fix(files): answer 499 instead of 500 when a client disconnects mid-serve

The file serve route catches its own errors, so an abort thrown after the
client went away was logged at error and answered 500, bypassing the 499
classification withRouteHandler already applies. Rethrow when the request
signal has aborted, in the outer catch and in the cloud and local read
helpers that log before rethrowing.

Author: waleedlatif1

apps/sim/app/api/files/serve/[...path]/route.test.ts

@@ -34,6 +34,7 @@ import {
   workspaceFileManagerMock,
   workspaceFileManagerMockFns,
 } from '@sim/testing/mocks/workspace-file-manager.mock'
+import { NextRequest } from 'next/server'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { MAX_BUFFERED_TRANSFER_BYTES } from '@/lib/uploads/shared/types'
 
@@ -325,6 +326,24 @@ describe('File Serve API Route', () => {
     expect(serveLogger.error).not.toHaveBeenCalled()
   })
 
+  it('answers 499 without an error log when the client disconnects mid-read', async () => {
+    const controller = new AbortController()
+    mockReadLocalFileWithinLimit.mockImplementation(async () => {
+      controller.abort()
+      throw new Error('Request aborted')
+    })
+
+    const response = await GET(
+      new NextRequest('http://localhost:3000/api/files/serve/workspace/ws/report.md', {
+        signal: controller.signal,
+      }),
+      createRouteContext({ path: ['workspace', 'ws', 'report.md'] })
+    )
+
+    expect(response.status).toBe(499)
+    expect(serveLogger.error).not.toHaveBeenCalled()
+  })
+
   describe('versioned cache lifetime', () => {
     const principal = createExecutorPrincipal({
       subjectUserId: 'test-user-id',

apps/sim/app/api/files/serve/[...path]/route.ts

@@ -389,6 +389,7 @@ export const GET = withRouteHandler(
         request.method === 'HEAD'
       )
     } catch (error) {
+      if (request.signal.aborted) throw error
       if (error instanceof InternalUnauthenticatedError) {
         logger.warn('Unauthorized file access attempt', { error: error.message })
         return NextResponse.json(
@@ -599,6 +600,7 @@ async function handleLocalFile(
       options.ifNoneMatch
     )
   } catch (error) {
+    if (signal?.aborted) throw error
     logServeFailure('Error reading local file:', error)
     throw error
   }
@@ -689,6 +691,7 @@ async function handleCloudProxy(
       options.ifNoneMatch
     )
   } catch (error) {
+    if (signal?.aborted) throw error
     logServeFailure('Error downloading from cloud storage:', error)
     throw error
   }