fix(worktrees): protect user changes across ambiguous move failures

Post-merge hardening of the session-to-worktree move (#2998), driven by
review findings on the follow-up pass:

- an ambiguous transport failure (relay abort, timeout) on the
  change-carrying move no longer force-deletes the fresh worktree that
  may hold the user's only copy of their changes; both intent kinds
  surface honest guidance and refresh both directories
- assertSdkSuccess re-tags ambiguous transport errors when wrapping SDK
  failures, so ambiguity classification survives the wrapper on every
  path, matching the prompt-send precedent
- session liveness checks scan all child stores plus the global status
  index, and report unknown (not idle) when no store covers the session
  — an evicted background directory can no longer make a busy session
  look movable
- incomplete-rollback errors carry the changes-may-be-in-destination
  guidance instead of swallowing it
- move-message assembly shared across the three call sites; tests now
  exercise the real ambiguity classifier (extracted to
  send-failure-classification.ts) instead of a hand-mirrored mock
- i18n fallout from the merge train: Turkish gains the 21 worktree-move
  keys, all 12 locales get the hedged ambiguous-failure toast; owning
  DOCUMENTATION.md files record the new contracts

packages/ui/src/components/layout/Header.tsx

@@ -71,7 +71,7 @@ import { copyTextToClipboard } from '@/lib/clipboard';
 import { buildExportFilename, downloadAsMarkdown, formatSessionAsMarkdown, saveAsMarkdownDesktop } from '@/lib/exportSession';
 import { Dialog, DialogContent, DialogDescription, DialogFooter, DialogHeader, DialogTitle } from '@/components/ui/dialog';
 import { Button } from '@/components/ui/button';
-import { requestSessionTreeMove, useIsSessionWorktreeMovePending } from '@/lib/worktrees/sessionWorktreeMove';
+import { buildSessionTreeMoveMessages, requestSessionTreeMove, useIsSessionWorktreeMovePending } from '@/lib/worktrees/sessionWorktreeMove';
 
 const DESKTOP_HEADER_ICON_BUTTON_CLASS = 'app-region-no-drag inline-flex h-8 w-8 items-center justify-center gap-2 rounded-md typography-ui-label font-medium text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary disabled:pointer-events-none disabled:opacity-50 hover:bg-interactive-hover transition-colors';
 
@@ -1064,12 +1064,10 @@ export const Header: React.FC = () => {
       root,
       descendants,
       sourceDirectory: sessionDirectory,
-      messages: {
-        success: t('sessions.sidebar.session.moveToWorktree.success'),
-        failure: t('sessions.sidebar.session.moveToWorktree.failed'),
-        sourceVerificationFailed: t('sessions.sidebar.session.moveToWorktree.sourceVerificationFailed'),
-        applyChangesFailed: t('sessions.sidebar.session.moveToWorktree.applyChangesFailed'),
-      },
+      messages: buildSessionTreeMoveMessages(t, {
+        success: 'sessions.sidebar.session.moveToWorktree.success',
+        failure: 'sessions.sidebar.session.moveToWorktree.failed',
+      }),
     });
   }, [currentSessionId, isCurrentSessionActive, isCurrentSessionMovingToWorktree, sessionDirectory, t]);
 

packages/ui/src/components/session/sidebar/DOCUMENTATION.md

@@ -20,6 +20,12 @@ kept at this root in `types.ts` and `utils.tsx`.
   changes and roll back session-only if a later descendant fails. The root moves
   last and carries source changes once, which prevents rollback from replaying the
   transferred patch into the source.
+- Failure cleanup: a worktree created for the move is removed only after a
+  definite failure. When the change-carrying request fails without confirming
+  its outcome, that worktree is KEPT (it may hold the only copy of the user's
+  changes), both directories are refreshed authoritatively because the session
+  may have moved server-side, and the toast points the user at the destination.
+  Existing destinations are never removed; they get the same guidance.
 
 `MainLayout` and `VSCodeLayout` call `useSessionListSync({ isVSCode })`
 unconditionally. The hook publishes complete directory bootstrap demand,

packages/ui/src/components/session/sidebar/SessionWorktreeMoveConfirmDialog.test.tsx

@@ -33,6 +33,7 @@ const makeMoveMessages = (): SessionTreeMoveMessages => ({
   failure: 'move failed',
   sourceVerificationFailed: 'source verification failed',
   applyChangesFailed: 'apply changes failed',
+  changesMayBeInDestination: 'changes may be in destination',
 });
 
 const makeExistingIntent = (): SessionTreeMoveIntent => ({

packages/ui/src/components/session/sidebar/sessions/SessionNodeItem.tsx

@@ -48,6 +48,7 @@ import { MultiRunFusionDialog } from '@/components/multirun/MultiRunFusionDialog
 import { FusionIcon } from '@/components/icons/FusionIcon';
 import { RuntimeAPIContext } from '@/contexts/runtimeAPIContext';
 import {
+  buildSessionTreeMoveMessages,
   requestSessionTreeMove,
   useIsSessionWorktreeMovePending,
 } from '@/lib/worktrees/sessionWorktreeMove';
@@ -1047,12 +1048,10 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
                         descendants: collectNodeDescendantSessions(node),
                         sourceDirectory: sessionDirectory,
                         destination: target.metadata,
-                        messages: {
-                          success: t('sessions.sidebar.session.moveToWorktree.existingSuccess'),
-                          failure: t('sessions.sidebar.session.moveToWorktree.existingFailed'),
-                          sourceVerificationFailed: t('sessions.sidebar.session.moveToWorktree.sourceVerificationFailed'),
-                          applyChangesFailed: t('sessions.sidebar.session.moveToWorktree.applyChangesFailed'),
-                        },
+                        messages: buildSessionTreeMoveMessages(t, {
+                          success: 'sessions.sidebar.session.moveToWorktree.existingSuccess',
+                          failure: 'sessions.sidebar.session.moveToWorktree.existingFailed',
+                        }),
                       });
                     }}
                   >
@@ -1086,12 +1085,10 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
                       root: resolvedSession,
                       descendants: collectNodeDescendantSessions(node),
                       sourceDirectory: sessionDirectory,
-                      messages: {
-                        success: t('sessions.sidebar.session.moveToWorktree.success'),
-                        failure: t('sessions.sidebar.session.moveToWorktree.failed'),
-                        sourceVerificationFailed: t('sessions.sidebar.session.moveToWorktree.sourceVerificationFailed'),
-                        applyChangesFailed: t('sessions.sidebar.session.moveToWorktree.applyChangesFailed'),
-                      },
+                      messages: buildSessionTreeMoveMessages(t, {
+                        success: 'sessions.sidebar.session.moveToWorktree.success',
+                        failure: 'sessions.sidebar.session.moveToWorktree.failed',
+                      }),
                     });
                   }}
                   className="[&>svg]:mr-1"