merge: PR8 Task 8 — admin multi-mentor UI + change-request inbox

src/app/(admin)/admin/projects/[id]/mentor/page.tsx

@@ -18,6 +18,8 @@ import { Skeleton } from '@/components/ui/skeleton'
 import { Avatar, AvatarFallback } from '@/components/ui/avatar'
 import { Progress } from '@/components/ui/progress'
 import { Input } from '@/components/ui/input'
+import { Textarea } from '@/components/ui/textarea'
+import { Label } from '@/components/ui/label'
 import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs'
 import {
   Table,
@@ -27,15 +29,35 @@ import {
   TableHeader,
   TableRow,
 } from '@/components/ui/table'
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from '@/components/ui/dialog'
+import {
+  AlertDialog,
+  AlertDialogAction,
+  AlertDialogCancel,
+  AlertDialogContent,
+  AlertDialogDescription,
+  AlertDialogFooter,
+  AlertDialogHeader,
+  AlertDialogTitle,
+} from '@/components/ui/alert-dialog'
 import {
   AlertTriangle,
   ArrowLeft,
   Bot,
   Check,
+  Inbox,
   Loader2,
   Search,
   Sparkles,
   Users,
+  UserPlus,
 } from 'lucide-react'
 import { getInitials, formatEnumLabel } from '@/lib/utils'
 
@@ -48,14 +70,31 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
   const utils = trpc.useUtils()
   const [search, setSearch] = useState('')
   const [pendingMentorId, setPendingMentorId] = useState<string | null>(null)
+  const [unassignTarget, setUnassignTarget] = useState<{
+    assignmentId: string
+    mentorName: string
+  } | null>(null)
 
   const { data: project, isLoading: projectLoading } = trpc.project.get.useQuery({ id: projectId })
 
-  const { data: candidatesData, isLoading: candidatesLoading } =
+  // Already-assigned mentors (full list). Project.get spreads the underlying
-    trpc.mentor.getCandidates.useQuery(
+  // `mentorAssignments` relation so we can read it directly.
-      { projectId },
+  const assignedMentorAssignments = useMemo(() => {
-      { enabled: !!project && !project.mentorAssignment },
+    if (!project) return []
+    // The Prisma relation is included via `...project` spread; type comes
+    // through the tRPC client.
+    type Assignment = NonNullable<typeof project>['mentorAssignments'][number]
+    return ((project as unknown as { mentorAssignments?: Assignment[] }).mentorAssignments ?? []).filter(
+      (a) => !a.droppedAt,
     )
+  }, [project])
+  const assignedMentorIds = useMemo(
+    () => new Set(assignedMentorAssignments.map((a) => a.mentorId)),
+    [assignedMentorAssignments],
+  )
+
+  const { data: candidatesData, isLoading: candidatesLoading } =
+    trpc.mentor.getCandidates.useQuery({ projectId }, { enabled: !!project })
 
   const {
     data: suggestionsData,
@@ -63,12 +102,12 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
     refetch: refetchSuggestions,
   } = trpc.mentor.getSuggestions.useQuery(
     { projectId, limit: 5 },
-    { enabled: !!project && !project.mentorAssignment },
+    { enabled: !!project },
   )
 
   const assignMutation = trpc.mentor.assign.useMutation({
     onSuccess: () => {
-      toast.success('Mentor assigned')
+      toast.success('Mentor added')
       utils.project.get.invalidate({ id: projectId })
       utils.mentor.getCandidates.invalidate({ projectId })
       utils.mentor.getSuggestions.invalidate({ projectId })
@@ -86,21 +125,31 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
       utils.project.get.invalidate({ id: projectId })
       utils.mentor.getCandidates.invalidate({ projectId })
       utils.mentor.getSuggestions.invalidate({ projectId })
+      setUnassignTarget(null)
+    },
+    onError: (err) => {
+      toast.error(err.message)
+      setUnassignTarget(null)
     },
-    onError: (err) => toast.error(err.message),
   })
 
   const filteredCandidates = useMemo(() => {
     if (!candidatesData) return []
+    const base = candidatesData.candidates.filter((c) => !assignedMentorIds.has(c.id))
     const q = search.trim().toLowerCase()
-    if (!q) return candidatesData.candidates
+    if (!q) return base
-    return candidatesData.candidates.filter((c) => {
+    return base.filter((c) => {
       const hay = [c.name ?? '', c.email, ...(c.expertiseTags ?? []), c.country ?? '']
         .join(' ')
         .toLowerCase()
       return hay.includes(q)
     })
-  }, [candidatesData, search])
+  }, [candidatesData, search, assignedMentorIds])
+
+  const filteredSuggestions = useMemo(() => {
+    if (!suggestionsData) return []
+    return suggestionsData.suggestions.filter((s) => !assignedMentorIds.has(s.mentorId))
+  }, [suggestionsData, assignedMentorIds])
 
   if (projectLoading) return <MentorAssignmentSkeleton />
   if (!project) {
@@ -113,7 +162,6 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
     )
   }
 
