits the anchor → append).
-                  const anchor = half === 'before' ? node.id : roots[index + 1]?.id
+                  const anchor = half === 'before' ? node.id : sessions[index + 1]?.id
                   setDrag(null)
                   if (anchor === drag.sessionId) return
                   // No-op when the drop lands back on the source position.
-                  const sourceIndex = roots.findIndex(r => r.id === drag.sessionId)
-                  const anchorIndex = anchor === undefined ? roots.length : roots.findIndex(r => r.id === anchor)
+                  const sourceIndex = sessions.findIndex(r => r.id === drag.sessionId)
+                  const anchorIndex = anchor === undefined ? sessions.length : sessions.findIndex(r => r.id === anchor)
                   if (sourceIndex !== -1 && (anchorIndex === sourceIndex || anchorIndex === sourceIndex + 1)) return
                   insertSessionBefore(drag.workspaceId, drag.sessionId, anchor).catch((reason: unknown) => {
                     console.warn('session reorder rejected:', reason)
@@ -208,13 +189,11 @@ function SessionTree({
                 <SessionNodeItem
                   key={node.id}
                   node={node}
-                  depth={0}
                   currentId={current}
                   now={now}
                   onOpen={open}
                   onRename={onSessionRename}
                   onFork={forkSession}
-                  onToggle={(id) => { setExpandedSessions(l => toggled(l, id)) }}
                   drag={dragProps}
                 />
               )
@@ -242,15 +221,11 @@ function FlatList({ useSessions, open, forkSession, onSessionRename, query }: Pi
           <SessionNodeItem
             key={node.id}
             node={node}
-            depth={0}
             currentId={list.current}
             now={now}
             onOpen={open}
             onRename={onSessionRename}
             onFork={forkSession}
-            /* v8 ignore next -- required-prop filler: flat rows render no twist, so it never fires. */
-            onToggle={() => {}}
-            flat
           />
         ))}
       </div>

packages/client/ui-workspace/src/client/rows/Rows.module.css

@@ -39,9 +39,7 @@
   height: 20px;
 }
 
-/* Session cell (figma): pad 8, adjacent 16px twist + status slots, then a 4px
-   gap to the title — the slots butt together, so the row gap is zeroed and
-   the title carries its own margins. */
+/* Session cell (figma): pad 8, a 16px status slot, then a 4px title gap. */
 .sessionRow {
   height: 34px;
   gap: 0;
@@ -168,7 +166,7 @@
   background: var(--dsw-alias-interactive-bg-hover);
 }
 
-/* Drag reorder insert line (workspace-group roots): 2px accent above or
+/* Drag reorder insert line (workspace-group session rows): 2px accent above or
    below the hovered row, drawn with box-shadow so no layout shift. */
 .sessionRow.dropBefore {
   box-shadow: 0 -2px 0 0 var(--dsw-alias-state-business-primary);
@@ -233,33 +231,9 @@
   color: var(--dsw-alias-label-primary);
 }
 
-/* Session expand twist occupies the leading 16px slot; keep a spacer when absent
-   so titles align across sibling rows. Duplicates the .iconButton reset instead
-   of `composes:` — the tsdown CSS-modules pipeline drops composes mappings, which
-   left the raw UA button box showing. */
-.twist {
-  flex: none;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 16px;
-  height: 20px;
-  border: none;
-  border-radius: 4px;
-  padding: 0;
-  background: transparent;
-  cursor: pointer;
-}
-
-.twist:hover {
-  color: var(--dsw-alias-label-primary);
-}
-
-/* Chevrons and tree twists ride the caption grey (#ADB2B8); the folder glyph
-   stays one step darker (tertiary, #81858C) per the cell spec. Declared last
-   to win over the composed .iconButton color. */
-.chevron,
-.twist {
+/* Chevrons ride the caption grey (#ADB2B8); the folder glyph stays one step
+   darker (tertiary, #81858C) per the cell spec. */
+.chevron {
   color: var(--dsw-alias-label-caption);
 }
 

packages/client/ui-workspace/src/client/rows/Rows.tsx

@@ -16,9 +16,6 @@ import type { GroupNode, SessionNode } from '../tree.ts'
 import { formatRelativeTime } from '../tree.ts'
 import css from './Rows.module.css'
 
