feat(mentor-workspace): re-scope files from assignment to project for team-wide visibility

- MentorFile.projectId is the new access boundary; mentorAssignmentId stays
  as informational audit FK (nullable).
- uploadFile derives projectId from the assignment; getFiles takes projectId
  directly; deleteFile/addFileComment auth checks any mentor on the project
  OR a project team member.
- HMAC upload token now binds to projectId (in addition to assignmentId).
- promoteFile reads file.projectId directly (no more mentorAssignment null
  navigation).
- Removes 3 placeholder NOT_FOUND guards added in Task 4.

src/app/(applicant)/applicant/mentor/page.tsx

@@ -139,8 +139,9 @@ export default function ApplicantMentorPage() {
       )}
 
       {/* Files */}
-      {primaryAssignment?.id && (
+      {primaryAssignment?.id && projectId && (
         <WorkspaceFilesPanel
+          projectId={projectId}
           mentorAssignmentId={primaryAssignment.id}
           asApplicant
         />

src/app/(mentor)/mentor/workspace/[projectId]/page.tsx

@@ -104,7 +104,10 @@ export default function MentorWorkspaceDetailPage() {
 
         <TabsContent value="files" className="mt-6">
           {assignment ? (
-            <WorkspaceFilesPanel mentorAssignmentId={assignment.id} />
+            <WorkspaceFilesPanel
+              projectId={projectId}
+              mentorAssignmentId={assignment.id}
+            />
           ) : (
             <Card>
               <CardContent className="text-center py-8">
@@ -117,7 +120,7 @@ export default function MentorWorkspaceDetailPage() {
 
         <TabsContent value="promotion" className="mt-6">
           {assignment ? (
-            <FilePromotionPanel mentorAssignmentId={assignment.id} />
+            <FilePromotionPanel projectId={projectId} />
           ) : (
             <Card>
               <CardContent className="text-center py-8">

src/components/mentor/file-promotion-panel.tsx

@@ -17,7 +17,7 @@ import { FileText, Upload, CheckCircle2, ArrowUp } from 'lucide-react'
 import { toast } from 'sonner'
 
 interface FilePromotionPanelProps {
-  mentorAssignmentId: string
+  projectId: string
 }
 
 function formatFileSize(bytes: number): string {
@@ -28,14 +28,14 @@ function formatFileSize(bytes: number): string {
   return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i]
 }
 
-export function FilePromotionPanel({ mentorAssignmentId }: FilePromotionPanelProps) {
+export function FilePromotionPanel({ projectId }: FilePromotionPanelProps) {
   const [selectedSlot, setSelectedSlot] = useState<string>('')
   const utils = trpc.useUtils()
 
   const { data: workspaceFiles = [], isLoading: filesLoading } =
     trpc.mentor.workspaceGetFiles.useQuery(
-      { mentorAssignmentId },
-      { enabled: !!mentorAssignmentId },
+      { projectId },
+      { enabled: !!projectId },
     )
 
   const promoteMutation = trpc.mentor.workspacePromoteFile.useMutation({

src/components/mentor/workspace-files-panel.tsx

@@ -16,6 +16,13 @@ import { FileText, Upload, Download, Trash2, MessageSquare } from 'lucide-react'
 import { formatDistanceToNow } from 'date-fns'
 
 interface Props {
+  /** Project the workspace belongs to — drives file list (project-scoped). */
+  projectId: string
+  /**
+   * One MentorAssignment id on this project — needed only to mint upload tokens
+   * (the token is signed against the assignment + project pair, but the file
+   * itself is project-scoped so co-mentors see it).
+   */
   mentorAssignmentId: string
   /** Set true on the applicant side to label uploads as "Team upload" — purely cosmetic. */
   asApplicant?: boolean
@@ -29,21 +36,21 @@ function formatSize(bytes: number): string {
   return parseFloat((bytes / Math.pow(k, i)).toFixed(1)) + ' ' + sizes[i]
 }
 
