obs: Implement structured health check endpoints with dependency status

[Xhristin3]

Problem Statement

The health check (api/src/health/health.controller.ts) only verifies database connectivity. There's no distinction between liveness (is the process alive?) and readiness (can it serve traffic?). There are no checks for WebSocket gateway health, memory usage, or upstream dependency status.

Evidence

// api/src/health/health.controller.ts — single endpoint
@Get()
async check(): Promise<HealthCheckResponseDto> {
  await this.healthCheckService.check([
    async () => this.databaseHealthIndicator.isHealthy("database"),
  ])
  return { status: "ok", timestamp: new Date().toISOString() }
}

Impact

Kubernetes cannot distinguish between a process that is alive but unable to serve traffic (e.g., DB connection lost temporarily) and a healthy process. Downtime detection is delayed.

Proposed Solution

1. Add GET /health/live — liveness probe (always returns ok if process is running)
2. Update GET /health — readiness probe (checks all dependencies: DB, memory threshold, event loop lag)
3. Add NestJS memory usage check and event loop lag check

Acceptance Criteria

• GET /health/live returns { status: "ok" } even if DB is down
• GET /health returns 503 if DB is unreachable
• Readiness includes memory usage threshold check
• Kubernetes manifests reference correct probes

File Map

• api/src/health/health.controller.ts — add /live and enhanced /health
• api/src/health/memory.health-indicator.ts — new
• api/src/health/health.module.ts — update providers

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Labels: observability, infrastructure
Priority: Medium | Difficulty: Beginner | Estimated Effort: 1d

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Labels: observability,infrastructure
Priority: Medium | Difficulty: Beginner | Estimated Effort: 1d
Backlog ID: REPO-035

[OlaGreat]

I'd like to take this on.

I'm a software engineer with experience in blockchain, backend systems, and open-source contribution. I've reviewed the issue and I'm confident I can deliver a clean implementation with tests covering the acceptance criteria. Happy to follow the project's existing conventions.

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #218)
2. Your PR will be reviewed by the XStreamRollz maintainers

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