-/** Indent step per tree level: one 16px slot (figma session cell). */
-const INDENT_STEP = 16
-
 const SESSION_MENU_ITEMS = [
   { id: 'rename', label: 'Rename', icon: <IconEditOutline16 /> },
   { id: 'fork', label: 'Fork session', icon: <IconBranchOutline16 /> },
@@ -135,16 +132,12 @@ export function ProjectRowItem({ group, onToggle, onCreate, actions }: {
 }
 
 /**
- * One session subtree: the node's own 34px row (indent by depth, expand
- * twist when it has children, running dot, relative time) plus its visible
- * children, recursively — the component tree mirrors the derived tree.
+ * One top-level 34px session row with running dot and relative time.
  * @param props.node - derived session node.
- * @param props.depth - 0 = directly under the group header.
  * @param props.currentId - selected session id (row highlight).
  * @param props.now - epoch ms for relative-time formatting.
  * @param props.onOpen - open a session by id.
- * @param props.onToggle - unfold/fold a subtree by id.
- * @returns the node's row followed by its children.
+ * @returns the session row.
  */
 /** Hover-card body: full title, relative time, and the status line (running/idle until wire status lands). */
 function SessionHoverContent({ node, now }: { node: SessionNode; now: number }) {
@@ -161,7 +154,7 @@ function SessionHoverContent({ node, now }: { node: SessionNode; now: number })
 }
 
 /**
- * Root-row drag wiring supplied by the group owner (workspace groups only).
+ * Session-row drag wiring supplied by the group owner (workspace groups only).
  * `drop` reports the half of the row the pointer released on: 'before'
  * inserts above this row, 'after' below it (the owner resolves the anchor).
  */
@@ -184,9 +177,8 @@ function rowHalf(e: { clientY: number; currentTarget: HTMLElement }): 'before' |
   return e.clientY < rect.top + rect.height / 2 ? 'before' : 'after'
 }
 
-export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename, onFork, onToggle, drag, flat = false }: {
+export function SessionNodeItem({ node, currentId, now, onOpen, onRename, onFork, drag }: {
   node: SessionNode
-  depth: number
   currentId: string | undefined
   now: number
   onOpen: (id: SessionNode['id']) => void
@@ -194,18 +186,13 @@ export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename,
   onRename: (id: SessionNode['id'], currentTitle: string) => void
   /** Fork a session at its last completed turn (row menu action). */
   onFork: (id: SessionNode['id']) => void
-  onToggle: (id: SessionNode['id']) => void
-  /** Present only on draggable rows (workspace-group roots outside search). */
+  /** Present only on draggable rows (workspace-group sessions outside search). */
   drag?: RowDragProps | undefined
-  /** Flat-list variant: no twist slot (figma flat cell) — titles align on the status slot. */
-  flat?: boolean
 }) {
   const row = node
   const selected = node.id === currentId
   const [menuOpen, setMenuOpen] = useState(false)
-  // Rail (figma session cell: pad 8, twist slot 16, status slot 16, gap 4 to
-  // the title): both slots are always reserved so titles align whether or not
-  // the twist/dot is lit. Extra depth rides the left padding.
+  // Figma session cell: pad 8, status slot 16, then a 4px title gap.
   const ownRow = (
     <div
       className={clsx(
@@ -214,8 +201,6 @@ export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename,
       )}
       role="treeitem"
       aria-selected={selected}
-      {...(row.hasChildren ? { 'aria-expanded': row.expanded } : {})}
-      style={{ paddingLeft: 8 + depth * INDENT_STEP }}
       onClick={() => { onOpen(node.id) }}
       draggable={drag !== undefined}
       onDragStart={drag === undefined
@@ -241,18 +226,6 @@ export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename,
           drag.drop(rowHalf(e))
         }}
     >
-      {row.hasChildren && !flat
-        ? (
-          <button
-            type="button"
-            className={css.twist}
-            aria-label={row.expanded ? 'Collapse' : 'Expand'}
-            onClick={(e) => { e.stopPropagation(); onToggle(node.id) }}
-          >
-            <IconTriangleRightFill14 className={clsx(css.arrow, row.expanded && css.arrowOpen)} />
-          </button>
-        )
-        : null}
       <span className={css.slot}>{row.running && <StateDot state="ongoing" />}</span>
       <span className={css.title}>{row.title}</span>
       <span className={css.time}>{formatRelativeTime(row.updatedAt, now)}</span>
@@ -283,25 +256,10 @@ export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename,
     </div>
   )
   return (
-    <>
-      <HoverCard
-        anchor={ownRow}
-        content={<SessionHoverContent node={node} now={now} />}
-        disabled={menuOpen || drag?.active === true}
-      />
-      {node.children.map(child => (
-        <SessionNodeItem
-          key={child.id}
-          node={child}
-          depth={depth + 1}
-          currentId={currentId}
-          now={now}
-          onOpen={onOpen}
-          onRename={onRename}
-          onFork={onFork}
-          onToggle={onToggle}
-        />
-      ))}
-    </>
+    <HoverCard
+      anchor={ownRow}
+      content={<SessionHoverContent node={node} now={now} />}
+      disabled={menuOpen || drag?.active === true}
+    />
   )
 }

