fix(couples): protect joined invites from cancellation

apps/api/src/domains/couples/repository.ts

@@ -33,6 +33,7 @@ export interface CoupleRepository {
   getState(userId: string): Promise<CoupleStateResponse>;
   create(userId: string, coupleId: string, inviteCode: string): Promise<Couple>;
   join(userId: string, inviteCode: string): Promise<Couple>;
+  cancelInvite(userId: string): Promise<void>;
   cancel(userId: string): Promise<void>;
   close(): Promise<void>;
 }
@@ -268,6 +269,42 @@ export class PostgresCoupleRepository implements CoupleRepository {
     });
   }
 
+  async cancelInvite(userId: string): Promise<void> {
+    await transaction(this.pool, async (client) => {
+      // Lock in the same order as join(): the caller's profile first, then the
+      // couple. A concurrent join therefore either completes first and makes
+      // this a safe no-op error, or observes that the invite no longer exists.
+      const profile = await profileForUpdate(client, userId);
+      if (!profile.couple_id) {
+        throw new CoupleError('not_paired', 'You do not have an invite to cancel', 400);
+      }
+
+      const coupleResult = await client.query<{ id: string }>(
+        'select id from couples where id = $1 for update',
+        [profile.couple_id],
+      );
+      if (!coupleResult.rows[0]) {
+        throw new CoupleError('not_paired', 'You do not have an invite to cancel', 400);
+      }
+
+      const members = await client.query<{ id: string }>(
+        'select id from profiles where couple_id = $1 for update',
+        [profile.couple_id],
+      );
+      if (members.rows.length > 1) {
+        throw new CoupleError('invite_already_joined', 'This invite has already been joined', 409);
+      }
+      if (members.rows.length !== 1 || members.rows[0]?.id !== userId) {
+        throw new CoupleError('not_paired', 'You do not have an invite to cancel', 400);
+      }
+
+      // At this point the couple has precisely the authenticated creator as a
+      // member. Removing it cannot delete paired data, and the foreign key
+      // clears the creator's couple_id while leaving sealed answers intact.
+      await client.query('delete from couples where id = $1', [profile.couple_id]);
+    });
+  }
+
   async close(): Promise<void> {
     await closeResolvedPool(this.pool, this.ownsPool);
   }

apps/api/src/domains/couples/routes.ts

@@ -50,4 +50,9 @@ export function registerCoupleRoutes(app: AuthenticatedApp, service: CoupleServi
     const result = await route(() => service.cancel(c.get('identity').id));
     return result.ok ? c.json(result.value) : c.json(result.body, result.status);
   });
+
+  app.delete('/v1/couple/invite', async (c) => {
+    const result = await route(() => service.cancelInvite(c.get('identity').id));
+    return result.ok ? c.json(result.value) : c.json(result.body, result.status);
+  });
 }

apps/api/src/domains/couples/service.ts

@@ -41,4 +41,9 @@ export class CoupleService {
     await this.repository.cancel(userId);
     return { success: true, couple_id: null };
   }
+
+  async cancelInvite(userId: string): Promise<CoupleMutationResponse> {
+    await this.repository.cancelInvite(userId);
+    return { success: true, couple_id: null };
+  }
 }

apps/api/src/domains/couples/types.ts

@@ -19,6 +19,7 @@ export type CoupleErrorCode =
   | 'invalid_invite_code'
   | 'couple_full'
   | 'not_paired'
+  | 'invite_already_joined'
   | 'invite_code_collision';
 
 export class CoupleError extends Error {

apps/api/test/couples.repository.integration.test.ts

@@ -68,6 +68,38 @@ describe.skipIf(!databaseUrl || !localDatabase)('PostgresCoupleRepository', () =
     expect((await pool.query('select count(*)::int as count from couples')).rows[0].count).toBe(0);
   });
 
+  it('cancels a waiting invite only for its creator', async () => {
+    const coupleId = 'bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb';
+    await repository.create(charlie, coupleId, 'WAIT2345');
+
+    await repository.cancelInvite(charlie);
+
+    await expect(repository.getState(charlie)).resolves.toEqual({ couple: null, partner: null, sealed_count: 0 });
+    expect((await pool.query('select count(*)::int as count from couples where id = $1', [coupleId])).rows[0].count).toBe(0);
+  });
+
+  it('never deletes a joined couple through the invite cancellation path', async () => {
+    const coupleId = 'cccccccc-cccc-4ccc-8ccc-cccccccccccc';
+    await repository.create(alice, coupleId, 'SAFE2345');
+    await repository.join(bob, 'SAFE2345');
+
+    const before = await pool.query<{ id: string; couple_id: string | null }>(
+      'select id, couple_id from profiles where id in ($1, $2) order by id',
+      [alice, bob],
+    );
+    await expect(repository.cancelInvite(alice)).rejects.toMatchObject({
+      code: 'invite_already_joined',
+      status: 409,
+    });
+
+    const after = await pool.query<{ id: string; couple_id: string | null }>(
+      'select id, couple_id from profiles where id in ($1, $2) order by id',
+      [alice, bob],
+    );
+    expect(after.rows).toEqual(before.rows);
+    expect((await pool.query('select count(*)::int as count from couples where id = $1', [coupleId])).rows[0].count).toBe(1);
+  });
+
   it('reports a solo answerer\'s sealed count before any couple exists', async () => {
     const pack = 'cccccccc-cccc-4ccc-8ccc-cccccccccccc';
     const solo = 'dddddddd-dddd-4ddd-8ddd-dddddddddddd';

