feat(mentor): many-to-many bulk assignment (multi-mentor × multi-project)

mentor.bulkAssign now accepts mentorIds[] instead of a single mentorId and
creates the cartesian product of (mentor, project) assignments. Existing
active (mentor, project) pairs are skipped per-pair, not per-project, so
choosing two mentors against a project that already has one of them still
adds the second.

Email coalescing stays one-per-mentor: each mentor receives a single email
listing only their own newly-assigned projects (not the union). Each touched
project still triggers a single team-introduction email when its MENTORING
round is ROUND_ACTIVE, listing all currently-active mentors on that team.

Dialog UI swaps the radio picker for a checkbox group with a removable chip
strip for selected mentors, a live preview of the assignment count
(mentors × projects = up to N), and a submit button that names both
counts. Toast on success reports total assignments created, projects
touched, pairs skipped, and how many mentor emails went out.

src/components/admin/round/mentoring-projects-table.tsx

@@ -43,7 +43,7 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
   const [filter, setFilter] = useState<Filter>('all')
   const [selected, setSelected] = useState<Set<string>>(new Set())
   const [bulkOpen, setBulkOpen] = useState(false)
-  const [chosenMentorId, setChosenMentorId] = useState<string>('')
+  const [chosenMentorIds, setChosenMentorIds] = useState<Set<string>>(new Set())
   const [mentorSearch, setMentorSearch] = useState('')
 
   const utils = trpc.useUtils()
@@ -63,17 +63,28 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
 
   const bulkAssignMutation = trpc.mentor.bulkAssign.useMutation({
     onSuccess: (result) => {
-      if (result.assignedCount === 0 && result.skippedCount > 0) {
+      if (result.totalAssigned === 0 && result.totalSkipped > 0) {
         toast.info(
-          `No new assignments — the selected mentor is already on all ${result.skippedCount} project${result.skippedCount === 1 ? '' : 's'}.`,
+          `No new assignments — every selected mentor is already on every selected project (${result.totalSkipped} pair${result.totalSkipped === 1 ? '' : 's'} skipped).`,
         )
       } else {
+        const mentorCount = result.perMentor.filter((m) => m.assigned > 0).length
         toast.success(
-          `Assigned mentor to ${result.assignedCount} project${
-            result.assignedCount === 1 ? '' : 's'
-          }${result.skippedCount > 0 ? ` (${result.skippedCount} already had this mentor)` : ''}${
-            result.emailSent ? ' · email sent' : ''
+          `Created ${result.totalAssigned} assignment${
+            result.totalAssigned === 1 ? '' : 's'
+          } across ${result.touchedProjectCount} project${
+            result.touchedProjectCount === 1 ? '' : 's'
+          }${result.totalSkipped > 0 ? ` (${result.totalSkipped} pair${result.totalSkipped === 1 ? '' : 's'} already existed)` : ''}${
+            result.emailsSent > 0
+              ? ` · ${result.emailsSent} mentor email${result.emailsSent === 1 ? '' : 's'} sent`
+              : ''
           }`,
+          {
+            description:
+              mentorCount > 1
+                ? `Each of ${mentorCount} mentors gets a single combined email listing only their new projects.`
+                : undefined,
+          },
         )
       }
       utils.round.listMentoringProjects.invalidate({ roundId })
@@ -83,7 +94,7 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
       utils.mentor.getRoundStats.invalidate({ roundId })
       utils.project.list.invalidate()
       setSelected(new Set())
-      setChosenMentorId('')
+      setChosenMentorIds(new Set())
       setMentorSearch('')
       setBulkOpen(false)
     },
@@ -442,7 +453,7 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
         onOpenChange={(next) => {
           if (!next) {
             setBulkOpen(false)
-            setChosenMentorId('')
+            setChosenMentorIds(new Set())
             setMentorSearch('')
           }
         }}
@@ -450,17 +461,55 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
         <DialogContent>
           <DialogHeader>
             <DialogTitle>
-              Assign mentor to {selected.size} project
+              Assign mentors to {selected.size} project
               {selected.size === 1 ? '' : 's'}
             </DialogTitle>
             <DialogDescription>
-              Choose one mentor — they'll receive a single email listing every
-              new assignment. Projects where they're already an active mentor
-              will be skipped.
+              Tick any number of mentors. Each chosen mentor will be added to
+              every selected project they aren&apos;t already on. Each mentor
+              receives one combined email; each team receives one intro email
+              listing all of their mentors.
             </DialogDescription>
           </DialogHeader>
 
