feat(gateway): multi-merchant support — sub-accounts under a single publishable key

[aguilar1x]

Context

Today one publishable key maps to exactly one merchant. Platforms and marketplaces that want to onboard many sub-merchants (each with isolated escrow settlement) have no way to integrate Connect without provisioning a separate key/gateway config per sub-merchant.

Scope

• A merchantId (or sub-account) concept in the gateway's key model: one platform-level pk_/sk_ pair can create sessions scoped to a specific sub-merchant.
• Isolated escrow settlement and webhook delivery per sub-merchant — a platform never sees another sub-merchant's funds mixed in.
• Admin-facing listing of sub-merchants and their aggregate volume, exposed via the gateway API.

Acceptance criteria

• Creating a session with a merchantId routes settlement to that sub-merchant only.
• Webhooks for one sub-merchant's escrow never reach another sub-merchant's configured endpoint.
• A platform can list its sub-merchants and per-sub-merchant volume via the gateway API.

[OpadijoIdris]

i understand the scope and the acceptance criteria, kindly assign

[AbuJulaybeeb]

hi maintainer, i am a Full-Stack and web3 Developer, with 4+ years of experience. I have carefully read and understand the description of this issue, and i would like to take on this issue

[fabicabvq06]

Hello maintainers,


I'd like to work on this issue.


I enjoy understanding how systems fit together, improving workflows, and contributing solutions that are reliable and maintainable. After reviewing the issue, I believe I can help implement a clean solution while following the project's existing patterns and standards.


If assigned, I'll keep the discussion updated and submit a well-tested PR.


Thanks for your time and consideration.

[grantfox-oss]

🦊 GrantFox — @fabicabvq06 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #44)
2. Your PR will be reviewed by the PACTO-LAT maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@fabicabvq06's PR #49 was approved and merged by @aguilar1x.

🏆 @fabicabvq06: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (169 total points). Track your full progress on GrantFox.

👏 Great work, @fabicabvq06! Keep contributing to PACTO-LAT.