feat(schema): multi-mentor per team + change-requests + per-assignment email field

- MentorAssignment: drop projectId @unique -> composite (projectId, mentorId)
- MentorAssignment: add notificationSentAt for idempotent per-team email
- MentorFile: add projectId (primary scope); mentorAssignmentId becomes nullable audit FK
- MentorChangeRequest: new model + status enum
- Migration hand-written with IF EXISTS guards (safe for docker-entrypoint retry)

prisma/migrations/20260522155652_multi_mentor_per_team/migration.sql

@@ -0,0 +1,78 @@
+-- Hand-written migration for PR8 (multi-mentor per team).
+--
+-- All DDL guarded with IF EXISTS / IF NOT EXISTS so the docker-entrypoint
+-- retry loop is safe to re-run. No regex (the 2026-05-07 prod incident was
+-- caused by Prisma 6 generating regex-based DDL that Postgres rejected).
+-- No BEGIN/COMMIT blocks — Prisma wraps the migration in a transaction.
+
+-- Phase 1: MentorAssignment — drop unique, add composite, add notification field
+ALTER TABLE "MentorAssignment" DROP CONSTRAINT IF EXISTS "MentorAssignment_projectId_key";
+DROP INDEX IF EXISTS "MentorAssignment_projectId_key";
+CREATE UNIQUE INDEX IF NOT EXISTS "MentorAssignment_projectId_mentorId_key"
+  ON "MentorAssignment"("projectId", "mentorId");
+CREATE INDEX IF NOT EXISTS "MentorAssignment_projectId_idx"
+  ON "MentorAssignment"("projectId");
+ALTER TABLE "MentorAssignment" ADD COLUMN IF NOT EXISTS "notificationSentAt" TIMESTAMP(3);
+
+-- Phase 2: MentorFile — re-scope to project (two-phase backfill)
+ALTER TABLE "MentorFile" ADD COLUMN IF NOT EXISTS "projectId" TEXT;
+UPDATE "MentorFile" mf
+   SET "projectId" = ma."projectId"
+  FROM "MentorAssignment" ma
+ WHERE mf."mentorAssignmentId" = ma."id"
+   AND mf."projectId" IS NULL;
+ALTER TABLE "MentorFile" ALTER COLUMN "projectId" SET NOT NULL;
+ALTER TABLE "MentorFile" DROP CONSTRAINT IF EXISTS "MentorFile_projectId_fkey";
+ALTER TABLE "MentorFile" ADD CONSTRAINT "MentorFile_projectId_fkey"
+  FOREIGN KEY ("projectId") REFERENCES "Project"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+CREATE INDEX IF NOT EXISTS "MentorFile_projectId_idx" ON "MentorFile"("projectId");
+
+-- Phase 2b: Make MentorFile.mentorAssignmentId nullable + switch its FK to SetNull
+ALTER TABLE "MentorFile" ALTER COLUMN "mentorAssignmentId" DROP NOT NULL;
+ALTER TABLE "MentorFile" DROP CONSTRAINT IF EXISTS "MentorFile_mentorAssignmentId_fkey";
+ALTER TABLE "MentorFile" ADD CONSTRAINT "MentorFile_mentorAssignmentId_fkey"
+  FOREIGN KEY ("mentorAssignmentId") REFERENCES "MentorAssignment"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+-- Phase 3: MentorChangeRequest table
+-- Postgres < 14 doesn't support CREATE TYPE ... IF NOT EXISTS, so wrap in a
+-- DO block that swallows duplicate_object errors (idempotent for re-runs).
+DO $$ BEGIN
+  CREATE TYPE "MentorChangeRequestStatus" AS ENUM ('PENDING', 'RESOLVED', 'DISMISSED');
+EXCEPTION
+  WHEN duplicate_object THEN NULL;
+END $$;
+
+CREATE TABLE IF NOT EXISTS "MentorChangeRequest" (
+  "id"                  TEXT NOT NULL,
+  "projectId"           TEXT NOT NULL,
+  "targetAssignmentId"  TEXT,
+  "requestedByUserId"   TEXT,
+  "reason"              TEXT NOT NULL,
+  "status"              "MentorChangeRequestStatus" NOT NULL DEFAULT 'PENDING',
+  "resolvedByUserId"    TEXT,
+  "resolvedAt"          TIMESTAMP(3),
+  "resolutionNote"      TEXT,
+  "createdAt"           TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  "updatedAt"           TIMESTAMP(3) NOT NULL,
+  CONSTRAINT "MentorChangeRequest_pkey" PRIMARY KEY ("id")
+);
+
+ALTER TABLE "MentorChangeRequest" DROP CONSTRAINT IF EXISTS "MentorChangeRequest_projectId_fkey";
+ALTER TABLE "MentorChangeRequest" ADD CONSTRAINT "MentorChangeRequest_projectId_fkey"
+  FOREIGN KEY ("projectId") REFERENCES "Project"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+ALTER TABLE "MentorChangeRequest" DROP CONSTRAINT IF EXISTS "MentorChangeRequest_targetAssignmentId_fkey";
+ALTER TABLE "MentorChangeRequest" ADD CONSTRAINT "MentorChangeRequest_targetAssignmentId_fkey"
+  FOREIGN KEY ("targetAssignmentId") REFERENCES "MentorAssignment"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+ALTER TABLE "MentorChangeRequest" DROP CONSTRAINT IF EXISTS "MentorChangeRequest_requestedByUserId_fkey";
+ALTER TABLE "MentorChangeRequest" ADD CONSTRAINT "MentorChangeRequest_requestedByUserId_fkey"
+  FOREIGN KEY ("requestedByUserId") REFERENCES "User"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+ALTER TABLE "MentorChangeRequest" DROP CONSTRAINT IF EXISTS "MentorChangeRequest_resolvedByUserId_fkey";
+ALTER TABLE "MentorChangeRequest" ADD CONSTRAINT "MentorChangeRequest_resolvedByUserId_fkey"
+  FOREIGN KEY ("resolvedByUserId") REFERENCES "User"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+CREATE INDEX IF NOT EXISTS "MentorChangeRequest_projectId_idx" ON "MentorChangeRequest"("projectId");
+CREATE INDEX IF NOT EXISTS "MentorChangeRequest_status_idx" ON "MentorChangeRequest"("status");
+CREATE INDEX IF NOT EXISTS "MentorChangeRequest_targetAssignmentId_idx" ON "MentorChangeRequest"("targetAssignmentId");

