fix(files): read the root's folder stats when parentId is omitted

Zod 4's `.default()` returns its value without running the schema's
transform, so an omitted `parentId` reached the use case as the literal
`root`, an unknown folder id, and the endpoint answered no folders.
`.prefault('root')` parses the default through the transform to `null`.

The legacy-cursor integration test now ends its first page inside the
millisecond tie, and spells the cursor in SQL: the driver parses a raw
`timestamp` as local time, which had shifted the cursor past the tie.

Author: waleedlatif1

apps/sim/app/api/workspaces/[id]/files/folder-stats/route.test.ts

@@ -0,0 +1,41 @@
+import { authMockFns } from '@sim/testing'
+import { createRouteContext } from '@sim/testing/helpers/http'
+import { createMockRequest } from '@sim/testing/mocks/request.mock'
+import {
+  workspaceFilesListMock,
+  workspaceFilesListMockFns,
+} from '@sim/testing/mocks/workspace-files-list.mock'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('@/lib/workspace-files/application/list-workspace-files', () => workspaceFilesListMock)
+
+import { GET } from '@/app/api/workspaces/[id]/files/folder-stats/route'
+
+const WORKSPACE_ID = 'workspace-1'
+const stats = workspaceFilesListMockFns.mockGetWorkspaceFileFolderStats
+
+describe('GET /api/workspaces/[id]/files/folder-stats', () => {
+  beforeEach(() => {
+    authMockFns.mockGetSession.mockResolvedValue({
+      user: { id: 'user-1', name: 'Test User', email: 'test@sim.ai' },
+      session: { id: 'session-1' },
+    })
+    stats.mockResolvedValue({ folders: [] })
+  })
+
+  it.each([
+    ['omitted', ''],
+    ['root', '?parentId=root'],
+  ])('reads the root children when parentId is %s', async (_label, query) => {
+    const response = await GET(
+      createMockRequest({
+        method: 'GET',
+        url: `/api/workspaces/${WORKSPACE_ID}/files/folder-stats${query}`,
+      }),
+      createRouteContext({ id: WORKSPACE_ID })
+    )
+
+    expect(response.status).toBe(200)
+    expect(stats.mock.calls[0][0].input).toEqual({ workspaceId: WORKSPACE_ID, parentId: null })
+  })
+})

apps/sim/lib/api/contracts/workspace-files.ts

@@ -308,7 +308,7 @@ export const lookupWorkspaceFilesContract = defineRouteContract({
 
 const workspaceFileFolderStatsQuerySchema = z.object({
   /** The folder whose child folders to report: `root` (default) or a folder id. */
-  parentId: workspaceFileFolderFilterSchema.default('root'),
+  parentId: workspaceFileFolderFilterSchema.prefault('root'),
 })
 
 const workspaceFileFolderStatsResponseSchema = workspaceFileSuccessSchema.extend({

apps/sim/lib/workspace-files/__integration__/file-listing.integration.ts

@@ -277,17 +277,21 @@ describe('bounded workspace file reads in PostgreSQL', () => {
     )
 
     it('finishes a walk begun under millisecond-truncated ordering without skipping or repeating', async () => {
-      const legacy = await db.execute<{ id: string; uploaded_at: Date }>(sql`
-        SELECT id, uploaded_at FROM ${workspaceFiles}
+      // The millisecond cursor a legacy page minted, spelled in SQL: a raw `timestamp` read back
+      // through the driver is parsed as local time.
+      const legacy = await db.execute<{ id: string; cursor: string }>(sql`
+        SELECT id, to_char(uploaded_at, 'YYYY-MM-DD"T"HH24:MI:SS.MS"Z"') AS cursor
+        FROM ${workspaceFiles}
         WHERE workspace_id = ${workspaceId} AND context = 'workspace' AND deleted_at IS NULL
         ORDER BY date_trunc('milliseconds', uploaded_at), id`)
       const legacyOrder = legacy.map((row) => row.id)
-      const firstPage = legacy.slice(0, 2)
-      const last = firstPage[1]
-      const resumed = await walk('uploadedAt', 'asc', [
-        new Date(last.uploaded_at).toISOString(),
-        last.id,
-      ])
+      // End the legacy page on wf_a, first of the four rows sharing one millisecond, so the walk
+      // resumes inside the tie, where raw and truncated ordering disagree.
+      const cut = legacy.findIndex((row) => row.id.startsWith('wf_a_')) + 1
+      const firstPage = legacy.slice(0, cut)
+      const last = firstPage[firstPage.length - 1]
+      expect(legacy[cut].cursor).toBe(last.cursor)
+      const resumed = await walk('uploadedAt', 'asc', [last.cursor, last.id])
       expect([...firstPage.map((row) => row.id), ...resumed]).toEqual(legacyOrder)
     })
   })