feat: mentor self-drop with required reason

Adds mentor.dropAssignment mutation (mentor-only, ownership-checked, reason
min 10 chars). Filters dropped MentorAssignment rows out of getMyProjects,
getCandidates mentor count, getMentorPool, and getMenteeActivity so they
no longer surface in the mentor or admin UI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/server/routers/mentor.ts

@@ -178,7 +178,7 @@ export const mentorRouter = router({
           country: true,
           expertiseTags: true,
           maxAssignments: true,
-          mentorAssignments: { select: { id: true } },
+          mentorAssignments: { where: { droppedAt: null }, select: { id: true } },
         },
       })
 
@@ -1006,7 +1006,10 @@ export const mentorRouter = router({
           expertiseTags: true,
           maxAssignments: true,
           mentorAssignments: {
-            where: input.programId ? { project: { programId: input.programId } } : undefined,
+            where: {
+              droppedAt: null,
+              ...(input.programId ? { project: { programId: input.programId } } : {}),
+            },
             select: {
               completionStatus: true,
               messages: {
@@ -1099,13 +1102,18 @@ export const mentorRouter = router({
               method: true,
               assignedAt: true,
               completionStatus: true,
+              droppedAt: true,
               mentor: {
                 select: {
                   id: true,
                   name: true,
                   email: true,
                   maxAssignments: true,
-                  _count: { select: { mentorAssignments: true } },
+                  _count: {
+                    select: {
+                      mentorAssignments: { where: { droppedAt: null } },
+                    },
+                  },
                 },
               },
               messages: {
@@ -1137,7 +1145,8 @@ export const mentorRouter = router({
       const totals = { unassigned: 0, assigned: 0, active: 0, stalled: 0 }
 
       const rows = projects.map((p) => {
-        const ma = p.mentorAssignment
+        // Treat a dropped mentor assignment as if no mentor is assigned.
+        const ma = p.mentorAssignment && !p.mentorAssignment.droppedAt ? p.mentorAssignment : null
         const lastMessageAt = ma?.messages[0]?.createdAt ?? null
         const lastFileAt = ma?.files[0]?.createdAt ?? null
         const lastActivityAt = [lastMessageAt, lastFileAt]
@@ -1196,7 +1205,7 @@ export const mentorRouter = router({
    */
   getMyProjects: mentorProcedure.query(async ({ ctx }) => {
     const assignments = await ctx.prisma.mentorAssignment.findMany({
-      where: { mentorId: ctx.user.id },
+      where: { mentorId: ctx.user.id, droppedAt: null },
       include: {
         project: {
           include: {
@@ -2205,4 +2214,91 @@ export const mentorRouter = router({
       }
       return result
     }),
+
+  /**
+   * Mentor self-drops an assignment with a required reason. Notifies all
+   * program admins so they can re-assign. Audit-logged.
+   */
+  dropAssignment: mentorProcedure
+    .input(
+      z.object({
+        assignmentId: z.string(),
+        reason: z
+          .string()
+          .min(10, 'Reason must be at least 10 characters')
+          .max(500),
+      }),
+    )
+    .mutation(async ({ ctx, input }) => {
+      const assignment = await ctx.prisma.mentorAssignment.findUniqueOrThrow({
+        where: { id: input.assignmentId },
+        include: {
+          project: { select: { id: true, title: true } },
+        },
+      })
+      if (assignment.mentorId !== ctx.user.id) {
+        throw new TRPCError({
+          code: 'FORBIDDEN',
+          message: 'This is not your assignment',
+        })
+      }
+      if (assignment.droppedAt) {
+        throw new TRPCError({
+          code: 'BAD_REQUEST',
+          message: 'Assignment is already dropped',
+        })
+      }
+      if (assignment.completionStatus === 'completed') {
+        throw new TRPCError({
+          code: 'BAD_REQUEST',
+          message: 'Assignment is already completed',
+        })
+      }
+
+      const dropped = await ctx.prisma.mentorAssignment.update({
+        where: { id: assignment.id },
+        data: {
+          droppedAt: new Date(),
+          droppedReason: input.reason,
+          droppedBy: 'mentor',
+        },
+      })
+
+      // Notify program admins (best-effort, never block the drop)
+      try {
+        const admins = await ctx.prisma.user.findMany({
+          where: {
+            roles: { hasSome: ['SUPER_ADMIN', 'PROGRAM_ADMIN'] },
+            status: { not: 'SUSPENDED' },
+          },
+          select: { id: true },
+        })
+        const mentorName = ctx.user.name ?? ctx.user.email
+        for (const admin of admins) {
+          await createNotification({
+            userId: admin.id,
+            type: NotificationTypes.MENTOR_DROPPED,
+            title: 'Mentor dropped a team',
+            message: `${mentorName} dropped their mentee "${assignment.project.title}". Reason: ${input.reason}`,
+            linkUrl: `/admin/projects/${assignment.project.id}/mentor`,
+            priority: 'high',
+          })
+        }
+      } catch (err) {
+        console.error('[mentor.dropAssignment] notify admins failed:', err)
+      }
+
+      await logAudit({
+        prisma: ctx.prisma,
+        userId: ctx.user.id,
+        action: 'MENTOR_DROP_ASSIGNMENT',
+        entityType: 'MentorAssignment',
+        entityId: assignment.id,
+        detailsJson: {
+          reason: input.reason,
+          projectId: assignment.project.id,
+        },
+      })
+      return dropped
+    }),
 })