-export function WorkspaceFilesPanel({ mentorAssignmentId, asApplicant }: Props) {
+export function WorkspaceFilesPanel({ projectId, mentorAssignmentId, asApplicant }: Props) {
   const utils = trpc.useUtils()
   const inputRef = useRef<HTMLInputElement>(null)
   const [uploading, setUploading] = useState(false)
   const [description, setDescription] = useState('')
 
   const { data: files, isLoading } = trpc.mentor.workspaceGetFiles.useQuery(
-    { mentorAssignmentId },
-    { enabled: !!mentorAssignmentId }
+    { projectId },
+    { enabled: !!projectId }
   )
 
   const presign = trpc.mentor.workspaceGetUploadUrl.useMutation()
   const recordUpload = trpc.mentor.workspaceUploadFile.useMutation({
     onSuccess: () => {
-      utils.mentor.workspaceGetFiles.invalidate({ mentorAssignmentId })
+      utils.mentor.workspaceGetFiles.invalidate({ projectId })
       setDescription('')
       toast.success('File uploaded')
     },
@@ -51,7 +58,7 @@ export function WorkspaceFilesPanel({ mentorAssignmentId, asApplicant }: Props)
   const downloadMutation = trpc.mentor.workspaceGetFileDownloadUrl.useMutation()
   const deleteMutation = trpc.mentor.workspaceDeleteFile.useMutation({
     onSuccess: () => {
-      utils.mentor.workspaceGetFiles.invalidate({ mentorAssignmentId })
+      utils.mentor.workspaceGetFiles.invalidate({ projectId })
       toast.success('File deleted')
     },
     onError: (e) => toast.error(e.message),

src/lib/mentor-upload-token.ts

@@ -2,6 +2,13 @@ import { createHmac, timingSafeEqual } from 'crypto'
 
 export type MentorUploadPayload = {
   mentorAssignmentId: string
+  /**
+   * Project the upload belongs to. Bound at token-issue time so the file's
+   * project scope can't be tampered with separately from the assignment id.
+   * Required (no legacy fallback) — tokens live <1h, so any in-flight tokens
+   * issued before this field was added expire on their own.
+   */
+  projectId: string
   uploaderUserId: string
   fileName: string
   mimeType: string
@@ -47,5 +54,8 @@ export function verifyMentorUploadToken(token: string): MentorUploadPayload {
   if (typeof payload.exp !== 'number' || payload.exp < Math.floor(Date.now() / 1000)) {
     throw new Error('Invalid mentor upload token: expired')
   }
+  if (typeof payload.projectId !== 'string' || payload.projectId.length === 0) {
+    throw new Error('Invalid mentor upload token: missing projectId')
+  }
   return payload
 }

src/server/routers/mentor.ts

@@ -67,6 +67,42 @@ async function assertWorkspaceAccess(
   throw new TRPCError({ code: 'FORBIDDEN', message: 'You are not a member of this workspace' })
 }
 
+/**
+ * Project-scoped workspace access check (PR8 multi-mentor).
+ *
+ * Allowed when the user is either:
+ *   1) currently assigned as a mentor on this project (droppedAt = null), OR
+ *   2) a team member of the project.
+ *
+ * Also requires at least one active mentor assignment for the project with
+ * workspaceEnabled = true — meaning the project actually has a live workspace.
+ * Throws TRPCError on failure. Returns nothing on success.
+ */
+async function assertProjectWorkspaceAccess(
+  prisma: PrismaClient,
+  userId: string,
+  projectId: string,
+): Promise<void> {
+  const liveMentorAssignment = await prisma.mentorAssignment.findFirst({
+    where: { projectId, droppedAt: null, workspaceEnabled: true },
+    select: { id: true },
+  })
+  if (!liveMentorAssignment) {
+    throw new TRPCError({ code: 'FORBIDDEN', message: 'Workspace is not enabled' })
+  }
+  const mentorOnProject = await prisma.mentorAssignment.findFirst({
+    where: { projectId, mentorId: userId, droppedAt: null },
+    select: { id: true },
+  })
+  if (mentorOnProject) return
+  const teamMembership = await prisma.teamMember.findFirst({
+    where: { projectId, userId },
+    select: { id: true },
+  })
+  if (teamMembership) return
+  throw new TRPCError({ code: 'FORBIDDEN', message: 'You are not a member of this workspace' })
+}
+
 export const mentorRouter = router({
   /**
    * Get AI-suggested mentor matches for a project
@@ -2127,6 +2163,7 @@ export const mentorRouter = router({
       const exp = Math.floor(Date.now() / 1000) + 3600
       const uploadToken = signMentorUploadToken({
         mentorAssignmentId: assignment.id,
+        projectId: assignment.projectId,
         uploaderUserId: ctx.user.id,
         fileName: input.fileName,
         mimeType: input.mimeType,
@@ -2183,14 +2220,17 @@ export const mentorRouter = router({
     }),
 
