feat: Implement Skywire Decentralized Exchange (Exchange Market & Client)

[mrpalide]

Did you run make format && make check? Yes

Overview
This PR is the Skywire half of the SkyDEX decentralized-exchange ecosystem: two thin visor apps — skydex-market and skydex-client — that carry the exchange over a Skywire dmsg transport using the visor's app networking. The exchange engine itself — the dmsg protocol, SQLite state, escrow, background jobs, local-signed blockchain settlement, the operator UI, and the React trading client — now lives in the skycoin repo (src/skydex/*, cmd/skydex-*) and carries zero skywire dependency. See the companion PR skycoin/skycoin#. This mirrors how skywire wraps skycoin-web: domain logic in skycoin, networking as a drop-in skywire reconfiguration.

The market sells SKY and any operator-added Skycoin fibercoin — each coin is add/edit/enable/disable/delete-able with its own fullnode + escrow hot wallet — against external UTXO coins (BTC/LTC) or another fibercoin. Users are identified solely by their Skywire public key. Payments are auto-verified against the recipient wallet — no transaction hash required from users: sell-coin/fibercoin transfers by sender address + time window + fixed amount, external UTXO payments (BTC/LTC) by a unique non-round amount + time window. Sell-coin delivery and refunds are signed locally from an operator seed and broadcast via that coin's Skycoin-family node (the node's wallet API is never used).

Repo split

• skycoin/skycoin (companion PR) — src/skydex/{protocol,message,db,chain,jobs,walletaddr,server,market} (the engine) + cmd/skydex-market / cmd/skydex-client (standalone TCP reference commands, operator/auth UI, React client). No skywire import.
• skywire (this PR) — cmd/apps/skydex-{market,client}: the transport wrapper that Listens/Dials over appnet dmsg, injects the authenticated public key as identity, and hands a net.Listener / net.Conn to the engine. Plus app registration in config-gen and the two-visor dmsg-mesh E2E.

Implementation Status

✅ In this PR (skywire — transport wrapper)

• Project Structure: cmd/apps/skydex-client and cmd/apps/skydex-market, registered in the
  merged skywire binary and emitted in generated visor configs (routing ports 8050/8051; --addr/
  --port on both, --market-pk/--market-port on the client).
• Transport wrapper (market): Listens on appnet.TypeDmsg via the visor and injects each
  client's authenticated dmsg remote public key as the identity (server.IdentifyFunc), then
  delegates to the engine's Run. No bespoke dmsg server — uses app networking.
• Transport wrapper (client): dials the market's public key over dmsg (MarketDialer) and
  hands the framed connection to the engine.
• Visor bridges: internal/skydex-{market,client}/app (the app.Client wrappers) and the
  engine Host / MarketDialer adapters — operator OTP → visor app list, market identity → visor PK.
• Two-visor dmsg-mesh E2E (internal/skydex-e2e, scripted chain) driving the skycoin engine
  over a real in-process dmsg mesh; plus a guided livenet-tagged live harness.
• go.mod imports the skycoin engine (see Merge sequencing).

✅ In the companion skycoin PR (the engine — no skywire dependency)

