fix(native-chat): ask which workspace the composer serves now

The IME-flush ownership check compared the workspace id captured when the
drop happened against the same captured value, so for a structured pane the
comparison could only ever hold. The live protection came from the host and
owner checks beside it; this one asked nothing.

Read the id through a ref so the check means what it reads as. A pane whose
structured target moves between the drop and the composition settling now
refuses the queued path instead of attaching it.

src/renderer/src/components/native-chat/native-chat-composer-workspace-file-drop.test.tsx

@@ -111,6 +111,8 @@ type ProbeProps = {
   disabled?: boolean
   initialDraft?: string
   structured?: boolean
+  /** Overrides only the structured target, leaving the pane's scope key alone. */
+  structuredWorkspaceId?: string
   workspaceId?: string
 }
 
@@ -121,6 +123,7 @@ function ComposerProbe({
   disabled = false,
   initialDraft = '',
   structured = true,
+  structuredWorkspaceId,
   workspaceId = 'worktree-1'
 }: ProbeProps): React.JSX.Element {
   const [draft, setDraft] = useState(initialDraft)
@@ -143,7 +146,7 @@ function ComposerProbe({
   })
   const workspaceFileDropHandlers = useNativeChatWorkspaceFileDrop({
     terminalTabId: 'terminal-tab-1',
-    structuredWorktreeId: structured ? workspaceId : undefined,
+    structuredWorktreeId: structured ? (structuredWorkspaceId ?? workspaceId) : undefined,
     disabled,
     attachResolvedPaths: attachments.attachResolvedPaths,
     setNotice
@@ -244,6 +247,7 @@ describe('native chat workspace file drops', () => {
     testState.ownerSshGeneration = 4
     testState.ownerWorktreePath = '/remote/repo'
     testState.targetIsRemoteRuntime = false
+    testState.store.tabsByWorktree = { 'worktree-1': [{ id: 'terminal-tab-1' }] }
     latestInput = null
     bubbledDrop.mockReset()
   })
@@ -425,6 +429,21 @@ describe('native chat workspace file drops', () => {
     expect(screen.getByText('Files can only be attached to their source workspace.')).toBeTruthy()
   })
 
+  // The queued check must ask which workspace this composer serves NOW. Comparing
+  // a captured id against itself would pass no matter where the pane ended up.
+  it('rejects an IME-queued path when the pane changes workspace before settling', () => {
+    const view = render(<ComposerProbe initialDraft="preedit" />)
+    const input = editor()
+    fireEvent.compositionStart(input)
+    dispatchDragEvent('drop', input, internalTransfer(['/repo/a.ts']))
+
+    view.rerender(<ComposerProbe initialDraft="preedit" structuredWorkspaceId="worktree-2" />)
+    fireEvent.compositionEnd(input, { data: '' })
+
+    expect(screen.getByTestId('draft').textContent).toBe('preedit')
+    expect(screen.getByText('Files can only be attached to their source workspace.')).toBeTruthy()
+  })
+
   it('rejects only the exact unresolved-owner sentinel', () => {
     testState.executionHostId = 'runtime:unresolved-owner'
     const view = render(<ComposerProbe />)

src/renderer/src/components/native-chat/use-native-chat-workspace-file-drop.ts

@@ -1,4 +1,4 @@
-import { useCallback, type DragEventHandler } from 'react'
+import { useCallback, useLayoutEffect, useRef, type DragEventHandler } from 'react'
 import { useAppStore } from '@/store'
 import { getExecutionHostIdForWorktree } from '@/lib/worktree-runtime-owner'
 import {
@@ -67,6 +67,14 @@ export function useNativeChatWorkspaceFileDrop({
   structuredWorktreeId,
   terminalTabId
 }: Args): WorkspaceFileDropHandlers {
+  // The IME-flush check runs against a closure captured at drop time. Reading
+  // the prop through a ref keeps "is this still my workspace?" a real question
+  // rather than a comparison of one captured value against itself.
+  const structuredWorktreeIdRef = useRef(structuredWorktreeId)
+  useLayoutEffect(() => {
+    structuredWorktreeIdRef.current = structuredWorktreeId
+  }, [structuredWorktreeId])
+
   const onDragOverCapture = useCallback<DragEventHandler<HTMLDivElement>>(
     (event) => {
       if (!hasWorkspaceFileDragType(event.dataTransfer)) {
@@ -130,7 +138,7 @@ export function useNativeChatWorkspaceFileDrop({
       const targetOwnerIsCurrent = (): boolean => {
         const currentState = useAppStore.getState()
         const currentWorkspaceId =
-          structuredWorktreeId ??
+          structuredWorktreeIdRef.current ??
           findTerminalTabWorktreeId(currentState.tabsByWorktree, terminalTabId)
         if (currentWorkspaceId !== source.workspaceId) {
           return false
@@ -139,7 +147,7 @@ export function useNativeChatWorkspaceFileDrop({
         const currentOwner = resolveNativeChatAttachmentOwnerForWorktree(
           currentState,
           currentWorkspaceId,
-          structuredWorktreeId ? undefined : terminalTabId
+          structuredWorktreeIdRef.current ? undefined : terminalTabId
         )
         return (
           isResolvedWorkspaceFileDragExecutionHost(currentHostId) &&