-  const hasMentor = !!project.mentorAssignment
   const teamSize = project.teamMembers?.length ?? 0
   const aiSource = suggestionsData?.source ?? 'ai'
 
@@ -206,80 +254,112 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
         </CardContent>
       </Card>
 
+      {/* ─── Pending Change Requests ─── */}
+      <PendingChangeRequestsPanel projectId={projectId} />
+
       {/* ─── Currently Assigned ─── */}
       <Card>
         <CardHeader>
           <CardTitle className="text-lg">Currently Assigned</CardTitle>
+          <CardDescription>
+            {assignedMentorAssignments.length === 0
+              ? 'No mentors assigned yet'
+              : `${assignedMentorAssignments.length} mentor${
+                  assignedMentorAssignments.length === 1 ? '' : 's'
+                } on this team`}
+          </CardDescription>
         </CardHeader>
         <CardContent>
-          {hasMentor ? (
+          {assignedMentorAssignments.length === 0 ? (
-            <div className="flex items-center justify-between">
+            <div className="rounded-md border border-dashed py-8 text-center">
-              <div className="flex items-center gap-4">
+              <Users className="text-muted-foreground mx-auto mb-2 h-8 w-8" />
+              <p className="text-muted-foreground text-sm">
+                No mentors assigned yet — add one below.
+              </p>
+            </div>
+          ) : (
+            <ul className="divide-y">
+              {assignedMentorAssignments.map((a) => {
+                const m = a.mentor
+                const tags = m.expertiseTags ?? []
+                return (
+                  <li
+                    key={a.id}
+                    className="flex items-start justify-between gap-4 py-4 first:pt-0 last:pb-0"
+                  >
+                    <div className="flex flex-1 items-start gap-4">
                       <Avatar className="h-12 w-12">
                         <AvatarFallback>
-                    {getInitials(
+                          {getInitials(m.name || m.email)}
-                      project.mentorAssignment!.mentor.name ||
-                        project.mentorAssignment!.mentor.email,
-                    )}
                         </AvatarFallback>
                       </Avatar>
-                <div>
+                      <div className="min-w-0 flex-1">
                         <Link
-                    href={`/admin/mentors/${project.mentorAssignment!.mentor.id}`}
+                          href={`/admin/mentors/${m.id}`}
                           className="font-medium hover:underline"
                         >
-                    {project.mentorAssignment!.mentor.name || 'Unnamed'}
+                          {m.name || 'Unnamed'}
                         </Link>
-                  <p className="text-muted-foreground text-sm">
+                        <p className="text-muted-foreground text-sm">{m.email}</p>
-                    {project.mentorAssignment!.mentor.email}
+                        {tags.length > 0 && (
-                  </p>
-                  {project.mentorAssignment!.mentor.expertiseTags &&
-                    project.mentorAssignment!.mentor.expertiseTags.length > 0 && (
                           <div className="mt-1 flex flex-wrap gap-1">
-                        {project.mentorAssignment!.mentor.expertiseTags
+                            {tags.slice(0, 5).map((tag: string) => (
-                          .slice(0, 5)
-                          .map((tag: string) => (
                               <Badge key={tag} variant="secondary" className="text-xs">
                                 {tag}
                               </Badge>
                             ))}
+                            {tags.length > 5 && (
+                              <Badge variant="outline" className="text-xs">
+                                +{tags.length - 5}
+                              </Badge>
+                            )}
                           </div>
                         )}
+                        <p className="text-muted-foreground mt-2 text-xs">
+                          Assigned{' '}
+                          {new Date(a.assignedAt).toLocaleDateString(undefined, {
+                            year: 'numeric',
+                            month: 'short',
+                            day: 'numeric',
+                          })}
+                        </p>
                       </div>
                     </div>
                     <div className="flex flex-col items-end gap-2">
                       <Badge variant="outline" className="text-xs">
-                  {project.mentorAssignment!.method.replace(/_/g, ' ')}
+                        {a.method.replace(/_/g, ' ')}
                       </Badge>
                       <Button
-                  variant="destructive"
+                        variant="outline"
                         size="sm"
-                  onClick={() => unassignMutation.mutate({ projectId })}
+                        onClick={() =>
+                          setUnassignTarget({
+                            assignmentId: a.id,
+                            mentorName: m.name || m.email,
+                          })
+                        }
                         disabled={unassignMutation.isPending}
                       >
-                  {unassignMutation.isPending ? (
+                        Unassign
-                    <Loader2 className="h-4 w-4 animate-spin" />
-                  ) : (
-                    'Unassign'
-                  )}
                       </Button>
                     </div>
-            </div>
+                  </li>
-          ) : (
+                )
-            <p className="text-muted-foreground text-sm">
+              })}
-              No mentor assigned yet — pick one below.
+            </ul>
-            </p>
           )}
         </CardContent>
       </Card>
 