packages/client/ui-workspace/src/client/tree.ts

@@ -11,20 +11,15 @@ export const UNGROUPED_KEY = ''
 /** Display label for the ungrouped bucket row. */
 export const UNGROUPED_LABEL = 'Ungrouped'
 
-/** One session node of a group's visible tree (34px row; children render indented one step). */
+/** One top-level session row in a group or the flat list. */
 export interface SessionNode {
   id: SessionId
   title: string
-  /** Visible children, already expansion/search-filtered (empty when folded). */
-  children: readonly SessionNode[]
-  /** The session HAS children in the data (the twist renders even while folded). */
-  hasChildren: boolean
-  expanded: boolean
   running: boolean
   updatedAt: number
 }
 
-/** One workspace group section: header row facts + the visible session tree. */
+/** One workspace group section: header row facts + visible top-level session rows. */
 export interface GroupNode {
   /** Group key: the workspace id or {@link UNGROUPED_KEY}. */
   key: string
@@ -39,14 +34,13 @@ export interface GroupNode {
   expanded: boolean
   /** The group contains the selected session (active folder tint; supplied here so the renderer never scans). */
   containsCurrent: boolean
-  /** Visible roots (empty while the group is folded). */
+  /** Visible session rows (empty while the group is folded). */
   sessions: readonly SessionNode[]
 }
 
-/** Viewing state consumed by the derivation — the component's local useState arrays, taken as-is. */
+/** Viewing state consumed by the derivation. */
 export interface TreeView {
   expandedProjects: readonly string[]
-  expandedSessions: readonly string[]
   query: string
 }
 
@@ -56,9 +50,7 @@ interface Group {
   cwd: string | undefined
   createdAt: number | undefined
   label: string
-  summaries: Map<SessionId, SessionSummary>
-  roots: SessionId[]
-  children: Map<SessionId, SessionId[]>
+  sessions: SessionSummary[]
 }
 
 /**
@@ -89,7 +81,7 @@ function sessionTitle(session: SessionSummary): string {
   return session.blank ? 'New Session' : session.displayTitle
 }
 
