Merge remote-tracking branch 'origin/master' into mergebot/pr711

# Conflicts:
#	apps/cli/README.i18n.yaml
#	apps/cli/README.md
#	apps/cli/README.zh.md
#	apps/cli/cordis.yml
#	apps/cli/package.json
#	docs/config-catalog.md
#	packages/client/runtime/README.i18n.yaml
#	packages/client/runtime/src/client/contract/sessions.ts
#	packages/client/test-runtime/src/sessions.ts
#	packages/client/ui-workspace/README.i18n.yaml
#	packages/client/ui-workspace/README.md
#	packages/client/ui-workspace/README.zh.md
#	packages/client/ui-workspace/src/client/WorkspaceBrowser.tsx
#	packages/client/ui-workspace/src/client/tree.ts
#	packages/client/ui-workspace/tests/apply.spec.ts
#	packages/client/ui-workspace/tests/tree.spec.ts
#	packages/host/apiproxy/README.i18n.yaml
#	packages/host/apiproxy/src/api-proxy.ts
#	packages/host/apiproxy/src/api/index.ts
#	packages/host/apiproxy/tests/client-handler.spec.ts
#	packages/host/apiproxy/tests/rpc-schemas.spec.ts
#	pnpm-lock.yaml

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

@@ -100,7 +100,7 @@ interface DragState {
 
 type SessionTreeProps = Pick<
   WorkspaceBrowserProps,
-  'useSessions' | 'startSession' | 'open' | 'insertSessionBefore'
+  'useSessions' | 'startSession' | 'open' | 'forkSession' | 'insertSessionBefore'
 > & {
   workspaces: readonly WorkspaceView[]
   /** Open the browser-owned rename dialog for a real Workspace group. */
@@ -113,13 +113,12 @@ type SessionTreeProps = Pick<
 
 /** The scrolling session tree; unmounting at collapse settle drops the sessions subscription and expansion state. */
 function SessionTree({
-  useSessions, startSession, open, workspaces,
+  useSessions, startSession, open, forkSession, workspaces,
   onRenameRequest, onDeleteRequest, onSessionRename, insertSessionBefore,
 }: SessionTreeProps) {
   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
@@ -131,8 +130,8 @@ function SessionTree({
     setExpandedProjects(l => (l.includes(currentGroup) ? l : [...l, currentGroup]))
   }, [current, currentGroup])
   const groups = useMemo(
-    () => deriveGroups(list, workspaces, { expandedProjects, expandedSessions }),
-    [list, workspaces, expandedProjects, expandedSessions],
+    () => deriveGroups(list, workspaces, { expandedProjects }),
+    [list, workspaces, expandedProjects],
   )
   const now = Date.now()
 
@@ -143,7 +142,7 @@ function SessionTree({
           <div className={css.empty}>No sessions yet</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}>
@@ -167,7 +166,7 @@ function SessionTree({
                 }}
             />
             {group.sessions.map((node, index) => {
-              // Draggable: real-workspace group roots. The drag
+              // Draggable: real-workspace session rows. 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
@@ -185,15 +184,15 @@ 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)
@@ -205,12 +204,11 @@ function SessionTree({
                 <SessionNodeItem
                   key={node.id}
                   node={node}
-                  depth={0}
                   currentId={current}
                   now={now}
                   onOpen={open}
                   onRename={onSessionRename}
-                  onToggle={(id) => { setExpandedSessions(l => toggled(l, id)) }}
+                  onFork={forkSession}
                   drag={dragProps}
                 />
               )
@@ -224,7 +222,7 @@ function SessionTree({
 }
 
 /** The flat "In one list" body: every session a top-level row, newest-first. */
-function FlatList({ useSessions, open, onSessionRename }: Pick<SessionTreeProps, 'useSessions' | 'open' | 'onSessionRename'>) {
+function FlatList({ useSessions, open, forkSession, onSessionRename }: Pick<SessionTreeProps, 'useSessions' | 'open' | 'forkSession' | 'onSessionRename'>) {
   const list = useSessions(s => s)
   const rows = useMemo(() => deriveFlat(list), [list])
   const now = Date.now()
@@ -238,14 +236,11 @@ function FlatList({ useSessions, open, onSessionRename }: Pick<SessionTreeProps,
           <SessionNodeItem
             key={node.id}
             node={node}
-            depth={0}
             currentId={list.current}
             now={now}
             onOpen={open}
             onRename={onSessionRename}
-            /* v8 ignore next -- required-prop filler: flat rows render no twist, so it never fires. */
-            onToggle={() => {}}
-            flat
+            onFork={forkSession}
           />
         ))}
       </div>
@@ -336,6 +331,7 @@ export function WorkspaceBrowser({
   startSession,
   open,
   renameSession,
+  forkSession,
   renameWorkspace,
   deleteWorkspace,
   insertSessionBefore,
@@ -602,11 +598,12 @@ export function WorkspaceBrowser({
             />
           )
           : groupBy === 'flat'
-            ? <FlatList useSessions={useSessions} open={open} onSessionRename={onSessionRename} />
+            ? <FlatList useSessions={useSessions} open={open} forkSession={forkSession} onSessionRename={onSessionRename} />
             : (
               <SessionTree
                 useSessions={useSessions}
                 onSessionRename={onSessionRename}
+                forkSession={forkSession}
                 workspaces={workspaces}
                 startSession={startSession}
                 open={open}