-      {/* ─── Pick a Mentor ─── */}
+      {/* ─── Add a Mentor ─── */}
-      {!hasMentor && (
       <Card>
         <CardHeader>
-            <CardTitle className="text-lg">Pick a Mentor</CardTitle>
+          <CardTitle className="text-lg flex items-center gap-2">
+            <UserPlus className="h-5 w-5" />
+            Add a Mentor
+          </CardTitle>
           <CardDescription>
-              Browse all eligible mentors or use AI to surface the best fits.
+            Stack additional mentors on this team. Browse all eligible mentors or use AI to surface the best fits.
           </CardDescription>
         </CardHeader>
         <CardContent>
@@ -311,7 +391,9 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
                 </div>
               ) : filteredCandidates.length === 0 ? (
                 <div className="text-muted-foreground py-8 text-center text-sm">
-                    No matching mentors. Try a different search.
+                  {assignedMentorIds.size > 0 && search.trim() === ''
+                    ? 'All eligible mentors are already assigned.'
+                    : 'No matching mentors. Try a different search.'}
                 </div>
               ) : (
                 <div className="overflow-hidden rounded-md border">
@@ -376,7 +458,7 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
                                 <Loader2 className="h-4 w-4 animate-spin" />
                               ) : (
                                 <>
-                                    <Check className="mr-1 h-3.5 w-3.5" /> Assign
+                                  <Check className="mr-1 h-3.5 w-3.5" /> Add
                                 </>
                               )}
                             </Button>
@@ -422,13 +504,15 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
                     <Skeleton key={i} className="h-24 w-full" />
                   ))}
                 </div>
-                ) : !suggestionsData || suggestionsData.suggestions.length === 0 ? (
+              ) : filteredSuggestions.length === 0 ? (
                 <p className="text-muted-foreground py-8 text-center text-sm">
-                    No suggestions available.
+                  {assignedMentorIds.size > 0
+                    ? 'All top suggestions are already assigned.'
+                    : 'No suggestions available.'}
                 </p>
               ) : (
                 <div className="space-y-3">
-                    {suggestionsData.suggestions.map((s, i) => (
+                  {filteredSuggestions.map((s, i) => (
                     <div
                       key={s.mentorId}
                       className="flex items-start justify-between rounded-md border p-4"
@@ -503,7 +587,7 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
                           <Loader2 className="h-4 w-4 animate-spin" />
                         ) : (
                           <>
-                              <Check className="mr-1 h-3.5 w-3.5" /> Assign
+                            <Check className="mr-1 h-3.5 w-3.5" /> Add
                           </>
                         )}
                       </Button>
@@ -515,8 +599,284 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
           </Tabs>
         </CardContent>
       </Card>
+
+      {/* ─── Unassign confirm ─── */}
+      <AlertDialog
+        open={!!unassignTarget}
+        onOpenChange={(open) => {
+          if (!open) setUnassignTarget(null)
+        }}
+      >
+        <AlertDialogContent>
+          <AlertDialogHeader>
+            <AlertDialogTitle>Unassign mentor?</AlertDialogTitle>
+            <AlertDialogDescription>
+              {unassignTarget
+                ? `Remove ${unassignTarget.mentorName} from this team? Other co-mentors will remain.`
+                : ''}
+            </AlertDialogDescription>
+          </AlertDialogHeader>
+          <AlertDialogFooter>
+            <AlertDialogCancel disabled={unassignMutation.isPending}>
+              Cancel
+            </AlertDialogCancel>
+            <AlertDialogAction
+              onClick={(e) => {
+                e.preventDefault()
