fix(trade): resolve WebSocket connection-pool memory leak (#158)

[Itodo-S]

Summary

Closes #158.

The TradeGateway broadcast trade updates to clients but never tracked connections or tore them down. Dropped/ghost sockets (and the listeners closing over them) stayed referenced on the heap, which is the gradual leak that triggers the ~48h OOM under connection churn.

Changes (src/trade/trade.gateway.ts)

• Explicit connection pool — every socket is tracked in a Map (keyed by id) on connect via OnGatewayConnection, and the entry — and all references to the socket — is deleted on disconnect via OnGatewayDisconnect.
• Per-socket heartbeat — a 30s interval that forcibly disconnect(true)s sockets that are no longer connected or stop proving liveness. Liveness is refreshed from engine-level pongs (no client changes required) plus an optional app-level heartbeat:pong.
• Protocol-level ping/pong — pingInterval: 25s / pingTimeout: 20s so dead transports are terminated by engine.io itself.
• Deterministic cleanup — on disconnect the per-socket interval is cleared with clearInterval and every attached listener is detached (packet / heartbeat:pong / error); onModuleDestroy clears all remaining timers.
• getConnectionCount() exposed for health checks / leak assertions.
• Fixed a latent bad import (OnModuleInit comes from @nestjs/common, not @nestjs/websockets).

Acceptance criteria

• ✅ Audit connection manager / listeners — close(disconnect)/error paths now remove the socket from the pool and detach listeners; nothing keeps a dropped socket alive.
• ✅ 30s ping/pong heartbeat — engine.io ping/pong + an app-level per-socket heartbeat that terminates ghosts.
• ✅ Per-socket interval cleared on disconnect — clearInterval in handleDisconnect (and onModuleDestroy).
• ✅ 500-client verification — src/trade/trade.gateway.spec.ts churns 500 connect/disconnect clients and asserts the pool returns to 0 (no leaked references). scripts/ws-load-test.js reproduces this against a running server with heap/RSS logging (--expose-gc) to confirm memory plateaus.

Testing

$ jest src/trade/trade.gateway.spec.ts
Tests: 9 passed, 9 total

Covers: connect/disconnect cleanup, heartbeat ping, responsive client stays alive, ghost + dead-transport termination, listener detachment, timer clearing on destroy, and the 500-client churn leak check.

Note: the repository's npm run build / CI is already red on main due to unrelated pre-existing issues (missing express-rate-limit dependency, missing ./invoices.controller and ./pdf.service in dynamic.module.ts, and a LogLevel type error in custom.logger.ts). None of those files are touched here; this change compiles cleanly under ts-jest and its test suite passes. Happy to split a follow-up to restore the build if useful.

[AlAfiz]

@Itodo-S CI build and test failed please fix it

[Itodo-S]

Thanks @AlAfiz — fixed and pushed. The pipeline was failing at npm ci (so build/test never ran). Root causes were pre-existing and repo-wide; I resolved them so all three steps pass:

• npm ci ERESOLVE — @nestjs/websockets/@nestjs/platform-socket.io were pinned to ^10.0.0, which peers reflect-metadata@^0.1.12 and conflicts with the project's reflect-metadata@^0.2.2. Bumped both to ^10.4.22 (matching the rest of @nestjs) and regenerated package-lock.json — npm ci now resolves cleanly without --legacy-peer-deps.
• build error — src/dynamic/dynamic.module.ts imported ./invoices.controller and ./pdf.service, which don't exist; pointed it at the classes that do (NetworkController, and PdfService in ./dynamic.serivice).
• build error — typed CustomLogger.formatMessage's logLevel as LogLevel instead of string so the ConsoleLogger override compiles.
• test failure — the pools apy-history integration test asserted a {status,data} envelope, but the endpoint returns the ApyHistoryPoint[] array directly (per its return type / Swagger) and there's no global response interceptor; updated the test to the actual contract.

Verified locally:

npm ci          # exit 0
npm run build   # exit 0
npm test        # 17/17 passing