prisma/schema.prisma

@@ -118,7 +118,6 @@ enum NotificationChannel {
   NONE
 }
 
-
 enum PartnerVisibility {
   ADMIN_ONLY
   JURY_VISIBLE
@@ -133,7 +132,6 @@ enum PartnerType {
   OTHER
 }
 
-
 // =============================================================================
 // COMPETITION / ROUND ENGINE ENUMS
 // =============================================================================
@@ -171,7 +169,6 @@ enum ProjectRoundStateValue {
   WITHDRAWN
 }
 
-
 enum CapMode {
   HARD
   SOFT
@@ -428,6 +425,10 @@ model User {
   // Grand-finale logistics
   finalistAttendances AttendingMember[]
 
+  // Mentor change requests
+  mentorChangeRequestsRequested MentorChangeRequest[] @relation("MentorChangeRequester")
+  mentorChangeRequestsResolved  MentorChangeRequest[] @relation("MentorChangeResolver")
+
   @@index([role])
   @@index([status])
 }
@@ -629,7 +630,9 @@ model Project {
   assignments           Assignment[]
   submittedBy           User?                  @relation("ProjectSubmittedBy", fields: [submittedByUserId], references: [id], onDelete: SetNull)
   teamMembers           TeamMember[]
-  mentorAssignment      MentorAssignment?
+  mentorAssignments     MentorAssignment[]
+  mentorFiles           MentorFile[]
+  mentorChangeRequests  MentorChangeRequest[]
   filteringResults      FilteringResult[]
   awardEligibilities    AwardEligibility[]
   awardVotes            AwardVote[]
@@ -1270,7 +1273,7 @@ model TeamMember {
 
 model MentorAssignment {
   id        String @id @default(cuid())
-  projectId String @unique // One mentor per project
+  projectId String // Team can have multiple mentors; uniqueness enforced via composite below
   mentorId  String // User with MENTOR role or expertise
 