           <div className="space-y-3">
+            {(() => {
+              const allMentors = mentorPool?.mentors ?? []
+              const chosenMentors = allMentors.filter((m) =>
+                chosenMentorIds.has(m.id),
+              )
+              const upperBound = chosenMentorIds.size * selected.size
+
+              return (
+                <>
+                  {chosenMentors.length > 0 && (
+                    <div className="flex flex-wrap gap-1 rounded-md border bg-muted/30 p-2">
+                      {chosenMentors.map((m) => (
+                        <Badge
+                          key={m.id}
+                          variant="secondary"
+                          className="gap-1 pl-2 pr-1"
+                        >
+                          {m.name ?? m.email}
+                          <button
+                            type="button"
+                            aria-label={`Remove ${m.name ?? m.email}`}
+                            className="rounded-full p-0.5 hover:bg-foreground/10"
+                            onClick={() =>
+                              setChosenMentorIds((prev) => {
+                                const next = new Set(prev)
+                                next.delete(m.id)
+                                return next
+                              })
+                            }
+                          >
+                            <X className="h-3 w-3" />
+                          </button>
+                        </Badge>
+                      ))}
+                    </div>
+                  )}
+
                   <div className="relative">
                     <Search className="absolute left-2.5 top-1/2 h-3.5 w-3.5 -translate-y-1/2 text-muted-foreground" />
                     <Input
@@ -470,12 +519,12 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                       className="pl-8"
                     />
                   </div>
+
                   <div className="max-h-72 overflow-y-auto rounded-md border">
                     {(() => {
-                const mentors = mentorPool?.mentors ?? []
                       const q = mentorSearch.trim().toLowerCase()
                       const filteredMentors = q
-                  ? mentors.filter((m) =>
+                        ? allMentors.filter((m) =>
                             [
                               m.name ?? '',
                               m.email,
@@ -486,8 +535,8 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                               .toLowerCase()
                               .includes(q),
                           )
-                  : mentors
-                if (mentors.length === 0) {
+                        : allMentors
+                      if (allMentors.length === 0) {
                         return (
                           <p className="p-4 text-center text-sm text-muted-foreground">
                             No mentors in the pool yet.{' '}
@@ -509,7 +558,7 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                         )
                       }
                       return filteredMentors.map((m) => {
-                  const isChosen = chosenMentorId === m.id
+                        const isChosen = chosenMentorIds.has(m.id)
                         return (
                           <label
                             key={m.id}
@@ -517,12 +566,18 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                               isChosen ? 'bg-accent' : 'hover:bg-muted/50'
                             }`}
                           >
-                      <input
-                        type="radio"
-                        name="bulk-mentor"
+                            <Checkbox
                               className="mt-1"
                               checked={isChosen}
-                        onChange={() => setChosenMentorId(m.id)}
+                              onCheckedChange={(checked) =>
+                                setChosenMentorIds((prev) => {
+                                  const next = new Set(prev)
+                                  if (checked) next.add(m.id)
+                                  else next.delete(m.id)
+                                  return next
+                                })
+                              }
+                              aria-label={`Toggle ${m.name ?? m.email}`}
                             />
                             <div className="min-w-0 flex-1">
                               <div className="font-medium">
@@ -544,7 +599,10 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                                     </Badge>
                                   ))}
                                   {m.expertiseTags.length > 4 && (
-                              <Badge variant="outline" className="text-[10px]">
+                                    <Badge
+                                      variant="outline"
+                                      className="text-[10px]"
+                                    >
                                       +{m.expertiseTags.length - 4}
                                     </Badge>
                                   )}
@@ -561,6 +619,23 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
                       })
                     })()}
                   </div>
+
+                  {chosenMentorIds.size > 0 && (
+                    <p className="text-xs text-muted-foreground">
+                      Will create up to{' '}
+                      <span className="font-medium tabular-nums text-foreground">
+                        {upperBound}
+                      </span>{' '}
+                      assignment{upperBound === 1 ? '' : 's'} (
+                      {chosenMentorIds.size} mentor
+                      {chosenMentorIds.size === 1 ? '' : 's'} × {selected.size}{' '}
+                      project{selected.size === 1 ? '' : 's'}). Pairs that
+                      already exist are skipped.
+                    </p>
+                  )}
+                </>
+              )
+            })()}
           </div>
 
           <DialogFooter>
@@ -568,7 +643,7 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
               variant="outline"
               onClick={() => {
                 setBulkOpen(false)
-                setChosenMentorId('')
+                setChosenMentorIds(new Set())
                 setMentorSearch('')
               }}
             >
@@ -577,16 +652,19 @@ export function MentoringProjectsTable({ roundId }: { roundId: string }) {
             <Button
               onClick={() =>
                 bulkAssignMutation.mutate({
-                  mentorId: chosenMentorId,
+                  mentorIds: Array.from(chosenMentorIds),
                   projectIds: Array.from(selected),
                 })
               }
-              disabled={!chosenMentorId || bulkAssignMutation.isPending}
+              disabled={
+                chosenMentorIds.size === 0 || bulkAssignMutation.isPending
+              }
             >
               {bulkAssignMutation.isPending && (
                 <Loader2 className="mr-1.5 h-4 w-4 animate-spin" />
               )}
-              Assign to {selected.size} project
+              Assign {chosenMentorIds.size} mentor
+              {chosenMentorIds.size === 1 ? '' : 's'} to {selected.size} project
               {selected.size === 1 ? '' : 's'}
             </Button>
           </DialogFooter>