+                if (!unassignTarget) return
+                unassignMutation.mutate({ assignmentId: unassignTarget.assignmentId })
+              }}
+              disabled={unassignMutation.isPending}
+            >
+              {unassignMutation.isPending ? (
+                <Loader2 className="h-4 w-4 animate-spin" />
+              ) : (
+                'Unassign'
+              )}
+            </AlertDialogAction>
+          </AlertDialogFooter>
+        </AlertDialogContent>
+      </AlertDialog>
+    </div>
+  )
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Pending Change Requests panel
+// ─────────────────────────────────────────────────────────────────────────────
+
+function PendingChangeRequestsPanel({ projectId }: { projectId: string }) {
+  const utils = trpc.useUtils()
+  const { data: requests, isLoading } = trpc.mentor.listChangeRequests.useQuery({
+    projectId,
+    status: 'PENDING',
+  })
+
+  const [resolveTarget, setResolveTarget] = useState<{
+    id: string
+    status: 'RESOLVED' | 'DISMISSED'
+    requesterName: string
+  } | null>(null)
+  const [resolutionNote, setResolutionNote] = useState('')
+
+  const resolveMutation = trpc.mentor.resolveChangeRequest.useMutation({
+    onSuccess: (_, variables) => {
+      toast.success(
+        `Request marked ${variables.status === 'RESOLVED' ? 'resolved' : 'dismissed'}`,
+      )
+      utils.mentor.listChangeRequests.invalidate()
+      setResolveTarget(null)
+      setResolutionNote('')
+    },
+    onError: (err) => toast.error(err.message),
+  })
+
+  if (isLoading) {
+    return (
+      <Card>
+        <CardHeader>
+          <CardTitle className="text-lg flex items-center gap-2">
+            <Inbox className="h-5 w-5" />
+            Pending change requests
+          </CardTitle>
+        </CardHeader>
+        <CardContent>
+          <Skeleton className="h-24 w-full" />
+        </CardContent>
+      </Card>
+    )
+  }
+
+  if (!requests || requests.length === 0) {
+    return null
+  }
+
+  return (
+    <>
+      <Card className="border-amber-300 dark:border-amber-700">
+        <CardHeader>
+          <CardTitle className="text-lg flex items-center gap-2">
+            <Inbox className="h-5 w-5 text-amber-600" />
+            Pending change requests
+            <Badge variant="secondary" className="ml-1">
+              {requests.length}
+            </Badge>
+          </CardTitle>
+          <CardDescription>
+            Team members or mentors have asked admin to change a mentor on this team.
+          </CardDescription>
+        </CardHeader>
+        <CardContent>
+          <ul className="space-y-3">
+            {requests.map((r) => (
+              <ChangeRequestRow
+                key={r.id}
+                request={r}
+                onResolve={(status) =>
+                  setResolveTarget({
+                    id: r.id,
+                    status,
+                    requesterName:
+                      r.requestedBy?.name ?? r.requestedBy?.email ?? 'Unknown',
+                  })
+                }
+              />
+            ))}
+          </ul>
+        </CardContent>
+      </Card>
+
+      <Dialog
+        open={!!resolveTarget}
+        onOpenChange={(open) => {
+          if (!open) {
+            setResolveTarget(null)
+            setResolutionNote('')
+          }
+        }}
+      >
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>
+              {resolveTarget?.status === 'RESOLVED'
+                ? 'Mark request resolved'
+                : 'Dismiss request'}
+            </DialogTitle>
+            <DialogDescription>
+              {resolveTarget?.status === 'RESOLVED'
+                ? `You've taken action on the request from ${resolveTarget?.requesterName}. Optionally add a note explaining what was done.`
+                : `Close the request from ${resolveTarget?.requesterName} without action. Optionally add a note explaining why.`}
+            </DialogDescription>
+          </DialogHeader>
+          <div className="space-y-2">
+            <Label htmlFor="resolution-note">Resolution note (optional)</Label>
+            <Textarea
+              id="resolution-note"