packages/client/ui-workspace/src/client/contract/slots.ts

@@ -107,6 +107,8 @@ export type WorkspaceBrowserInjected = DirectoryPickingInjected & {
   searchResultLimit: number
   /** Rename a Session (explicit user title; resolves on host acceptance). */
   renameSession: (sessionId: SessionId, title: string) => Promise<void>
+  /** Fork a Session at its last completed turn and open the child. */
+  forkSession: (sessionId: SessionId) => void
   /** Rename a Host Workspace (rejects on name conflict; resolves on durability). */
   renameWorkspace: (workspaceId: WorkspaceId, title: string) => Promise<void>
   /** Delete only a Host Workspace registration; directory and Session logs remain. */

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

@@ -66,6 +66,13 @@ export function apply(ctx: ClientContext): void {
       const result = await session.rename(title)
       if (!result.ok) throw new Error(result.error.message)
     },
+    forkSession: (sessionId) => {
+      ctx.sessions.fork({ sessionId, increaseTitle: true })
+        .then((childId) => { ctx.sessions.open(childId) })
+        .catch(() => {
+          // Fork or child-rename failure keeps the current selection.
+        })
+    },
     renameWorkspace: async (workspaceId, title) => { await ctx.workspaces.rename(workspaceId, title) },
     deleteWorkspace: async (workspaceId) => { await ctx.workspaces.delete(workspaceId) },
     insertSessionBefore: async (workspaceId, sessionId, beforeSessionId) => {

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

@@ -97,9 +97,7 @@
   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;
@@ -226,7 +224,7 @@
   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);
@@ -250,6 +248,13 @@
   overflow-wrap: break-word;
 }
 
+.hoverPath {
+  font-size: 12px;
+  line-height: 16px;
+  color: #CFD3D6;
+  word-break: break-all;
+}
+
 .hoverTime {
   font-size: 12px;
   line-height: 16px;
@@ -284,33 +289,9 @@
   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

@@ -2,8 +2,8 @@
  * Workspace browser tree row components (figma Cell set 14:3080): pure presentational —
  * all data and callbacks arrive via props. Hover swaps (folder->chevron,
  * time->ellipsis, action buttons) are CSS-only. Row ... menus are visual-only
- * except workspace Rename/Delete and session Rename; the session hover card is
- * suppressed while a menu is open.
+ * except workspace Rename/Delete and session Rename/Fork; the session and
+ * workspace hover cards are suppressed while a menu is open.
  */
 import { useState } from 'react'
 import clsx from 'clsx'
@@ -16,9 +16,6 @@ import type { GroupNode, SearchResultNode, 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 /> },
@@ -30,10 +27,26 @@ const WORKSPACE_MENU_ITEMS = [
   { id: 'delete', label: 'Delete workspace', icon: <IconTrashOutline16 />, danger: true },
 ]
 
+/** Hover-card body: workspace title, full directory path, absolute creation time. */
+function WorkspaceHoverContent({ label, cwd, createdAt }: {
+  label: string
+  cwd: string | undefined
+  createdAt: number
+}) {
+  return (
+    <div className={css.hoverContent}>
+      <div className={css.hoverTitle}>{label}</div>
+      <div className={css.hoverPath}>{cwd}</div>
+      <div className={css.hoverTime}>{`Created ${new Date(createdAt).toLocaleString()}`}</div>
+    </div>
+  )
+}
+
 /**
  * Project (workspace) header row: 54px, folder + title + session count;
- * hover reveals the chevron and create button. `containsCurrent` arrives on
- * the node (derivation fact, no renderer scan).
+ * hover reveals the chevron and create button, and dwelling on a real
+ * Workspace shows its hover card (the ungrouped bucket has none).
+ * `containsCurrent` arrives on the node (derivation fact, no renderer scan).
  * @param props.group - derived group node.
  * @param props.onToggle - expand/collapse the group.
  * @param props.onCreate - start a frontend Session inside this Workspace.
@@ -50,7 +63,7 @@ export function ProjectRowItem({ group, onToggle, onCreate, actions }: {
   const active = group.expanded && group.containsCurrent
   const count = `${row.sessionCount} ${row.sessionCount === 1 ? 'session' : 'sessions'}`
   const [menuOpen, setMenuOpen] = useState(false)
-  return (
+  const ownRow = (
     <div
       className={clsx(css.projectRow, menuOpen && css.menuOpen)}
       role="treeitem"
@@ -107,19 +120,24 @@ export function ProjectRowItem({ group, onToggle, onCreate, actions }: {
       </span>
     </div>
   )
+  // The ungrouped bucket has no backing Workspace: no card to show.
+  if (row.createdAt === undefined) return ownRow
+  return (
+    <HoverCard
+      anchor={ownRow}
+      content={<WorkspaceHoverContent label={row.label} cwd={row.cwd} createdAt={row.createdAt} />}
+      disabled={menuOpen}
+    />
+  )
 }
 