-/** Build one group's parent/child tree from an ordered member list. */
+/** Build one group without projecting session lineage into presentation. */
 function buildGroup(
   key: string,
   workspaceId: WorkspaceId | undefined,
@@ -99,54 +91,11 @@ function buildGroup(
   members: readonly SessionSummary[],
   order: 'account' | 'recency',
 ): Group {
-  const summaries = new Map(members.map(m => [m.id, m]))
-  const children = new Map<SessionId, SessionId[]>()
-  const roots: SessionSummary[] = []
-  for (const m of members) {
-    // A session is a tree child only when its parent lives in the same
-    // group; cross-group or unknown parents degrade to group roots.
-    if (m.parentId !== undefined && m.parentId !== m.id && summaries.has(m.parentId)) {
-      const kids = children.get(m.parentId)
-      if (kids === undefined) children.set(m.parentId, [m.id])
-      else kids.push(m.id)
-    } else {
-      roots.push(m)
-    }
-  }
-  // Workspace order is the member iteration order (workspace.sessionIds), so
-  // attached groups keep insertion order; Ungrouped sorts by recency.
-  if (order === 'recency') {
-    roots.sort(byRecency)
-    for (const kids of children.values()) {
-      kids.sort((a, b) => {
-        const sa = summaries.get(a)
-        const sb = summaries.get(b)
-        /* v8 ignore next -- unreachable: kid ids are inserted alongside their summaries. */
-        if (sa === undefined || sb === undefined) return 0
-        return byRecency(sa, sb)
-      })
-    }
-  }
-  const rootIds = roots.map(r => r.id)
-  // parentId cycles (host bug) leave members unreachable from any root;
-  // surface them as extra roots — the flatten walk's visited set stops
-  // loops. Each node sits in at most one kids list and roots have no
-  // in-group parent, so the scan pushes every reachable node exactly once.
-  const reachable = new Set<SessionId>(rootIds)
-  const stack = [...rootIds]
-  while (stack.length > 0) {
-    const top = stack.pop()
-    /* v8 ignore next -- unreachable: the loop condition guarantees a non-empty stack. */
-    if (top === undefined) break
-    for (const kid of children.get(top) ?? []) {
-      reachable.add(kid)
-      stack.push(kid)
-    }
-  }
-  for (const m of members) {
-    if (!reachable.has(m.id)) rootIds.push(m.id)
-  }
-  return { key, workspaceId, cwd, createdAt, label, summaries, roots: rootIds, children }
+  const sessions = [...members]
+  // Workspace order is workspace.sessionIds; only Ungrouped lacks an account
+  // order and therefore falls back to recency.
+  if (order === 'recency') sessions.sort(byRecency)
+  return { key, workspaceId, cwd, createdAt, label, sessions }
 }
 
 /**
@@ -181,72 +130,24 @@ function groupByWorkspace(list: SessionListState, workspaces: readonly Workspace
   return groups
 }
 
-function sessionNode(s: SessionSummary, children: readonly SessionNode[], hasChildren: boolean, expanded: boolean): SessionNode {
+function sessionNode(s: SessionSummary): SessionNode {
   return {
     id: s.id,
     title: sessionTitle(s),
-    children,
-    hasChildren,
-    expanded,
     running: s.running,
     updatedAt: s.updatedAt,
   }
 }
 