+              value={resolutionNote}
+              onChange={(e) => setResolutionNote(e.target.value)}
+              placeholder="e.g. Replaced Jane with John based on expertise mismatch."
+              rows={4}
+              maxLength={2000}
+            />
+          </div>
+          <DialogFooter>
+            <Button
+              variant="outline"
+              onClick={() => {
+                setResolveTarget(null)
+                setResolutionNote('')
+              }}
+              disabled={resolveMutation.isPending}
+            >
+              Cancel
+            </Button>
+            <Button
+              onClick={() => {
+                if (!resolveTarget) return
+                resolveMutation.mutate({
+                  id: resolveTarget.id,
+                  status: resolveTarget.status,
+                  resolutionNote: resolutionNote.trim() || undefined,
+                })
+              }}
+              disabled={resolveMutation.isPending}
+            >
+              {resolveMutation.isPending ? (
+                <Loader2 className="h-4 w-4 animate-spin" />
+              ) : resolveTarget?.status === 'RESOLVED' ? (
+                'Mark Resolved'
+              ) : (
+                'Dismiss'
+              )}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+    </>
+  )
+}
+
+type ChangeRequestRowProps = {
+  request: {
+    id: string
+    reason: string
+    createdAt: Date
+    requestedBy: { id: string; name: string | null; email: string } | null
+    targetAssignment: {
+      id: string
+      mentor: { id: string; name: string | null; email: string }
+    } | null
+  }
+  onResolve: (status: 'RESOLVED' | 'DISMISSED') => void
+}
+
+function ChangeRequestRow({ request, onResolve }: ChangeRequestRowProps) {
+  const [expanded, setExpanded] = useState(false)
+  const reasonIsLong = request.reason.length > 240
+  return (
+    <li className="rounded-md border bg-card p-4">
+      <div className="flex items-start justify-between gap-4">
+        <div className="min-w-0 flex-1 space-y-2">
+          <div className="flex flex-wrap items-center gap-x-3 gap-y-1 text-sm">
+            <span className="font-medium">
+              {request.requestedBy?.name ?? request.requestedBy?.email ?? 'Unknown'}
+            </span>
+            {request.requestedBy?.email && request.requestedBy.name && (
+              <span className="text-muted-foreground text-xs">
+                {request.requestedBy.email}
+              </span>
+            )}
+            <span className="text-muted-foreground text-xs">
+              ·{' '}
+              {new Date(request.createdAt).toLocaleDateString(undefined, {
+                year: 'numeric',
+                month: 'short',
+                day: 'numeric',
+              })}
+            </span>
+          </div>
+          {request.targetAssignment && (
+            <div className="text-muted-foreground text-xs">
+              About:{' '}
+              <span className="font-medium">
+                {request.targetAssignment.mentor.name ||
+                  request.targetAssignment.mentor.email}
+              </span>
+            </div>
+          )}
+          <p
+            className={
+              expanded || !reasonIsLong
+                ? 'text-sm whitespace-pre-wrap'
+                : 'text-sm whitespace-pre-wrap line-clamp-4'
+            }
+          >
+            {request.reason}
+          </p>
+          {reasonIsLong && (
+            <button
+              type="button"
+              className="text-primary text-xs hover:underline"
+              onClick={() => setExpanded((v) => !v)}
+            >
+              {expanded ? 'Show less' : 'Show more'}
+            </button>
           )}
         </div>
+        <div className="flex shrink-0 flex-col gap-2">
+          <Button size="sm" onClick={() => onResolve('RESOLVED')}>
+            Mark Resolved
+          </Button>
+          <Button
+            size="sm"
+            variant="outline"
+            onClick={() => onResolve('DISMISSED')}
+          >
+            Dismiss
+          </Button>
+        </div>
+      </div>
+    </li>
   )
 }
 