• Communication Layer (dmsg protocol): JSON message protocol (src/skydex/protocol) — register,
  get_currencies, get_products, create_listing, buy_product, cancel_listing, cancel_order, get_orders,
  get_order_status, get_listings; framed with src/skydex/message (a copy of skywire's
  pkg/skychat/message). The server is transport-agnostic: Accept(ctx, net.Listener, IdentifyFunc)
  • ServeConn(conn, identity); single-session enforcement per identity.
• Market Backend: standalone (TCP) reference command + SQLite layer (src/skydex/db) with
  auto-migrations — 8 tables + full CRUD, thread-safe; default config (commission, confirmations,
  trade limits, timeouts, ban rules, per-coin explorers, sell-coin registry).
• Operator UI (served on :8050): configuration (commission rate/floor/cap, confirmations,
  min/max trade size, ban rules), the sell-coin registry (add/edit/enable/disable/delete SKY +
  fibercoins, each with its own node URL, escrow seed/address and confirmation depth), per-coin
  explorer enable/disable, and monitoring (products, orders, bans, commission), behind a localhost
  operator API gated by a one-time code the app publishes to its host (the visor app list over
  skywire). The UI is parameterized by a 3-method Host (Log / PublishOTP / PubKey).
• Multi sell-coin registry (fibercoins): sell_coins table (SKY is the seeded, editable
  default), a per-symbol chain router, coin-generic wire/DB/UI. One registered address receives
  every fibercoin a user buys.
• Fibercoin-to-fibercoin trades: the payment currency may itself be a sell coin, verified on
  that coin's node by sender + window + fixed amount; external UTXO coins keep the unique
  non-round amount.
• Background Jobs — 7 jobs under a Runner: Expiry Handler, Listing Checker, Escrow Checker,
  Return Scheduler (immediate refund), Ban Manager, Cleanup Job, Escrow Audit (per sell coin).
• Blockchain Integration (src/skydex/chain): local-signed sell-coin settlement (read UTXOs
  /api/v1/outputs, sign in-process via src/coin+src/cipher+src/transaction, broadcast via
  /injectTransaction); deposit & payment verification by address + window + exact amount; pluggable
  per-coin explorer adapters (Esplora live-validated for BTC/LTC). Live-verified on SKY mainnet.
• Commission (sell coin) — clamp(amount × rate%, min, cap), folded into the seller's deposit.
• Cancel flows — buyer cancel-order (freeze violation) and seller cancel-offer (immediate refund).
• Client (React + Vite + Bootstrap SPA), Skywire-themed, embedded via embed.FS in
  cmd/skydex-client: connect gate → Market / My Orders / My Listings / Settings; sell-coin +
  payment-currency selection; live get_order_status polling (confirmations/tx-hash, commission
  breakdown, cancel buttons).
• Hardening — per-coin wallet-address validation (Skycoin/BTC/LTC), session idle timeout,
  escrow/DB consistency audit, operator-configurable confirmations and trade size.
• Full two-party live E2E (livenet-tagged) — deposit → buy → pay → deliver against the live
  SKY node + Esplora, local-signed SKY delivery, commission retained; on-chain verified.
• Testing — unit/integration for protocol transport, server handlers, jobs, chain (httptest +
  livenet live checks), the sell-coin registry, fibercoin-payment routing, and both apps' HTTP APIs.

🚧 TODO / Pending

• More payment coins (post-feedback) — BCH / DOGE / DASH are already wired through the Esplora
  adapter but not yet validated end-to-end; they'll be enabled after feedback + testing.
  Account/token chains (USDT ERC-20/TRC-20, ETH) need per-contract endpoints and are future work.
  (XMR intentionally unsupported — not verifiable by address.)
• Standalone auth — the skycoin standalone (non-skywire) build currently identifies a peer by
  its TCP remote address; a real standalone auth (TLS client cert / blockchain login) is a follow-up.
  Over skywire the identity is the authenticated dmsg public key (already in place).

Notes

• The exchange engine lives in skycoin and is imported here as a drop-in; skywire supplies only the
  dmsg transport + identity injection + config-gen registration.
• Sell-coin spend path signs locally; the coin's node is used only for reads + broadcast, and its
  wallet API is never touched (the escrow seed stays in-process).
• The market sells SKY and any Skycoin fibercoin side by side; the payment leg can be an external
  UTXO coin (BTC/LTC) or another fibercoin (fixed amount, verified on its node).
• Commission is charged in the sell coin (a Coin-Hours/SCH fee, and SCH-for-BTC/LTC trading, were
  considered and dropped as low-value/uncontrollable).
• Database uses modernc.org/sqlite (pure-Go, CGO-free — matches the repo's CGO_ENABLED=0
  static, cross-compiled builds); all timestamps stored as UTC.
• All UI text is English; privacy-first (no PII; identity is the Skywire public key; trade data
  auto-deleted after 3 days).
• Payment verification is by amount + address + time window in the recipient wallet's recent
  transactions — no user-submitted transaction hashes.

[0pcom]

@mrpalide note that there are a few repos that you might want to look at which already did a lot in this general direction. I think they were designed for a centralized model, but might still be relevant.

https://github.com/skycoin/skycoin-exchange
https://github.com/SkycoinPro/coin-hour-bank
https://github.com/SkycoinPro/coin-hour-bank-wallet