fix(desktop): upload Windows attachments to Linux backends

apps/desktop/src/app/chat/session-tile-actions.ts

@@ -169,7 +169,12 @@ export function useSessionTileActions({ runtimeId, scope, storedSessionId }: Ses
         }
 
         if (attachment.kind === 'image' || attachment.kind === 'file') {
-          const next = await uploadComposerAttachment(attachment, { remote, requestGateway, sessionId })
+          const next = await uploadComposerAttachment(attachment, {
+            backendCwd: readState()?.cwd,
+            remote,
+            requestGateway,
+            sessionId
+          })
 
           if (options.updateComposerAttachments ?? true) {
             scope.attachments.update(next)

apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx

@@ -12,6 +12,7 @@ import { $notifications, clearNotifications } from '@/store/notifications'
 import {
   $busy,
   $connection,
+  $currentCwd,
   $currentUsage,
   $messages,
   $sessions,
@@ -2128,6 +2129,7 @@ describe('usePromptActions file attachment sync', () => {
   afterEach(() => {
     cleanup()
     $connection.set(null)
+    $currentCwd.set('')
     vi.restoreAllMocks()
   })
 
@@ -2190,6 +2192,100 @@ describe('usePromptActions file attachment sync', () => {
     })
   })
 
+
+  it('uploads Windows file bytes when local mode fronts a POSIX WSL/Docker backend', async () => {
+    $connection.set({ mode: 'local' } as never)
+    $currentCwd.set('/root')
+    const readFileDataUrl = vi.fn(async () => 'data:text/plain;base64,aGVsbG8=')
+    Object.defineProperty(window, 'hermesDesktop', {
+      configurable: true,
+      value: { readFileDataUrl }
+    })
+
+    const attachment: ComposerAttachment = {
+      ...fileAttachment(),
+      path: 'C:\\Users\\alice\\Downloads\\report.txt',
+      refText: '@file:`C:\\Users\\alice\\Downloads\\report.txt`'
+    }
+    const calls: { method: string; params?: Record<string, unknown> }[] = []
+
+    const requestGateway = vi.fn(async (method: string, params?: Record<string, unknown>) => {
+      calls.push({ method, params })
+
+      if (method === 'file.attach') {
+        return {
+          attached: true,
+          path: '/root/.hermes/desktop-attachments/report.txt',
+          ref_text: '@file:.hermes/desktop-attachments/report.txt',
+          uploaded: true
+        } as never
+      }
+
+      return {} as never
+    })
+
+    let handle: HarnessHandle | null = null
+    await actRender(
+      <Harness onReady={h => (handle = h)} refreshSessions={async () => undefined} requestGateway={requestGateway} />
+    )
+
+    expect(await handle!.submitText('summarize', { attachments: [attachment] })).toBe(true)
+    expect(readFileDataUrl).toHaveBeenCalledWith('C:\\Users\\alice\\Downloads\\report.txt')
+    expect(calls[0]).toEqual({
+      method: 'file.attach',
+      params: {
+        data_url: 'data:text/plain;base64,aGVsbG8=',
+        name: 'report.txt',
+        path: 'C:\\Users\\alice\\Downloads\\report.txt',
+        session_id: RUNTIME_SESSION_ID
+      }
+    })
+    expect(calls[1]).toEqual({
+      method: 'prompt.submit',
+      params: { session_id: RUNTIME_SESSION_ID, text: '@file:.hermes/desktop-attachments/report.txt\n\nsummarize' }
+    })
+  })
+
+  it('uses image.attach_bytes for a Windows image when the local backend cwd is POSIX', async () => {
+    const readFileDataUrl = vi.fn(async () => 'data:image/jpeg;base64,aGVsbG8=')
+    Object.defineProperty(window, 'hermesDesktop', {
+      configurable: true,
+      value: { readFileDataUrl }
+    })
+
+    const requestGateway = vi.fn(async (method: string) => {
+      if (method === 'image.attach_bytes') {
+        return { attached: true, path: '/root/tmp/photo.jpg' } as never
+      }
+
+      return {} as never
+    })
+
+    const uploaded = await uploadComposerAttachment(
+      {
+        id: 'image:photo.jpg',
+        kind: 'image',
+        label: 'photo.jpg',
+        path: 'C:\\Users\\alice\\Pictures\\photo.jpg'
+      },
+      {
+        backendCwd: '/root',
+        remote: false,
+        requestGateway,
+        sessionId: RUNTIME_SESSION_ID
+      }
+    )
+
+    expect(readFileDataUrl).toHaveBeenCalledWith('C:\\Users\\alice\\Pictures\\photo.jpg')
+    expect(requestGateway).toHaveBeenCalledWith('image.attach_bytes', {
+      content_base64: 'aGVsbG8=',
+      filename: 'photo.jpg',
+      session_id: RUNTIME_SESSION_ID
+    })
+    expect(requestGateway).not.toHaveBeenCalledWith('image.attach', expect.anything())
+    expect(uploaded.path).toBe('/root/tmp/photo.jpg')
+  })
+
   it('passes a path-less @file: ref straight through (no path = nothing to upload)', async () => {
     // Submit-layer contract: only attachments that carry a `path` are upload
     // candidates. A path-less ref (an @-mention/context ref or pasted text)
@@ -2237,8 +2333,20 @@ describe('usePromptActions file attachment sync', () => {
     expect(calls[0]?.params?.text).toContain('@file:`/Users/mahmoud/Downloads/DEVIS_signed.pdf`')
   })
 
