Feature request: allow jam minting from existing in-app balance

[riseandshaheen]

Summary

The jam backend currently assumes minting happens only through an Ether Portal deposit carrying a jam.mint execution payload.

There is already a TODO in apps/jam-backend/src/index.js noting that we should support minting when a user already has ETH balance inside the app.

Current limitation

Today, the mint path is tied to this flow:

• user sends an Ether Portal deposit
• the deposit contains a jam.mint execution payload
• the backend checks the depositor's in-app balance after handling the deposit
• mint proceeds are distributed and a voucher is created

This means a user who already has sufficient internal balance in the rollup wallet still cannot mint unless they make another deposit with a mint request.

Why this matters

In a real-world flow, users may already hold ETH inside the application balance from prior deposits or prior activity.

Requiring a fresh deposit every time they want to mint:

• adds unnecessary friction
• creates a worse UX
• couples minting too tightly to the portal deposit flow
• prevents normal balance reuse inside the app

Requested behavior

Support minting a jam NFT using the user's existing in-app ETH balance, without requiring a new Ether Portal deposit at the same time.

Possible approaches:

• add a direct advance action such as jam.mint for normal input-box messages
• check the sender's existing internal wallet balance and, if sufficient, create the mint voucher and settle proceeds
• preserve the existing deposit-triggered mint flow as an optional fast path

Suggested acceptance criteria

• A user with sufficient internal balance can mint a jam NFT without making a fresh deposit
• The same validation rules still apply:
  • jam exists
  • NFT address is configured
  • balance is sufficient
• Successful mints still:
  • create the ERC1155 mint voucher
  • update jam stats
  • distribute mint proceeds to contributors
• Insufficient balance still returns a clear error report

Code reference

There is already a relevant TODO in:

• apps/jam-backend/src/index.js

The note indicates we should add a mint condition when the user already has in-app balance, rather than requiring minting only via an Ether Portal deposit.