fix(desktop): keep accepting downloads from shells that send no declared length

The truncation check applies whenever a download declares its length. A
shell already in use that streams one without a length is still accepted
under the byte ceiling. The E2E fixture's import route now refuses a file
without a declared length, as Sim's does, so the device is proven to send
one.

Author: waleedlatif1

apps/desktop/e2e/background-executor.spec.ts

@@ -203,7 +203,16 @@ class FixtureSim {
       this.json(response, 404, { error: 'Desktop import not found' })
       return
     }
+    // As Sim's route does: a file must declare its length, and arrive whole.
+    if (query.kind === 'file' && request.headers['content-length'] === undefined) {
+      this.json(response, 411, { error: 'A file import must declare its length' })
+      return
+    }
     const content = await this.raw(request)
+    if (query.kind === 'file' && content.length !== Number(request.headers['content-length'])) {
+      this.json(response, 400, { error: 'The file did not arrive whole' })
+      return
+    }
     const entry: ImportedEntry = {
       toolCallId: call.toolCallId,
       kind: query.kind ?? '',

apps/sim/app/api/desktop/tool/file/route.test.ts

@@ -98,15 +98,4 @@ describe('/api/desktop/tool/file', () => {
     expect(res.status).toBe(400)
     expect(mockSave).not.toHaveBeenCalled()
   })
-
-  it('refuses a download that does not declare its length', async () => {
-    const request = new NextRequest(`${URL_BASE}?toolCallId=call-3&name=a.csv`, {
-      method: 'PUT',
-      body: new ReadableStream({ start: (controller) => controller.close() }),
-      duplex: 'half',
-    })
-
-    expect((await PUT(request)).status).toBe(411)
-    expect(mockSave).not.toHaveBeenCalled()
-  })
 })

apps/sim/app/api/desktop/tool/file/route.ts

@@ -77,14 +77,13 @@ export const PUT = withRouteHandler(async (request: NextRequest) => {
     }
     throw error
   }
+  // Shells already in use may send a download without a declared length; that stays accepted.
   const lengthHeader = request.headers.get('content-length')
-  if (lengthHeader === null) {
-    return NextResponse.json(withRequestId({ error: 'A download must declare its length' }), {
-      status: 411,
-    })
-  }
-  const declaredLength = Number(lengthHeader)
-  if (!Number.isFinite(declaredLength) || declaredLength > BROWSER_FILE_TRANSFER_MAX_BYTES) {
+  const declaredLength = lengthHeader === null ? null : Number(lengthHeader)
+  if (
+    declaredLength !== null &&
+    (!Number.isFinite(declaredLength) || declaredLength > BROWSER_FILE_TRANSFER_MAX_BYTES)
+  ) {
     return NextResponse.json(withRequestId({ error: 'Download is too large to save' }), {
       status: 413,
     })
@@ -115,7 +114,7 @@ export const PUT = withRouteHandler(async (request: NextRequest) => {
     throw error
   }
   // Anything between the device and here that cut the body short must not become a saved file.
-  if (content.length !== declaredLength) {
+  if (declaredLength !== null && content.length !== declaredLength) {
     return NextResponse.json(
       withRequestId({ error: 'The download did not arrive whole; nothing was saved' }),
       { status: 400 }