src/server/routers/mentor.ts

@@ -648,33 +648,30 @@ export const mentorRouter = router({
     }),
 
   /**
-   * Bulk-assign ONE mentor to MANY projects in a single transaction. Skips
-   * projects where this mentor is already an active mentor. Sends a single
-   * coalesced email to the mentor listing all newly-assigned projects.
-   * In-app notifications are still per-project so each team is notified.
+   * Bulk-assign MANY mentors to MANY projects (cartesian product) in one
+   * call. Skips (mentor, project) pairs where the mentor is already an
+   * active mentor on that project. Each affected mentor receives ONE
+   * coalesced email listing only their newly-assigned projects. Each team
+   * whose project's MENTORING round is already open receives ONE intro
+   * email listing all their active mentors (including any pre-existing).
    */
   bulkAssign: adminProcedure
     .input(
       z.object({
-        mentorId: z.string(),
+        mentorIds: z.array(z.string()).min(1),
         projectIds: z.array(z.string()).min(1),
       }),
     )
     .mutation(async ({ ctx, input }) => {
-      const mentor = await ctx.prisma.user.findUnique({
-        where: { id: input.mentorId },
-        select: {
-          id: true,
-          name: true,
-          email: true,
-          roles: true,
-          status: true,
-        },
+      const mentors = await ctx.prisma.user.findMany({
+        where: { id: { in: input.mentorIds } },
+        select: { id: true, name: true, email: true, roles: true },
       })
-      if (!mentor || !mentor.roles.includes('MENTOR')) {
+      const validMentors = mentors.filter((m) => m.roles.includes('MENTOR'))
+      if (validMentors.length === 0) {
         throw new TRPCError({
           code: 'BAD_REQUEST',
-          message: 'Selected user is not a mentor',
+          message: 'None of the selected users have the MENTOR role',
         })
       }
 
@@ -684,58 +681,89 @@ export const mentorRouter = router({
           id: true,
           title: true,
           mentorAssignments: {
-            where: { mentorId: mentor.id, droppedAt: null },
-            select: { id: true },
+            where: {
+              mentorId: { in: validMentors.map((m) => m.id) },
+              droppedAt: null,
+            },
+            select: { mentorId: true },
           },
         },
       })
 
-      const newProjects: { id: string; title: string }[] = []
-      const skippedProjects: { id: string; title: string }[] = []
-      const createdAssignmentIds: string[] = []
+      // Track per-mentor (for emails) and per-project (for team intros) state.
+      const perMentor = new Map<
+        string,
+        {
+          email: string | null
+          name: string | null
+          assignmentIds: string[]
+          newProjects: { id: string; title: string }[]
+          skippedProjects: { id: string; title: string }[]
+        }
+      >()
+      for (const m of validMentors) {
+        perMentor.set(m.id, {
+          email: m.email ?? null,
+          name: m.name ?? null,
+          assignmentIds: [],
+          newProjects: [],
+          skippedProjects: [],
+        })
+      }
+      const touchedProjectIds = new Set<string>()
+      let totalAssigned = 0
+      let totalSkipped = 0
 
-      for (const p of projects) {
-        if (p.mentorAssignments.length > 0) {
-          skippedProjects.push({ id: p.id, title: p.title })
+      for (const project of projects) {
+        const alreadyOn = new Set(project.mentorAssignments.map((a) => a.mentorId))
+        for (const mentor of validMentors) {
+          const bucket = perMentor.get(mentor.id)!
+          if (alreadyOn.has(mentor.id)) {
+            bucket.skippedProjects.push({ id: project.id, title: project.title })
+            totalSkipped++
             continue
           }
           const created = await ctx.prisma.mentorAssignment.create({
             data: {
-            projectId: p.id,
+              projectId: project.id,
               mentorId: mentor.id,
               method: 'MANUAL',
               assignedBy: ctx.user.id,
             },
           })
-        createdAssignmentIds.push(created.id)
-        newProjects.push({ id: p.id, title: p.title })
+          bucket.assignmentIds.push(created.id)
+          bucket.newProjects.push({ id: project.id, title: project.title })
+          touchedProjectIds.add(project.id)
+          totalAssigned++
 
           await createNotification({
             userId: mentor.id,
             type: NotificationTypes.MENTEE_ASSIGNED,
             title: 'New Mentee Assigned',
-          message: `You have been assigned to mentor "${p.title}".`,
-          linkUrl: `/mentor/projects/${p.id}`,
+            message: `You have been assigned to mentor "${project.title}".`,
+            linkUrl: `/mentor/projects/${project.id}`,
             linkLabel: 'View Project',
             priority: 'high',
-          metadata: { projectName: p.title },
+            metadata: { projectName: project.title },
           })
 
