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Architecture

This repository sits at the centre of the COMEBACKHERE protocol and orchestrates three sibling projects:

  • Smart contracts — Soroban contracts (invoice, treasury, compliance).
  • Backend API — Node/Express service that fronts the contracts.
  • Frontend UI — React/Vite app used by merchants, payers, and admins.

Each layer has two source trees in this repository, plus CI jobs that pull a third copy from upstream. This document explains which tree to target when contributing.

Canonical trees (where changes go)

The active source of truth for each layer lives in a tree with the COMEBACKHERE- prefix inside this repository:

Layer Canonical tree Why
Contracts (Rust) COMEBACKHERE-contracts/ cargo test --manifest-path COMEBACKHERE-contracts/Cargo.toml is run by make test and by .github/workflows/ci-contracts.yml. ABI snapshots in abis/ are generated from this workspace.
Backend (Node) comebackhere-backend/ Referenced by .github/workflows/ci.yml for npm ci, tsc --noEmit, npm run lint, npm run build.
Frontend (React) comebackhere-frontend/ Same as backend — the ci.yml working-directory points here.

New feature work, bug fixes, and contract changes should target these three directories by default — they're the only ones with a dedicated, contract-specific CI workflow.

Mirrored trees (older in-tree copies)

The repository also contains a parallel set of directories without the prefix:

  • contracts/ and backend/ and frontend/

These are in-tree copies of the canonical sources at earlier points in time. They are kept because:

  • Process docs reference them by path. docs/error-codes.md calls out contracts/invoice/src/lib.rs as the source of InvoiceError; that file still lives here.
  • They give reviewers a familiar path while the migration to the COMEBACKHERE-* trees completes.

These trees are valid PR targets, but they have a gap in coverage: only the ci-*.yml workflows that match their files run on a PR touching them. There is no independent cargo test for contracts/Cargo.toml or backend/Cargo.toml, and no independent frontend build for frontend/. So a green PR here will not, by itself, prove the change works against the toolchain pinned in the canonical workspace.

If your change is brand-new work, target the COMEBACKHERE-* tree to inherit full CI coverage. If your change is intentionally narrow (a doc tweak, a small Rust fix in a file the CI happens to cover), the mirrored tree is fine.

CI checkout behaviour

Some CI workflows re-check the canonical trees out from upstream rather than using the in-tree copies:

  • ci-contracts.yml, ci-abi-snapshots.yml, ci-abi-metadata.yml, ci-post-deploy-verify.yml, and ci-coverage.yml do actions/checkout of WHEELBACK/COMEBACKHERE-contracts into the local COMEBACKHERE-contracts/ path.
  • The local COMEBACKHERE-contracts/ checkout in this repository exists so that make update-abi-snapshots and scripts/check_abi_snapshot_hygiene.sh work locally without a separate clone.
  • A consumer running on a developer's machine can equivalently clone COMEBACKHERE-contracts as a sibling directory; scripts/generate_abi_metadata.sh looks for both locations.

Other top-level paths

  • abis/ — committed ABI metadata (invoice.json, treasury.json, compliance.json). Generated from COMEBACKHERE-contracts/ via make update-abi-snapshots.
  • scripts/ — Bash + Python helpers for ABI generation, snapshot hygiene, deployment, and backend env validation.
  • docs/ — error codes, API reference, deployment guides, the ABI snapshot workflow, and other process docs.
  • .github/workflows/ — CI jobs.

Local development layout

A working clone for end-to-end development looks like this (see docs/dev-environment.md for full setup):

~/comebackhere/
  ├── COMEBACKHERE-contracts/   # canonical contracts
  ├── COMEBACKHERE/             # this repository
  ├── comebackhere-backend/     # canonical backend
  └── comebackhere-frontend/    # canonical frontend

When working inside this repository alone, the in-tree COMEBACKHERE-contracts/ checkout acts as the canonical contracts tree; the sibling-clone step is optional for backend/frontend contributors.

Invoice state machine

The invoice contract (COMEBACKHERE-contracts/contracts/invoice/src/lib.rs, mirrored at contracts/invoice/src/lib.rs) is the source of truth every other layer reads from: backend status displays, the indexer, and both frontend apps all ultimately derive their view of an invoice from this state machine. The diagram below shows every InvoiceStatus value and the function whose call transitions an invoice into it. Any transition not shown here is illegal and the calling function returns an InvalidStateTransition / NotPending style error (see docs/error-codes.md for the exact variant and code per contract).

stateDiagram-v2
    [*] --> Pending: create_invoice

    Pending --> Paid: mark_paids / pay_invoice
    Pending --> Expired: batch_expire
    Pending --> Cancelled: cancel_invoiced / cancel_invoice

    Paid --> RefundRequested: request_refund
    Paid --> RefundRequested: cancel_invoiced / cancel_invoice

    RefundRequested --> Released: release_escrow (after grace window)

    Expired --> [*]
    Cancelled --> [*]
    Released --> [*]
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Notes on edges that are deliberately absent from this diagram:

  • Paid is never re-entered. Once an invoice leaves Pending, no function transitions it back to Paid. In particular, mark_paids guards against being called on an invoice that is RefundRequested, Released, Cancelled, or Expired, so a stale or replayed payment confirmation can never silently override a refund already in progress.
  • RefundRequested, Released, Cancelled, and Expired are terminal with respect to payment and cancellation — cancel_invoiced, request_refund, and mark_paids all reject calls made once an invoice has reached one of these states.
  • release_escrow is time-gated, not just state-gated: it additionally requires ledger.timestamp() >= invoice.created_at + grace_window.

Further reading