 /**
- * 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 }) {
@@ -136,7 +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).
  */
@@ -194,26 +212,22 @@ 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, 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
   /** Open the browser-owned session rename dialog (row menu action). */
   onRename: (id: SessionNode['id'], currentTitle: string) => void
-  onToggle: (id: SessionNode['id']) => void
-  /** Present only on draggable rows (workspace-group roots outside search). */
+  /** Fork a session at its last completed turn (row menu action). */
+  onFork: (id: SessionNode['id']) => void
+  /** 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(
@@ -222,8 +236,6 @@ 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
@@ -249,18 +261,6 @@ 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>
@@ -271,7 +271,8 @@ export function SessionNodeItem({ node, depth, currentId, now, onOpen, onRename,
           items={SESSION_MENU_ITEMS}
           onSelect={(id) => {
             setMenuOpen(false)
-            if (id === 'rename') onRename(node.id, row.title) // fork/delete stay visual-only.
+            if (id === 'rename') onRename(node.id, row.title)
+            if (id === 'fork') onFork(node.id) // delete stays visual-only.
           }}
           portal
           closeOnPointerLeave
@@ -290,24 +291,10 @@ 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}
-          onToggle={onToggle}
-        />
-      ))}
-    </>
+    <HoverCard
+      anchor={ownRow}
+      content={<SessionHoverContent node={node} now={now} />}
+      disabled={menuOpen || drag?.active === true}
+    />
   )
 }

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

@@ -13,33 +13,30 @@ 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-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
   /** Backing Workspace id; absent only for the ungrouped bucket. */
   workspaceId: WorkspaceId | undefined
   cwd: string | undefined
+  /** Workspace creation time (epoch ms); absent only for the ungrouped bucket. */
+  createdAt: number | undefined
   label: string
   /** Total visible sessions in the group. */
   sessionCount: number
   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[]
 }
 
@@ -58,20 +55,18 @@ export interface SearchResultSet {
   hasMore: boolean
 }
 
-/** 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[]
 }
 
 interface Group {
   key: string
   workspaceId: WorkspaceId | undefined
   cwd: string | undefined
+  createdAt: number | undefined
   label: string
-  summaries: Map<SessionId, SessionSummary>
-  roots: SessionId[]
-  children: Map<SessionId, SessionId[]>
+  sessions: SessionSummary[]
 }
 
 /**
@@ -102,63 +97,21 @@ 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,
   cwd: string | undefined,
+  createdAt: number | undefined,
   label: string,
   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, 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 }
 }
 
 /**
@@ -179,7 +132,8 @@ function groupByWorkspace(list: SessionListState, workspaces: readonly Workspace
       members.push(summary)
     }
     groups.push(buildGroup(
-      workspace.workspaceId, workspace.workspaceId, workspace.path, workspace.title, members, 'account',
+      workspace.workspaceId, workspace.workspaceId, workspace.path,
+      Date.parse(workspace.createdAt), workspace.title, members, 'account',
     ))
   }
   const stray = list.ids
@@ -187,45 +141,27 @@ function groupByWorkspace(list: SessionListState, workspaces: readonly Workspace
     .filter((s): s is SessionSummary =>
       s !== undefined && !accounted.has(s.id) && sessionVisible(s, list.current))
   if (stray.length > 0) {
-    groups.push(buildGroup(UNGROUPED_KEY, undefined, undefined, UNGROUPED_LABEL, stray, 'recency'))
+    groups.push(buildGroup(UNGROUPED_KEY, undefined, undefined, undefined, UNGROUPED_LABEL, stray, 'recency'))
   }
   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)
-}
-
 /**
- * Derive the nested workspace browser group structure.
+ * Derive the workspace browser groups with every session as a top-level row.
  *
- * Every group shows; sessions populate under expanded groups, descending
- * only into expanded sessions. Blank sessions are excluded except for the
- * selected provisional New Session row.
+ * Every group shows; sessions populate under expanded groups, preserving
+ * Host account order. Blank sessions are excluded except for the selected
+ * provisional New Session row. Content search lives outside this derivation
+ * (see {@link deriveSearchResults}).
  * @param list - sessions list snapshot (`current` feeds containsCurrent).
  * @param workspaces - real workspaces in stable Host order.
  * @param view - local expansion arrays.
@@ -237,7 +173,6 @@ export function deriveGroups(
   view: TreeView,
 ): GroupNode[] {
   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)
@@ -249,11 +184,12 @@ export function deriveGroups(
       key: g.key,
       workspaceId: g.workspaceId,
       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) : [],
     })
   }
   return groups
@@ -262,8 +198,8 @@ 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.
+ * no parent/child adjacency. Content search lives outside this derivation
+ * (see {@link deriveSearchResults}).
  * @param list - sessions list snapshot.
  * @returns flat rows in render order.
  */
@@ -275,7 +211,7 @@ export function deriveFlat(list: SessionListState): SessionNode[] {
     rows.push(s)
   }
   rows.sort(byRecency)
-  return rows.map(s => sessionNode(s, [], false, false))
+  return rows.map(sessionNode)
 }
 
 /**