-  it('passes the path directly via file.attach in local mode (no byte upload)', async () => {
+  it('passes a Windows path directly for a native Windows local backend', async () => {
     $connection.set({ mode: 'local' } as never)
+    $currentCwd.set('C:\\Users\\alice\\project')
+    const readFileDataUrl = vi.fn(async () => 'data:text/plain;base64,c2hvdWxkLW5vdC1iZS1yZWFk')
+    Object.defineProperty(window, 'hermesDesktop', {
+      configurable: true,
+      value: { readFileDataUrl }
+    })
+
+    const attachment: ComposerAttachment = {
+      ...fileAttachment(),
+      path: 'C:\\Users\\alice\\Downloads\\report.txt',
+      refText: '@file:`C:\\Users\\alice\\Downloads\\report.txt`'
+    }
 
     const calls: { method: string; params?: Record<string, unknown> }[] = []
 
@@ -2257,11 +2365,12 @@ describe('usePromptActions file attachment sync', () => {
       <Harness onReady={h => (handle = h)} refreshSessions={async () => undefined} requestGateway={requestGateway} />
     )
 
-    const ok = await handle!.submitText('summarize', { attachments: [fileAttachment()] })
+    const ok = await handle!.submitText('summarize', { attachments: [attachment] })
 
     expect(ok).toBe(true)
     expect(calls[0]?.method).toBe('file.attach')
-    // Local mode sends no data_url — the gateway shares this disk.
+    expect(readFileDataUrl).not.toHaveBeenCalled()
+    // Native Windows local mode shares the same path namespace.
     expect(calls[0]?.params).not.toHaveProperty('data_url')
     expect(calls[1]).toEqual({
       method: 'prompt.submit',

apps/desktop/src/app/session/hooks/use-prompt-actions/index.ts

@@ -25,6 +25,7 @@ import { clearAllPrompts } from '@/store/prompts'
 import {
   $busy,
   $connection,
+  $currentCwd,
   $messages,
   setAwaitingResponse,
   setBusy,
@@ -76,26 +77,38 @@ interface HandoffResult {
   error?: string
 }
 