-function buildVisible(g: Group, expandedSessions: ReadonlySet<string>): SessionNode[] {
-  const visited = new Set<SessionId>()
-  const walk = (id: SessionId): SessionNode | null => {
-    if (visited.has(id)) return null
-    visited.add(id)
-    const s = g.summaries.get(id)
-    /* v8 ignore next -- unreachable: walked ids come from the grouped summaries. */
-    if (s === undefined) return null
-    const kids = g.children.get(id) ?? []
-    const expanded = expandedSessions.has(id)
-    const children = expanded ? kids.map(walk).filter((n): n is SessionNode => n !== null) : []
-    return sessionNode(s, children, kids.length > 0, expanded)
-  }
-  return g.roots.map(walk).filter((n): n is SessionNode => n !== null)
-}
-
-/** Matched sessions plus their ancestor chains (forced visible under search). */
-function searchVisible(g: Group, q: string): Set<SessionId> {
-  const visible = new Set<SessionId>()
-  for (const m of g.summaries.values()) {
-    if (!sessionTitle(m).toLowerCase().includes(q)) continue
-    let cur: SessionSummary | undefined = m
-    while (cur !== undefined && !visible.has(cur.id)) {
-      visible.add(cur.id)
-      cur = cur.parentId !== undefined && cur.parentId !== cur.id ? g.summaries.get(cur.parentId) : undefined
-    }
-  }
-  return visible
-}
-
-function buildSearch(g: Group, visible: ReadonlySet<SessionId>): SessionNode[] {
-  const visited = new Set<SessionId>()
-  const walk = (id: SessionId): SessionNode | null => {
-    if (visited.has(id) || !visible.has(id)) return null
-    visited.add(id)
-    const s = g.summaries.get(id)
-    /* v8 ignore next -- unreachable: walked ids come from the grouped summaries. */
-    if (s === undefined) return null
-    const kids = (g.children.get(id) ?? []).filter(kid => visible.has(kid))
-    const children = kids.map(walk).filter((n): n is SessionNode => n !== null)
-    return sessionNode(s, children, kids.length > 0, kids.length > 0)
-  }
-  return g.roots.map(walk).filter((n): n is SessionNode => n !== null)
-}
-
 /**
- * Derive the nested workspace browser group structure.
+ * Derive the workspace browser groups with every session as a top-level row.
  *
  * Normal mode: every group shows; sessions populate under expanded groups,
- * descending only into expanded sessions. Search mode (non-blank query,
+ * preserving Host account order. Search mode (non-blank query,
  * case-insensitive display-title substring): expansion state is ignored —
- * matched sessions and their ancestor chains are forced visible, groups
- * without a display-title or label hit are dropped, and a label-only hit
- * keeps the bare group header. Blank sessions are excluded everywhere.
+ * matching sessions are forced visible, groups without a display-title or
+ * label hit are dropped, and a label-only hit
+ * keeps the bare group header. Non-current blank sessions are excluded.
  * @param list - sessions list snapshot (`current` feeds containsCurrent).
  * @param workspaces - real workspaces in stable Host order.
  * @param view - local expansion arrays and search query.
@@ -259,7 +160,6 @@ export function deriveGroups(
 ): GroupNode[] {
   const q = view.query.trim().toLowerCase()
   const expandedProjects = new Set(view.expandedProjects)
-  const expandedSessions = new Set(view.expandedSessions)
   const currentGroup = list.current === undefined
     ? undefined
     : (workspaces.find(w => w.sessionIds.includes(list.current as SessionId))?.workspaceId as string | undefined)
@@ -274,24 +174,24 @@ export function deriveGroups(
         cwd: g.cwd,
         createdAt: g.createdAt,
         label: g.label,
-        sessionCount: g.summaries.size,
+        sessionCount: g.sessions.length,
         expanded,
         containsCurrent: g.key === currentGroup,
-        sessions: expanded ? buildVisible(g, expandedSessions) : [],
+        sessions: expanded ? g.sessions.map(sessionNode) : [],
       })
     } else {
-      const visible = searchVisible(g, q)
-      if (visible.size === 0 && !g.label.toLowerCase().includes(q)) continue
+      const matches = g.sessions.filter(session => sessionTitle(session).toLowerCase().includes(q))
+      if (matches.length === 0 && !g.label.toLowerCase().includes(q)) continue
       groups.push({
         key: g.key,
         workspaceId: g.workspaceId,
         cwd: g.cwd,
         createdAt: g.createdAt,
         label: g.label,
-        sessionCount: g.summaries.size,
-        expanded: visible.size > 0,
+        sessionCount: g.sessions.length,
+        expanded: matches.length > 0,
         containsCurrent: g.key === currentGroup,
-        sessions: buildSearch(g, visible),
+        sessions: matches.map(sessionNode),
       })
     }
   }
@@ -301,9 +201,8 @@ export function deriveGroups(
 /**
  * Derive the flat session list ("In one list" mode): every session — fork
  * children included — as a top-level row, strictly newest-first. No grouping,
- * no parent/child adjacency; rows reuse SessionNode with children always
- * empty so the renderer stays branch-free. Search mode filters by
- * case-insensitive display-title substring.
+ * no parent/child adjacency. Search mode filters by case-insensitive
+ * display-title substring.
  * @param list - sessions list snapshot.
  * @param view - the search query (expansion state does not apply).
  * @returns flat rows in render order.
@@ -318,7 +217,7 @@ export function deriveFlat(list: SessionListState, view: Pick<TreeView, 'query'>
     rows.push(s)
   }
   rows.sort(byRecency)
-  return rows.map(s => sessionNode(s, [], false, false))
+  return rows.map(sessionNode)
 }
 
 /**

packages/client/ui-workspace/tests/rows.spec.tsx

@@ -56,46 +56,22 @@ describe('workspace browser rows', () => {
     expect(onToggle).toHaveBeenCalledOnce()
   })
 
-  it('renders and operates selected, running, recursive Session nodes', () => {
-    const child: SessionNode = {
-      id: sid('child'), title: 'Child', children: [], hasChildren: false,
-      expanded: false, running: false, updatedAt: 0,
-    }
-    const parent: SessionNode = {
-      id: sid('parent'), title: 'Parent', children: [child], hasChildren: true,
-      expanded: true, running: true, updatedAt: 0,
+  it('renders and opens a selected running Session row', () => {
+    const node: SessionNode = {
+      id: sid('session'), title: 'Session', running: true, updatedAt: 0,
     }
     const onOpen = vi.fn()
-    const onToggle = vi.fn()
-    const view = render(
-      <SessionNodeItem node={parent} depth={0} currentId={parent.id} now={0} onOpen={onOpen}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={onToggle} />,
+    render(
+      <SessionNodeItem node={node} currentId={node.id} now={0} onOpen={onOpen}
+        onRename={vi.fn()} onFork={vi.fn()} />,
     )
 