   /**
-   * List files in a workspace. Authorized for the assigned mentor or any
-   * project team member.
+   * List files in a project's mentor workspace. Authorized for any mentor
+   * currently assigned to the project, or any team member of the project.
+   *
+   * Project-scoped (PR8): all co-mentors share one file list, and files
+   * survive even when an originating assignment is later dropped.
    */
   workspaceGetFiles: protectedProcedure
-    .input(z.object({ mentorAssignmentId: z.string() }))
+    .input(z.object({ projectId: z.string() }))
     .query(async ({ ctx, input }) => {
-      await assertWorkspaceAccess(ctx.prisma, ctx.user.id, input.mentorAssignmentId)
-      return workspaceGetFilesService(input.mentorAssignmentId, ctx.prisma)
+      await assertProjectWorkspaceAccess(ctx.prisma, ctx.user.id, input.projectId)
+      return workspaceGetFilesService(input.projectId, ctx.prisma)
     }),
 
   /**
@@ -2201,37 +2241,29 @@ export const mentorRouter = router({
     .mutation(async ({ ctx, input }) => {
       const file = await ctx.prisma.mentorFile.findUnique({
         where: { id: input.mentorFileId },
-        select: { bucket: true, objectKey: true, fileName: true, mentorAssignmentId: true },
+        select: { bucket: true, objectKey: true, fileName: true, projectId: true },
       })
       if (!file) throw new TRPCError({ code: 'NOT_FOUND', message: 'File not found' })
-      // TODO(PR8 Task 5): re-scope workspace access from assignment to project
-      // so files whose original assignment was dropped (mentorAssignmentId =
-      // null) remain accessible by the team.
-      if (!file.mentorAssignmentId) {
-        throw new TRPCError({ code: 'NOT_FOUND', message: 'Orphaned workspace file' })
-      }
-      await assertWorkspaceAccess(ctx.prisma, ctx.user.id, file.mentorAssignmentId)
+      await assertProjectWorkspaceAccess(ctx.prisma, ctx.user.id, file.projectId)
       const url = await getPresignedUrl(file.bucket, file.objectKey, 'GET', 900,
         { downloadFileName: file.fileName })
       return { url }
     }),
 
   /**
-   * Delete a workspace file (uploader or assigned mentor only).
+   * Delete a workspace file. Authorized for the uploader, any mentor
+   * currently assigned to the file's project, or any team member of the
+   * file's project. Final auth check lives in the service.
    */
   workspaceDeleteFile: protectedProcedure
     .input(z.object({ mentorFileId: z.string() }))
     .mutation(async ({ ctx, input }) => {
       const file = await ctx.prisma.mentorFile.findUnique({
         where: { id: input.mentorFileId },
-        select: { mentorAssignmentId: true },
+        select: { projectId: true },
       })
       if (!file) throw new TRPCError({ code: 'NOT_FOUND', message: 'File not found' })
-      // TODO(PR8 Task 5): re-scope workspace access from assignment to project.
-      if (!file.mentorAssignmentId) {
-        throw new TRPCError({ code: 'NOT_FOUND', message: 'Orphaned workspace file' })
-      }
-      await assertWorkspaceAccess(ctx.prisma, ctx.user.id, file.mentorAssignmentId)
+      await assertProjectWorkspaceAccess(ctx.prisma, ctx.user.id, file.projectId)
       try {
         await workspaceDeleteFileService(
           { mentorFileId: input.mentorFileId, userId: ctx.user.id },
@@ -2261,16 +2293,12 @@ export const mentorRouter = router({
     .mutation(async ({ ctx, input }) => {
       const file = await ctx.prisma.mentorFile.findUnique({
         where: { id: input.mentorFileId },
-        select: { mentorAssignmentId: true },
+        select: { projectId: true },
       })
       if (!file) {
         throw new TRPCError({ code: 'NOT_FOUND', message: 'File not found' })
       }
-      // TODO(PR8 Task 5): re-scope workspace access from assignment to project.
-      if (!file.mentorAssignmentId) {
-        throw new TRPCError({ code: 'NOT_FOUND', message: 'Orphaned workspace file' })
-      }
-      await assertWorkspaceAccess(ctx.prisma, ctx.user.id, file.mentorAssignmentId)
+      await assertProjectWorkspaceAccess(ctx.prisma, ctx.user.id, file.projectId)
       return workspaceAddFileComment(
         {
           mentorFileId: input.mentorFileId,