+const WINDOWS_ABSOLUTE_PATH_RE = /^(?:[A-Za-z]:[\\/]|\\\\)/
+const POSIX_ABSOLUTE_PATH_RE = /^\/(?!\/)/
+
+// `mode: local` means the gateway was launched locally, not necessarily that
+// Electron and the gateway share a filesystem. Windows Desktop can front a
+// WSL/Docker backend whose cwd is POSIX, so a Windows host path must cross the
+// boundary as bytes just like a remote attachment.
+function attachmentPathNeedsUpload(path: string, backendCwd?: null | string): boolean {
+  return WINDOWS_ABSOLUTE_PATH_RE.test(path.trim()) && POSIX_ABSOLUTE_PATH_RE.test(backendCwd?.trim() || '')
+}
+
 /**
  * Stage one file/image attachment into the session workspace and return the
- * attachment rewritten with the gateway-side ref. Images upload their bytes in
- * remote mode (so vision works) and pass the path locally; non-image files
- * upload bytes remotely and pass the path locally. Throws on failure so callers
- * can surface an error. Shared by submit-time sync, the eager drop-time upload,
- * and the message-edit composer drop — keep them in lockstep.
+ * attachment rewritten with the gateway-side ref. Attachments upload their
+ * bytes for remote gateways and local cross-filesystem backends; otherwise the
+ * gateway receives the shared local path. Throws on failure so callers can
+ * surface an error. Shared by submit-time sync, the eager drop-time upload, and
+ * the message-edit composer drop — keep them in lockstep.
  */
 export async function uploadComposerAttachment(
   attachment: ComposerAttachment,
-  opts: { remote: boolean; requestGateway: GatewayRequest; sessionId: string }
+  opts: { backendCwd?: null | string; remote: boolean; requestGateway: GatewayRequest; sessionId: string }
 ): Promise<ComposerAttachment> {
-  const { remote, requestGateway, sessionId } = opts
+  const { backendCwd, remote, requestGateway, sessionId } = opts
   const path = attachment.path ?? ''
   const label = attachment.label || pathLabel(path)
+  const uploadBytes = remote || attachmentPathNeedsUpload(path, backendCwd)
 
   if (attachment.kind === 'image') {
     let result: ImageAttachResponse
 
-    if (remote) {
+    if (uploadBytes) {
       let payload: Awaited<ReturnType<typeof readImageForRemoteAttach>>
 
       try {
@@ -138,7 +151,7 @@ export async function uploadComposerAttachment(
   // Non-image file.
   let dataUrl: string | null = null
 
-  if (remote) {
+  if (uploadBytes) {
     try {
       dataUrl = await readFileDataUrlForAttach(path)
     } catch (err) {
@@ -317,7 +330,12 @@ export function usePromptActions({
         }
 
         if (attachment.kind === 'image' || attachment.kind === 'file') {
-          const nextAttachment = await uploadComposerAttachment(attachment, { remote, requestGateway, sessionId })
+          const nextAttachment = await uploadComposerAttachment(attachment, {
+            backendCwd: $currentCwd.get(),
+            remote,
+            requestGateway,
+            sessionId
+          })
 
           // Update-only: never resurrect a chip the user removed mid-upload.
           if (updateComposerAttachments) {
@@ -356,7 +374,14 @@ export function usePromptActions({
       try {
         // Update-only: if the user removed the chip while this was uploading,
         // don't resurrect it — just drop the staged result on the floor.
-        updateComposerAttachment(await uploadComposerAttachment(attachment, { remote, requestGateway, sessionId }))
+        updateComposerAttachment(
+          await uploadComposerAttachment(attachment, {
+            backendCwd: $currentCwd.get(),
+            remote,
+            requestGateway,
+            sessionId
+          })
+        )
       } catch (err) {
         // Leave the chip in place so submit-time sync can retry (or the user can
         // remove it) and flag the card; also toast so a hard failure (unreadable

apps/desktop/src/components/assistant-ui/thread/user-edit-composer.tsx

@@ -415,7 +415,7 @@ export const UserEditComposer: FC<UserEditComposerProps> = ({ cwd, gateway, sess
         try {
           const uploaded = await uploadComposerAttachment(
             { detail: path, id: attachmentId(kind, path), kind, label: pathLabel(path), path },
-            { remote, requestGateway, sessionId }
+            { backendCwd: cwd, remote, requestGateway, sessionId }
           )
 
           const ref = attachmentDisplayText(uploaded)