-    const parentRow = screen.getByText('Parent').closest('[role="treeitem"]')!
-    const childRow = screen.getByText('Child').closest('[role="treeitem"]')!
-    expect(parentRow.getAttribute('aria-selected')).toBe('true')
-    expect(parentRow.getAttribute('aria-expanded')).toBe('true')
-    expect(childRow.getAttribute('aria-selected')).toBe('false')
-    expect(childRow.hasAttribute('aria-expanded')).toBe(false)
-
-    fireEvent.click(screen.getByRole('button', { name: 'Collapse' }))
-    expect(onToggle).toHaveBeenCalledWith(parent.id)
-    expect(onOpen).not.toHaveBeenCalled()
-    fireEvent.click(parentRow)
-    fireEvent.click(childRow)
-    expect(onOpen.mock.calls).toEqual([[parent.id], [child.id]])
-
-    view.rerender(
-      <SessionNodeItem
-        node={{ ...parent, children: [], expanded: false, running: false }}
-        depth={1} currentId={undefined} now={0} onOpen={onOpen}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={onToggle}
-      />,
-    )
-    expect(screen.getByRole('button', { name: 'Expand' })).toBeTruthy()
-    expect(screen.getByRole('treeitem').getAttribute('aria-selected')).toBe('false')
-    expect(screen.getByRole('treeitem').style.paddingLeft).toBe('24px')
+    const row = screen.getByRole('treeitem')
+    expect(row.getAttribute('aria-selected')).toBe('true')
+    expect(row.hasAttribute('aria-expanded')).toBe(false)
+    expect(screen.queryByRole('button', { name: /Expand|Collapse/ })).toBeNull()
+    fireEvent.click(row)
+    expect(onOpen).toHaveBeenCalledWith(node.id)
   })
 
   it('workspace row menu opens on the ellipsis, renames, and shows the danger delete row', () => {
@@ -161,11 +137,10 @@ describe('workspace browser rows', () => {
     const onRename = vi.fn()
     const onFork = vi.fn()
     const node: SessionNode = {
-      id: sid('s1'), title: 'One', children: [], hasChildren: false,
-      expanded: false, running: false, updatedAt: 0,
+      id: sid('s1'), title: 'One', running: false, updatedAt: 0,
     }
-    render(<SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={onOpen}
-      onRename={onRename} onFork={onFork} onToggle={vi.fn()} />)
+    render(<SessionNodeItem node={node} currentId={undefined} now={0} onOpen={onOpen}
+      onRename={onRename} onFork={onFork} />)
     fireEvent.click(screen.getByRole('button', { name: 'Session actions for One' }))
     expect(onOpen).not.toHaveBeenCalled()
     expect(screen.getByRole('menuitem', { name: 'Delete session' }).className).toMatch(/danger/)
@@ -187,25 +162,14 @@ describe('workspace browser rows', () => {
     expect(screen.queryByRole('menu')).toBeNull()
   })
 