src/components/admin/round/mentoring-round-overview.tsx

@@ -9,6 +9,7 @@ import {
   ArrowRight,
   Clock,
   FileText,
+  Inbox,
   MessageCircle,
   Target,
   UserCheck,
@@ -48,6 +49,10 @@ export function MentoringRoundOverview({ roundId }: Props) {
     { refetchInterval: 30_000 },
   )
   const { data: pool, isLoading: poolLoading } = trpc.mentor.getMentorPool.useQuery({})
+  const { data: pendingChangeRequests } = trpc.mentor.listChangeRequests.useQuery(
+    { status: 'PENDING' },
+    { refetchInterval: 30_000 },
+  )
 
   if (statsLoading || poolLoading) {
     return (
@@ -60,6 +65,15 @@ export function MentoringRoundOverview({ roundId }: Props) {
   }
   if (!stats || !pool) return null
 
+  const pendingCount = pendingChangeRequests?.length ?? 0
+  // If there's at least one pending request, deep-link directly into the
+  // first one's project (admins can resolve / view siblings from there).
+  // Otherwise the card stays static.
+  const firstPendingProjectId = pendingChangeRequests?.[0]?.project.id ?? null
+  const changeRequestsHref = firstPendingProjectId
+    ? `/admin/projects/${firstPendingProjectId}/mentor`
+    : null
+
   const requestedPct = stats.totalProjects
     ? Math.round((stats.requestedCount / stats.totalProjects) * 100)
     : 0
@@ -173,6 +187,42 @@ export function MentoringRoundOverview({ roundId }: Props) {
         </CardContent>
       </Card>
 
+      <Card
+        className={`md:col-span-2 xl:col-span-4 ${
+          pendingCount > 0 ? 'border-amber-300 dark:border-amber-700' : ''
+        }`}
+      >
+        <CardContent className="flex items-center justify-between py-4">
+          <div className="flex items-center gap-3">
+            <Inbox
+              className={`h-5 w-5 ${
+                pendingCount > 0 ? 'text-amber-600' : 'text-muted-foreground'
+              }`}
+            />
+            <div>
+              <div className="text-sm font-medium">Pending change requests</div>
+              <div className="text-muted-foreground text-xs">
+                Team members asking admin to swap a mentor
+              </div>
+            </div>
+          </div>
+          <div className="flex items-center gap-3">
+            <div className="text-2xl font-bold tabular-nums">{pendingCount}</div>
+            {changeRequestsHref ? (
+              <Link
+                href={changeRequestsHref}
+                className="text-muted-foreground hover:text-foreground inline-flex items-center text-xs"
+              >
+                Review
+                <ArrowRight className="ml-0.5 h-3 w-3" />
+              </Link>
+            ) : (
+              <span className="text-muted-foreground text-xs">All clear</span>
+            )}
+          </div>
+        </CardContent>
+      </Card>
+
       <Card className="md:col-span-2 xl:col-span-4">
         <CardHeader className="pb-2">
           <CardTitle className="text-sm">Workspace activity</CardTitle>

src/server/routers/mentor.ts

@@ -565,16 +565,34 @@ export const mentorRouter = router({
     }),
 
   /**
-   * Remove mentor assignment
+   * Remove mentor assignment.
+   *
+   * Multi-mentor (PR8): callers should pass `assignmentId` to target a
+   * specific co-mentor. Legacy callers passing only `projectId` get the
+   * most-recent assignment removed (kept for backward compatibility).
    */
   unassign: adminProcedure
-    .input(z.object({ projectId: z.string() }))
+    .input(
+      z
+        .object({
+          assignmentId: z.string().optional(),
+          projectId: z.string().optional(),
+        })
+        .refine((v) => !!v.assignmentId || !!v.projectId, {
+          message: 'Either assignmentId or projectId is required',
+        }),
+    )
     .mutation(async ({ ctx, input }) => {
-      // TODO(PR8 Task 8): admin UI should specify which mentor to drop when
+      const assignment = input.assignmentId
-      // multiple are assigned. Legacy callers pass only projectId — we resolve
+        ? await ctx.prisma.mentorAssignment.findUnique({
-      // to the most-recent assignment for backward compatibility.
+            where: { id: input.assignmentId },
-      const assignment = await ctx.prisma.mentorAssignment.findFirst({
+            include: {
-        where: { projectId: input.projectId },
+              mentor: { select: { id: true, name: true } },
+              project: { select: { id: true, title: true } },
+            },
+          })
+        : await ctx.prisma.mentorAssignment.findFirst({
+            where: { projectId: input.projectId! },
             orderBy: { assignedAt: 'desc' },
             include: {
               mentor: { select: { id: true, name: true } },
@@ -585,7 +603,7 @@ export const mentorRouter = router({
       if (!assignment) {
         throw new TRPCError({
           code: 'NOT_FOUND',
-          message: 'No mentor assignment found for this project',
+          message: 'No mentor assignment found',
         })
       }
 
@@ -602,7 +620,7 @@ export const mentorRouter = router({
         entityType: 'MentorAssignment',
         entityId: assignment.id,
         detailsJson: {
-          projectId: input.projectId,
+          projectId: assignment.project.id,
           projectTitle: assignment.project.title,
           mentorId: assignment.mentor.id,
           mentorName: assignment.mentor.name,