   // Assignment tracking
@@ -1278,6 +1281,9 @@ model MentorAssignment {
   assignedAt DateTime               @default(now())
   assignedBy String? // Admin who assigned
 
+  // Per-assignment email idempotency: stamped once the assignment notification email is sent.
+  notificationSentAt DateTime?
+
   // AI assignment metadata
   aiConfidenceScore   Float?
   expertiseMatchScore Float?
@@ -1304,11 +1310,47 @@ model MentorAssignment {
   milestoneCompletions MentorMilestoneCompletion[]
   messages             MentorMessage[]
   files                MentorFile[]
+  changeRequests       MentorChangeRequest[]       @relation("MentorChangeRequestTarget")
 
+  @@unique([projectId, mentorId])
+  @@index([projectId])
   @@index([mentorId])
   @@index([method])
 }
 
+// =============================================================================
+// MENTOR CHANGE REQUESTS
+// =============================================================================
+
+enum MentorChangeRequestStatus {
+  PENDING
+  RESOLVED
+  DISMISSED
+}
+
+model MentorChangeRequest {
+  id                 String                    @id @default(cuid())
+  projectId          String
+  targetAssignmentId String? // Optional: a specific co-mentor the request is about
+  requestedByUserId  String?
+  reason             String                    @db.Text
+  status             MentorChangeRequestStatus @default(PENDING)
+  resolvedByUserId   String?
+  resolvedAt         DateTime?
+  resolutionNote     String?                   @db.Text
+  createdAt          DateTime                  @default(now())
+  updatedAt          DateTime                  @updatedAt
+
+  project          Project           @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  targetAssignment MentorAssignment? @relation("MentorChangeRequestTarget", fields: [targetAssignmentId], references: [id], onDelete: SetNull)
+  requestedBy      User?             @relation("MentorChangeRequester", fields: [requestedByUserId], references: [id], onDelete: SetNull)
+  resolvedBy       User?             @relation("MentorChangeResolver", fields: [resolvedByUserId], references: [id])
+
+  @@index([projectId])
+  @@index([status])
+  @@index([targetAssignmentId])
+}
+
 // =============================================================================
 // FILTERING ROUND SYSTEM
 // =============================================================================
@@ -2449,7 +2491,8 @@ model AssignmentIntent {
 
 model MentorFile {
   id                 String  @id @default(cuid())
-  mentorAssignmentId String
+  projectId          String // Primary access scope: files belong to the team
+  mentorAssignmentId String? // Nullable audit FK: which assignment uploaded; survives mentor drop
   uploadedByUserId   String
 
   fileName    String
@@ -2468,13 +2511,15 @@ model MentorFile {
   createdAt DateTime @default(now())
 
   // Relations
-  mentorAssignment MentorAssignment          @relation(fields: [mentorAssignmentId], references: [id], onDelete: Cascade)
+  project          Project                    @relation(fields: [projectId], references: [id], onDelete: Cascade, onUpdate: Cascade)
+  mentorAssignment MentorAssignment?          @relation(fields: [mentorAssignmentId], references: [id], onDelete: SetNull)
   uploadedBy       User                       @relation("MentorFileUploader", fields: [uploadedByUserId], references: [id])
   promotedBy       User?                      @relation("MentorFilePromoter", fields: [promotedByUserId], references: [id])
   promotedFile     ProjectFile?               @relation("PromotedFromMentorFile", fields: [promotedToFileId], references: [id], onDelete: SetNull)
   comments         MentorFileComment[]
   promotionEvents  SubmissionPromotionEvent[]
 
+  @@index([projectId])
   @@index([mentorAssignmentId])
   @@index([uploadedByUserId])
 }