-  it('flat variant renders no twist even for a parent and ignores toggling', () => {
-    const node: SessionNode = {
-      id: sid('p'), title: 'Parent', children: [], hasChildren: true,
-      expanded: false, running: false, updatedAt: 0,
-    }
-    render(<SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={vi.fn()}
-      onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} flat />)
-    expect(screen.queryByRole('button', { name: 'Expand' })).toBeNull()
-  })
-
   it('shows the hover card after the dwell and suppresses it while the row menu is open', () => {
     vi.useFakeTimers()
     try {
       const node: SessionNode = {
-        id: sid('s1'), title: 'Hovered', children: [], hasChildren: false,
-        expanded: false, running: true, updatedAt: 0,
+        id: sid('s1'), title: 'Hovered', running: true, updatedAt: 0,
       }
-      render(<SessionNodeItem node={node} depth={0} currentId={undefined} now={60_000} onOpen={vi.fn()}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} />)
+      render(<SessionNodeItem node={node} currentId={undefined} now={60_000} onOpen={vi.fn()}
+        onRename={vi.fn()} onFork={vi.fn()} />)
       const wrapper = screen.getByRole('treeitem').parentElement as HTMLElement
       fireEvent.pointerEnter(wrapper)
       act(() => { vi.advanceTimersByTime(500) })
@@ -228,11 +192,10 @@ describe('workspace browser rows', () => {
     vi.useFakeTimers()
     try {
       const node: SessionNode = {
-        id: sid('s1'), title: 'Quiet', children: [], hasChildren: false,
-        expanded: false, running: false, updatedAt: 0,
+        id: sid('s1'), title: 'Quiet', running: false, updatedAt: 0,
       }
-      render(<SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={vi.fn()}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} />)
+      render(<SessionNodeItem node={node} currentId={undefined} now={0} onOpen={vi.fn()}
+        onRename={vi.fn()} onFork={vi.fn()} />)
       fireEvent.pointerEnter(screen.getByRole('treeitem').parentElement as HTMLElement)
       act(() => { vi.advanceTimersByTime(500) })
       expect(screen.getByText('Idle')).toBeTruthy()
@@ -244,13 +207,12 @@ describe('workspace browser rows', () => {
 
   it('draggable row wires start/end and gates hover/drop on an active same-group drag', () => {
     const node: SessionNode = {
-      id: sid('s1'), title: 'Drag me', children: [], hasChildren: false,
-      expanded: false, running: false, updatedAt: 0,
+      id: sid('s1'), title: 'Drag me', running: false, updatedAt: 0,
     }
     const inactive = dragProps()
     const { rerender } = render(
-      <SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={vi.fn()}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} drag={inactive} />,
+      <SessionNodeItem node={node} currentId={undefined} now={0} onOpen={vi.fn()}
+        onRename={vi.fn()} onFork={vi.fn()} drag={inactive} />,
     )
     const row = screen.getByRole('treeitem')
     stubRect(row)
@@ -267,8 +229,8 @@ describe('workspace browser rows', () => {
 
     const active = dragProps({ active: true, marker: 'before' })
     rerender(
-      <SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={vi.fn()}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} drag={active} />,
+      <SessionNodeItem node={node} currentId={undefined} now={0} onOpen={vi.fn()}
+        onRename={vi.fn()} onFork={vi.fn()} drag={active} />,
     )
     stubRect(screen.getByRole('treeitem'))
     // Top half hovers/drops 'before'; bottom half 'after' (row mid = 117).
@@ -281,8 +243,8 @@ describe('workspace browser rows', () => {
 
     const after = dragProps({ active: true, marker: 'after' })
     rerender(
-      <SessionNodeItem node={node} depth={0} currentId={undefined} now={0} onOpen={vi.fn()}
-        onRename={vi.fn()} onFork={vi.fn()} onToggle={vi.fn()} drag={after} />,
+      <SessionNodeItem node={node} currentId={undefined} now={0} onOpen={vi.fn()}
+        onRename={vi.fn()} onFork={vi.fn()} drag={after} />,
     )
     expect(screen.getByRole('treeitem').className).toMatch(/dropAfter/)
   })

packages/client/ui-workspace/tests/tree.spec.ts

@@ -21,7 +21,7 @@ const workspace = (id: string, sessionIds: string[]): WorkspaceView => ({
   sessionIds: sessionIds.map(sid), createdAt: '2026-01-01T00:00:00.000Z', updatedAt: '2026-01-01T00:00:00.000Z',
 })
 const view = (expandedProjects: readonly string[] = [], query = '') => ({
-  expandedProjects, expandedSessions: [] as string[], query,
+  expandedProjects, query,
 })
 
 describe('deriveGroups', () => {
@@ -74,7 +74,7 @@ describe('deriveGroups', () => {
     expect(groups[0]!.sessionCount).toBe(1)
   })
 