apps/api/test/couples.routes.test.ts

@@ -4,6 +4,7 @@ import type { AuthIdentity } from '../src/auth.js';
 import type { CoupleRepository } from '../src/domains/couples/repository.js';
 import { registerCoupleRoutes } from '../src/domains/couples/routes.js';
 import { CoupleService } from '../src/domains/couples/service.js';
+import { CoupleError } from '../src/domains/couples/types.js';
 
 const identity: AuthIdentity = {
   id: '11111111-1111-4111-8111-111111111111',
@@ -25,6 +26,7 @@ function setup() {
       invite_code: inviteCode,
       created_at: '2026-08-27T00:00:00.000Z',
     })),
+    cancelInvite: vi.fn(async () => undefined),
     cancel: vi.fn(async () => undefined),
     close: vi.fn(async () => undefined),
   };
@@ -80,4 +82,28 @@ describe('couple routes', () => {
     expect(await response.json()).toEqual({ success: true, couple_id: null });
     expect(repository.cancel).toHaveBeenCalledWith(identity.id);
   });
+
+  it('cancels only the authenticated user\'s waiting invite on the dedicated route', async () => {
+    const { app, repository } = setup();
+    const response = await app.request('/v1/couple/invite', { method: 'DELETE' });
+    expect(response.status).toBe(200);
+    expect(await response.json()).toEqual({ success: true, couple_id: null });
+    expect(repository.cancelInvite).toHaveBeenCalledWith(identity.id);
+    expect(repository.cancel).not.toHaveBeenCalled();
+  });
+
+  it('does not turn a joined invite into relationship deletion', async () => {
+    const { app, repository } = setup();
+    vi.mocked(repository.cancelInvite).mockRejectedValueOnce(
+      new CoupleError('invite_already_joined', 'This invite has already been joined', 409),
+    );
+
+    const response = await app.request('/v1/couple/invite', { method: 'DELETE' });
+
+    expect(response.status).toBe(409);
+    expect(await response.json()).toEqual({
+      error: { code: 'invite_already_joined', message: 'This invite has already been joined' },
+    });
+    expect(repository.cancel).not.toHaveBeenCalled();
+  });
 });

apps/api/test/couples.service.test.ts

@@ -15,6 +15,7 @@ function repository(overrides: Partial<CoupleRepository> = {}): CoupleRepository
     getState: vi.fn(async () => ({ couple: null, partner: null, sealed_count: 0 })),
     create: vi.fn(async () => couple),
     join: vi.fn(async () => couple),
+    cancelInvite: vi.fn(async () => undefined),
     cancel: vi.fn(async () => undefined),
     close: vi.fn(async () => undefined),
     ...overrides,
@@ -61,4 +62,13 @@ describe('CoupleService', () => {
     expect(create).toHaveBeenCalledTimes(2);
     expect(create.mock.calls.every(([userId]) => userId === 'user-one')).toBe(true);
   });
+
+  it('uses the invite-only cancellation operation for a waiting creator', async () => {
+    const repo = repository();
+    const service = new CoupleService(repo);
+
+    await expect(service.cancelInvite('user-one')).resolves.toEqual({ success: true, couple_id: null });
+    expect(repo.cancelInvite).toHaveBeenCalledWith('user-one');
+    expect(repo.cancel).not.toHaveBeenCalled();
+  });
 });

apps/mobile/src/__tests__/lib/coupleApi.test.ts

@@ -12,12 +12,14 @@ describe("coupleApi", () => {
         await coupleApi.getState();
         await coupleApi.create();
         await coupleApi.join("ABCD2345");
+        await coupleApi.cancelInvite();
         await coupleApi.cancel();
 
         expect(request.mock.calls).toEqual([
             ["/v1/couple"],
             ["/v1/couple", { method: "POST", body: {} }],
             ["/v1/couple", { method: "POST", body: { invite_code: "ABCD2345" } }],
+            ["/v1/couple/invite", { method: "DELETE" }],
             ["/v1/couple", { method: "DELETE" }],
         ]);
     });

apps/mobile/src/lib/coupleApi.ts

@@ -24,4 +24,5 @@ export const coupleApi = {
         body: { invite_code: inviteCode },
     }),
     cancel: () => apiRequest<CoupleMutationResponse>("/v1/couple", { method: "DELETE" }),
+    cancelInvite: () => apiRequest<CoupleMutationResponse>("/v1/couple/invite", { method: "DELETE" }),
 };