src/server/services/mentor-workspace.ts

@@ -152,6 +152,11 @@ export async function markRead(
 
 /**
  * Record a file upload in a workspace.
+ *
+ * `workspaceId` is the originating MentorAssignment id (kept on the row as an
+ * audit-trail FK). We derive the project id from that assignment so the file
+ * is bound to the project — meaning any co-mentor on the project can see/use
+ * it, and the row survives if this particular assignment is later dropped.
  */
 export async function uploadFile(
   params: {
@@ -180,6 +185,7 @@ export async function uploadFile(
 
   return prisma.mentorFile.create({
     data: {
+      projectId: assignment.projectId,
       mentorAssignmentId: params.workspaceId,
       uploadedByUserId: params.uploadedByUserId,
       fileName: params.fileName,
@@ -238,9 +244,6 @@ export async function promoteFile(
   try {
     const file = await prisma.mentorFile.findUnique({
       where: { id: params.mentorFileId },
-      include: {
-        mentorAssignment: { select: { projectId: true } },
-      },
     })
 
     if (!file) {
@@ -265,7 +268,7 @@ export async function promoteFile(
       // Create promotion event
       await tx.submissionPromotionEvent.create({
         data: {
-          projectId: file.mentorAssignment.projectId,
+          projectId: file.projectId,
           roundId: params.roundId,
           slotKey: params.slotKey,
           sourceType: 'MENTOR_FILE',
@@ -281,7 +284,7 @@ export async function promoteFile(
           entityId: params.mentorFileId,
           actorId: params.promotedById,
           detailsJson: {
-            projectId: file.mentorAssignment.projectId,
+            projectId: file.projectId,
             roundId: params.roundId,
             slotKey: params.slotKey,
             fileName: file.fileName,
@@ -297,7 +300,7 @@ export async function promoteFile(
         entityType: 'MentorFile',
         entityId: params.mentorFileId,
         detailsJson: {
-          projectId: file.mentorAssignment.projectId,
+          projectId: file.projectId,
           slotKey: params.slotKey,
         },
       })
@@ -314,14 +317,17 @@ export async function promoteFile(
 }
 
 /**
- * List files for a workspace, newest first, with comment counts and uploader.
+ * List files for a project, newest first, with comment counts and uploader.
+ * Project-scoped: every mentor assigned to the project (and every team member)
+ * sees the same file list, even if some files were uploaded under a now-dropped
+ * assignment.
  */
 export async function getFiles(
-  workspaceId: string,
+  projectId: string,
   prisma: PrismaClient,
 ) {
   return prisma.mentorFile.findMany({
-    where: { mentorAssignmentId: workspaceId },
+    where: { projectId },
     orderBy: { createdAt: 'desc' },
     include: {
       uploadedBy: { select: { id: true, name: true, email: true } },
@@ -331,8 +337,10 @@ export async function getFiles(
 }
 
 /**
- * Delete a file. Caller must be either the uploader OR the assigned mentor.
- * Removes the MinIO object and the DB row + cascade-deletes comments.
+ * Delete a file. Caller must be either the uploader, OR any mentor currently
+ * assigned (not dropped) to the file's project, OR a team member of the
+ * file's project. Removes the MinIO object and the DB row + cascade-deletes
+ * comments.
  */
 export async function deleteFile(
   params: { mentorFileId: string; userId: string },
@@ -341,13 +349,30 @@ export async function deleteFile(
 ): Promise<void> {
   const file = await prisma.mentorFile.findUnique({
     where: { id: params.mentorFileId },
-    include: { mentorAssignment: { select: { mentorId: true } } },
   })
   if (!file) throw new Error('File not found')
   const isUploader = file.uploadedByUserId === params.userId
-  const isMentor = file.mentorAssignment.mentorId === params.userId
-  if (!isUploader && !isMentor) {
-    throw new Error('Only the uploader or the assigned mentor can delete this file')
+  let isAuthorized = isUploader
+  if (!isAuthorized) {
+    const mentorAssignment = await prisma.mentorAssignment.findFirst({
+      where: { projectId: file.projectId, mentorId: params.userId, droppedAt: null },
+      select: { id: true },
+    })
+    if (mentorAssignment) {
+      isAuthorized = true
+    }
+  }
+  if (!isAuthorized) {
+    const teamMembership = await prisma.teamMember.findFirst({
+      where: { projectId: file.projectId, userId: params.userId },
+      select: { id: true },
+    })
+    if (teamMembership) {
+      isAuthorized = true
+    }
+  }
+  if (!isAuthorized) {
+    throw new Error('Only the uploader, an assigned mentor, or a team member can delete this file')
   }
   try {
     await removeStorageObject(file.bucket, file.objectKey)