-  it('builds, sorts, expands, and cycle-guards an ungrouped session tree', () => {
+  it('ignores fork lineage and sorts every ungrouped session as a top-level row', () => {
     const parent = summary('parent', 1)
     const oldChild = { ...summary('old-child', 10), parentId: parent.id }
     const newChild = { ...summary('new-child', 20), parentId: parent.id }
@@ -87,15 +87,13 @@ describe('deriveGroups', () => {
     const groups = deriveGroups(
       list(parent, oldChild, newChild, tieB, tieA, self, orphan, cycleA, cycleB),
       [],
-      { expandedProjects: [UNGROUPED_KEY], expandedSessions: [parent.id, cycleA.id, cycleB.id], query: '' },
+      { expandedProjects: [UNGROUPED_KEY], query: '' },
     )
 
     expect(groups).toHaveLength(1)
     expect(groups[0]!.sessions.map(node => node.id)).toEqual([
-      sid('orphan'), sid('self'), parent.id, sid('cycle-a'),
-    ])
-    expect(groups[0]!.sessions[2]!.children.map(node => node.id)).toEqual([
       newChild.id, tieA.id, tieB.id, oldChild.id,
+      cycleB.id, cycleA.id, orphan.id, self.id, parent.id,
     ])
 
     // Equal timestamps use ids as a deterministic tiebreak in either input order.
@@ -113,7 +111,7 @@ describe('deriveGroups', () => {
     expect(groups[0]!.sessions.map(node => node.id)).toEqual([sid('present')])
   })
 
-  it('searches descendants with ancestors and handles cycles, self parents, and label-only hits', () => {
+  it('searches rows independently of lineage and keeps label-only hits', () => {
     const root = { ...summary('root', 1), displayTitle: 'Ancestor' }
     const match = { ...summary('match', 2), displayTitle: 'Needle child', parentId: root.id }
     const sibling = { ...summary('sibling', 3), displayTitle: 'Other child', parentId: root.id }
@@ -124,8 +122,8 @@ describe('deriveGroups', () => {
     const sessions = list(root, match, sibling, self, orphan, cycleA, cycleB)
     const groups = deriveGroups(sessions, [workspace('project', sessions.ids)], view([], 'needle'))
 
-    expect(groups[0]!.sessions.flatMap(node => [node.id, ...node.children.map(child => child.id)])).toEqual([
-      root.id, match.id, self.id, orphan.id, cycleA.id, cycleB.id,
+    expect(groups[0]!.sessions.map(node => node.id)).toEqual([
+      match.id, self.id, orphan.id, cycleA.id, cycleB.id,
     ])
 
     const labelOnly = deriveGroups(
@@ -157,8 +155,6 @@ describe('deriveFlat', () => {
     const tieA = summary('tie-a', 20)
     const rows = deriveFlat(list(parent, child, tieB, tieA), { query: '' })
     expect(rows.map(row => row.id)).toEqual([sid('child'), sid('tie-a'), sid('tie-b'), sid('parent')])
-    // Rows are branch-free: no children, no expansion.
-    expect(rows.every(row => row.children.length === 0 && !row.hasChildren && !row.expanded)).toBe(true)
   })
 
   it('search filters by case-insensitive display-title substring', () => {

packages/client/ui-workspace/tests/workspace-browser.spec.tsx

@@ -125,7 +125,7 @@ describe('WorkspaceBrowser', () => {
     expect(screen.queryByText('alpha-s')).toBeNull()
   })
 
-  it('unfolds a session subtree through the row twist', () => {
+  it('renders a fork child as a top-level row without a session twist', () => {
     const parent = summary('parent-s', 2)
     const child = { ...summary('child-s', 1), parentId: parent.id }
     mount({
@@ -133,11 +133,9 @@ describe('WorkspaceBrowser', () => {
       useWorkspaces: hook(workspaceState([workspace('alpha', ['parent-s', 'child-s'])])),
     })
     fireEvent.click(screen.getByText('alpha'))
-    expect(screen.queryByText('child-s')).toBeNull()
-    fireEvent.click(screen.getByRole('button', { name: 'Expand' }))
     expect(screen.getByText('child-s')).toBeTruthy()
-    fireEvent.click(screen.getByRole('button', { name: 'Collapse' }))
-    expect(screen.queryByText('child-s')).toBeNull()
+    expect(screen.queryByRole('button', { name: /Expand|Collapse/ })).toBeNull()
+    expect(screen.getByText('child-s').closest('[role="treeitem"]')?.getAttribute('draggable')).toBe('true')
   })
 
   it('auto-expands the selected session group and starts a session from the group ＋', () => {