fix: cascade forced retention when sharing an older conversation

Creating or updating a shared link computed a capped expiry for the
SharedLink itself but never converted the source conversation, so under
forced ephemeral retention sharing an older permanent chat left it
expiredAt: null and visible indefinitely after the public link expired,
unlike every other write path that converts a touched permanent chat.

Run applyForcedRetention on the source conversation after the share is
created/updated, converting it and its messages and capping its shares;
a no-op outside forced retention.

api/server/routes/__tests__/share.spec.js

@@ -81,6 +81,7 @@ jest.mock('~/models', () => ({
   getSharedLink: jest.fn(),
   getSharedLinkFile: jest.fn(),
   backfillSharedLinkFiles: jest.fn(),
+  applyForcedRetention: jest.fn(),
   getRoleByName: jest.fn(),
 }));
 
@@ -123,6 +124,7 @@ const {
   updateSharedLink,
   getSharedLinkFile,
   backfillSharedLinkFiles,
+  applyForcedRetention,
   getRoleByName,
 } = require('~/models');
 const shareRouter = require('../share');
@@ -341,6 +343,50 @@ describe('share routes', () => {
     expect(createSharedLink).not.toHaveBeenCalled();
   });
 
+  it('converts the source conversation under forced retention when creating a share', async () => {
+    mockGetSharedLinkExpiration.mockResolvedValue(activeExpiration);
+    createSharedLink.mockResolvedValue({ _id: 'link-123', shareId: 'share-123' });
+
+    const response = await request(buildApp({ retentionMode: RetentionMode.EPHEMERAL }))
+      .post('/api/share/convo-123')
+      .send({ targetMessageId: 'msg-123' });
+
+    expect(response.status).toBe(200);
+    expect(applyForcedRetention).toHaveBeenCalledWith(
+      { userId: 'user-123', interfaceConfig: { retentionMode: RetentionMode.EPHEMERAL } },
+      { conversationId: 'convo-123' },
+      expect.objectContaining({ context: expect.any(String) }),
+    );
+  });
+
+  it('does not convert the source conversation when the share is not created', async () => {
+    mockGetSharedLinkExpiration.mockResolvedValue(activeExpiration);
+    createSharedLink.mockResolvedValue(null);
+
+    const response = await request(buildApp({ retentionMode: RetentionMode.EPHEMERAL }))
+      .post('/api/share/convo-123')
+      .send({ targetMessageId: 'msg-123' });
+
+    expect(response.status).toBe(404);
+    expect(applyForcedRetention).not.toHaveBeenCalled();
+  });
+
+  it('converts the source conversation under forced retention when updating a share', async () => {
+    mongoose.models.SharedLink.findOne.mockReturnValue(lean({ conversationId: 'convo-123' }));
+    mockGetSharedLinkExpiration.mockResolvedValue(activeExpiration);
+    updateSharedLink.mockResolvedValue({ _id: 'link-456', shareId: 'share-456' });
+
+    await request(buildApp({ retentionMode: RetentionMode.EPHEMERAL }))
+      .patch('/api/share/share-123')
+      .send({ snapshotFiles: false });
+
+    expect(applyForcedRetention).toHaveBeenCalledWith(
+      { userId: 'user-123', interfaceConfig: { retentionMode: RetentionMode.EPHEMERAL } },
+      { conversationId: 'convo-123' },
+      expect.objectContaining({ context: expect.any(String) }),
+    );
+  });
+
   it('rejects new shares for expired conversations in all retention mode', async () => {
     mockGetSharedLinkExpiration.mockResolvedValue(expiredExpiration);
     createSharedLink.mockResolvedValue({ _id: 'link-123', shareId: 'share-123' });

api/server/routes/share.js

@@ -32,6 +32,7 @@ const {
   getSharedLink,
   getSharedLinkFile,
   backfillSharedLinkFiles,
+  applyForcedRetention,
   getRoleByName,
 } = require('~/models');
 const { getStrategyFunctions } = require('~/server/services/Files/strategies');
@@ -66,6 +67,18 @@ const resolveSharedLinkExpiration = (req, conversationId) =>
     },
   );
 
+/**
+ * Converts the shared source conversation (and its messages) under forced (ephemeral)
+ * retention, so sharing an older permanent chat does not leave it visible and non-expiring
+ * after the public link itself expires; a no-op outside forced retention.
+ */
+const enforceForcedRetention = (req, conversationId, context) =>
+  applyForcedRetention(
+    { userId: req?.user?.id, interfaceConfig: req?.config?.interfaceConfig },
+    { conversationId },
+    { context },
+  );
+
 /**
  * Shared messages
  */
@@ -441,6 +454,11 @@ router.post(
       );
       if (created) {
         await grantCreationPermissions(created._id, req.user.id, grantPublic, expiredAt);
+        await enforceForcedRetention(
+          req,
+          req.params.conversationId,
+          'POST /api/share/:conversationId',
+        );
         res.status(200).json(created);
       } else {
         res.status(404).end();
@@ -483,6 +501,9 @@ router.patch('/:shareId', requireJwtAuth, configMiddleware, async (req, res) =>
       if (updatedShare._id && expiredAt !== undefined) {
         await updateSharedLinkPermissionsExpiration(updatedShare._id, expiredAt);
       }
+      if (existing?.conversationId) {
+        await enforceForcedRetention(req, existing.conversationId, 'PATCH /api/share/:shareId');
+      }
       res.status(200).json(updatedShare);
     } else {
       res.status(404).end();