diff --git a/backend/__tests__/unit/controllers/messageController.test.js b/backend/__tests__/unit/controllers/messageController.test.js
index eaafe8393a..d17a8fd63c 100644
--- a/backend/__tests__/unit/controllers/messageController.test.js
+++ b/backend/__tests__/unit/controllers/messageController.test.js
@@ -70,6 +70,33 @@ describe('messageController', () => {
       expect(res.status).toHaveBeenCalledWith(400);
     });
 
+    it.each(['2019-02-30', '+002026-01-01T00:00:00.000Z', '1900-02-29', '2026-04-31', '+078915-01-01T00:00:00.000Z', '0000-01-01T00:00:00Z', 'garbage', ['2026-01-01', '2026-01-02']])(
+      'rejects invalid pagination timestamp %j without querying either message store', async (before) => {
+        PGMessage.findByPodId.mockClear();
+        MongoMessage.find.mockClear();
+        const res = { status: jest.fn().mockReturnThis(), json: jest.fn() };
+        await messageController.getMessages({ params: { podId: 'p1' }, query: { before }, user: { id: 'u1' } }, res);
+        expect(res.status).toHaveBeenCalledWith(400);
+        expect(PGMessage.findByPodId).not.toHaveBeenCalled();
+        expect(MongoMessage.find).not.toHaveBeenCalled();
+      },
+    );
+
+    it.each([
+      ['2024-02-29', '2024-02-29T00:00:00.000Z'],
+      ['2026-10-24T12:30:15.123Z', '2026-10-24T12:30:15.123Z'],
+      ['2026-10-24T12:30:15+02:00', '2026-10-24T10:30:15.000Z'],
+    ])('keeps a valid calendar cursor %s on the PG path', async (before, canonical) => {
+      Pod.findById.mockResolvedValue({ members: ['u1'] });
+      PGMessage.findByPodId.mockResolvedValue([]);
+      MongoMessage.find.mockClear();
+      const res = { status: jest.fn().mockReturnThis(), json: jest.fn() };
+      await messageController.getMessages({ params: { podId: 'p1' }, query: { before }, user: { id: 'u1' } }, res);
+      expect(PGMessage.findByPodId).toHaveBeenLastCalledWith('p1', 50, canonical);
+      expect(MongoMessage.find).not.toHaveBeenCalled();
+      expect(res.json).toHaveBeenCalledWith([]);
+    });
+
     it('returns 404 if pod not found', async () => {
       Pod.findById.mockResolvedValue(null);
       const req = { params: { podId: 'p1' }, query: {}, user: { id: 'u1' } };
diff --git a/backend/__tests__/unit/models/Message.test.js b/backend/__tests__/unit/models/Message.test.js
index 0bc02ef248..c70cdc376b 100644
--- a/backend/__tests__/unit/models/Message.test.js
+++ b/backend/__tests__/unit/models/Message.test.js
@@ -71,6 +71,29 @@ describe('Message Model Tests', () => {
     expect(savedMessage.updatedAt).toBeDefined();
   });
 
+  it.each(['+078915-01-01T00:00:00.000Z', '0000-12-31T23:59:59.999Z'])(
+    'rejects nonportable createdAt %s before persistence', async (createdAt) => {
+      await expect(Message.create({ podId: testPod._id, userId: testUser._id,
+        content: 'Must not poison pagination', createdAt })).rejects.toMatchObject({
+        name: 'ValidationError', errors: { createdAt: expect.anything() },
+      });
+      expect(await Message.countDocuments({ podId: testPod._id })).toBe(0);
+    },
+  );
+
+  it('accepts four-digit-year timestamp boundaries without changing them', async () => {
+    for (const createdAt of ['0001-01-01T00:00:00.000Z', '9999-12-31T23:59:59.999Z']) {
+      const message = new Message({ podId: testPod._id, userId: testUser._id, content: 'Boundary', createdAt });
+      await message.save();
+      const reloaded = await Message.findById(message._id).lean();
+      expect(reloaded.createdAt.toISOString()).toBe(createdAt);
+      expect(String(reloaded.podId)).toBe(String(testPod._id));
+      expect(String(reloaded.userId)).toBe(String(testUser._id));
+      expect(reloaded.content).toBe('Boundary');
+      expect(reloaded.messageType).toBe('text');
+    }
+  });
+
   it('should not save a message without required fields', async () => {
     // Test missing podId
     const messageWithoutPodId = new Message({
diff --git a/backend/controllers/messageController.ts b/backend/controllers/messageController.ts
index 56230608ef..397f174e0d 100644
--- a/backend/controllers/messageController.ts
+++ b/backend/controllers/messageController.ts
@@ -85,7 +85,31 @@ const normalizeMongo = (m: Record<string, unknown>): NormalizedMessage => {
 exports.getMessages = async (req: AuthRequest, res: Response): Promise<void> => {
   try {
     const { podId } = req.params;
-    const { before } = req.query as { before?: string };
+    let { before } = req.query as { before?: string };
+    // Legacy Mongo rows can still supply an extended-year cursor. Refuse it
+    // before PG errors and the whole request falls back to Mongo.
+    if (before !== undefined) {
+      // Date.parse normalizes February 30 and accepts six-digit signed
+      // years that PG rejects. Validate calendar fields before parsing.
+      const match = typeof before === 'string'
+        ? /^(\d{4})-(\d{2})-(\d{2})(?:T(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d(?:\.\d{1,3})?(?:Z|[+-](?:[01]\d|2[0-3]):[0-5]\d))?$/.exec(before)
+        : null;
+      const year = Number(match?.[1]);
+      const month = Number(match?.[2]);
+      const day = Number(match?.[3]);
+      const leap = year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+      const days = [31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+      const cursor = match ? new Date(before) : null;
+      if (!cursor || !Number.isFinite(cursor.getTime()) || year < 1
+        || month < 1 || month > 12 || day < 1 || day > days[month - 1]
+        || cursor.getUTCFullYear() < 1 || cursor.getUTCFullYear() > 9999) {
+        res.status(400).json({ msg: 'before must be a valid ISO date or timestamp with a year from 0001 to 9999' });
+        return;
+      }
+      // Send one portable representation to PG, including for offset inputs.
+      before = cursor.toISOString();
+    }
+
     // Clamp the page size [1, 200]. Unbounded `limit` let a caller ask for
     // millions of rows → OOM (both the PG and Mongo read paths below). Mirrors
     // the postController.getPosts clamp pattern.
diff --git a/backend/models/Message.ts b/backend/models/Message.ts
index 9af8e046aa..2c66dda65d 100644
--- a/backend/models/Message.ts
+++ b/backend/models/Message.ts
@@ -53,7 +53,14 @@ const MessageSchema = new Schema<IMessage>({
   authorKind: { type: String, enum: ['kernel', null], default: null },
   payload: { type: Schema.Types.Mixed },
   metadata: { type: Schema.Types.Mixed },
-  createdAt: { type: Date, default: Date.now },
+  // Client pagination and the PG timestamp parser require four-digit years.
+  // JS/Mongo accept extended ISO years (e.g. +078915), which PG rejects when
+  // a client sends the stored value back as its pagination cursor.
+  createdAt: {
+    type: Date, default: Date.now, required: true,
+    min: new Date('0001-01-01T00:00:00.000Z'),
+    max: new Date('9999-12-31T23:59:59.999Z'),
+  },
   updatedAt: { type: Date, default: Date.now },
   // New Mongo-only writes start pending. The post-save hook stamps a server
   // commit marker after the insert is acknowledged; a crash before that stamp