feat: `DELETE /cards/:id` returns 204 No Content on success but has no cascade behavior defined — deleting a card that is someone's default leaves them with no default card and no recovery path

[divyanshim27]

🐛 Problem Statement

The README's API error table documents:

DELETE /:id → 404 { error: 'Card not found' } when card ID doesn't exist

But there is no documented behavior for deleting the user's default card. The Prisma schema has a isDefault boolean on each card, and the README states: "first card is auto-set as default."

If a user has 3 cards (Card A = default, Card B, Card C) and deletes Card A:

• No new default is automatically assigned
• The user's QR code (which presumably resolves to their default card) now points to null
• The PUT /:id/default endpoint can be used to fix this, but the user has no indication anything went wrong
• A receiver who scans the QR before the user notices sees a broken profile

Proposed Fix

In apps/backend/src/routes/cards.ts, add a post-delete cascade that automatically promotes the oldest remaining card to default when the deleted card was the default:

// apps/backend/src/routes/cards.ts — inside DELETE /:id handler

const deletedCard = await prisma.card.findUnique({
  where: { id: params.id, userId: request.user.id }
});

if (!deletedCard) {
  return reply.status(404).send({ error: 'Card not found' });
}

await prisma.card.delete({ where: { id: params.id } });

// If the deleted card was the default, auto-promote the next oldest card
if (deletedCard.isDefault) {
  const nextCard = await prisma.card.findFirst({
    where: { userId: request.user.id },
    orderBy: { createdAt: 'asc' },
  });

  if (nextCard) {
    await prisma.card.update({
      where: { id: nextCard.id },
      data: { isDefault: true },
    });
  }
}

return reply.status(204).send();

Also update the API response for this case to return 200 with a body describing the auto-promotion (rather than 204 No Content) so clients can update their state:

{
  "message": "Card deleted. Card 'My Professional Card' has been set as your new default."
}

Update the error table in README.md to document this behavior.

Files to Modify

File	Change
apps/backend/src/routes/cards.ts	Add default card cascade logic in DELETE handler
README.md	Document auto-promotion behavior in error/response table

Suggested labels: bug, backend, level: intermediate

I would like to work on this. Could you please assign it to me?

[github-actions]

Hi @divyanshim27,

Thanks for opening this issue.

Please reply with one of the following areas so the issue can be routed to the appropriate team member:

- /backend
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[github-actions]

👋 Thanks for opening your first issue, @divyanshim27!

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[divyanshim27]

Hey @maintainers,
Please assign it to me under GSSoC 2026.
/claim /assign /claim-assignment