-        await notifyProjectTeam(p.id, {
+          await notifyProjectTeam(project.id, {
             type: NotificationTypes.MENTOR_ASSIGNED,
             title: 'Mentor Assigned',
             message: `${mentor.name || 'A mentor'} has been assigned to support your project.`,
-          linkUrl: `/team/projects/${p.id}`,
+            linkUrl: `/team/projects/${project.id}`,
             linkLabel: 'View Project',
             priority: 'high',
-          metadata: { projectName: p.title, mentorName: mentor.name },
+            metadata: { projectName: project.title, mentorName: mentor.name },
           })
+        }
 
-        // Trigger MENTORING round IN_PROGRESS state transition (best-effort)
+        // Best-effort: mark project IN_PROGRESS in the active MENTORING round
+        if (touchedProjectIds.has(project.id)) {
           try {
             const mentoringPrs = await ctx.prisma.projectRoundState.findFirst({
               where: {
-              projectId: p.id,
+                projectId: project.id,
                 round: {
                   roundType: 'MENTORING',
                   status: { in: ['ROUND_ACTIVE', 'ROUND_CLOSED'] },
@@ -746,7 +774,7 @@ export const mentorRouter = router({
             })
             if (mentoringPrs) {
               await triggerInProgressOnActivity(
-              p.id,
+                project.id,
                 mentoringPrs.roundId,
                 ctx.user.id,
                 ctx.prisma,
@@ -759,45 +787,63 @@ export const mentorRouter = router({
             )
           }
         }
+      }
 
-      // One coalesced email per mentor, with all NEW project assignments.
-      if (newProjects.length > 0 && mentor.email) {
-        await sendMentorBulkAssignmentEmail(mentor.email, mentor.name, newProjects)
-        // Stamp notificationSentAt on every row we just created so single-
-        // assignment retries don't re-notify.
+      // One email per mentor, listing only their NEW projects.
+      for (const bucket of perMentor.values()) {
+        if (bucket.newProjects.length === 0 || !bucket.email) continue
+        await sendMentorBulkAssignmentEmail(
+          bucket.email,
+          bucket.name,
+          bucket.newProjects,
+        )
         await ctx.prisma.mentorAssignment.updateMany({
-          where: { id: { in: createdAssignmentIds } },
+          where: { id: { in: bucket.assignmentIds } },
           data: { notificationSentAt: new Date() },
         })
       }
 
-      // For each newly-assigned project whose MENTORING round is already open,
-      // introduce the team to the mentor(s) by email.
-      for (const p of newProjects) {
-        await introduceTeamToMentorsIfRoundOpen(ctx.prisma, p.id)
+      // One team-intro email per touched project (only if MENTORING round
+      // is currently ROUND_ACTIVE). The helper lists ALL active mentors on
+      // the project, including any pre-existing co-mentors.
+      for (const projectId of touchedProjectIds) {
+        await introduceTeamToMentorsIfRoundOpen(ctx.prisma, projectId)
       }
 
       await logAudit({
         prisma: ctx.prisma,
         userId: ctx.user.id,
         action: 'MENTOR_BULK_ASSIGN',
-        entityType: 'User',
-        entityId: mentor.id,
+        entityType: 'BulkAssign',
+        entityId: 'multi',
         detailsJson: {
-          mentorEmail: mentor.email,
-          assignedCount: newProjects.length,
-          skippedCount: skippedProjects.length,
-          newProjectIds: newProjects.map((p) => p.id),
+          mentorIds: validMentors.map((m) => m.id),
+          projectIds: input.projectIds,
+          totalAssigned,
+          totalSkipped,
+          perMentor: Array.from(perMentor.entries()).map(([id, b]) => ({
+            mentorId: id,
+            assigned: b.newProjects.length,
+            skipped: b.skippedProjects.length,
+          })),
         },
         ipAddress: ctx.ip,
         userAgent: ctx.userAgent,
       })
 
       return {
-        assignedCount: newProjects.length,
-        skippedCount: skippedProjects.length,
-        skippedProjects,
-        emailSent: newProjects.length > 0,
+        totalAssigned,
+        totalSkipped,
+        touchedProjectCount: touchedProjectIds.size,
+        perMentor: Array.from(perMentor.entries()).map(([id, b]) => ({
+          mentorId: id,
+          mentorName: b.name,
+          assigned: b.newProjects.length,
+          skipped: b.skippedProjects.length,
+        })),
+        emailsSent: Array.from(perMentor.values()).filter(
+          (b) => b.newProjects.length > 0 && b.email,
+        ).length,
       }
     }),