Add OpenTelemetry trace context propagation across Express middleware and Horizon listener in new src/observability/tracing.ts

[1nonlypiece]

📌 Description

The backend already emits Prometheus metrics and correlation IDs, but there is
no distributed tracing: a slow create_vault request that fans out into a
Soroban submission, an ETL enqueue, and a webhook delivery cannot be followed as
a single trace. Without spans it is hard to attribute latency in the Horizon →
event-processor → vault-store pipeline.

This issue wires OpenTelemetry tracing with W3C traceparent propagation across
the HTTP layer and into the background pipeline.

Goal: a single trace links an inbound request to its downstream Soroban,
job-queue, and webhook spans.

🎯 Requirements and Context

• src/observability/tracing.ts initializes a tracer with an OTLP exporter
  configured from env (OTEL_EXPORTER_OTLP_ENDPOINT), disabled when unset.
• An Express middleware extracts/injects traceparent and reuses the existing
  correlation ID as a span attribute.
• Spans are created around Soroban submission (soroban.ts), job handlers
  (jobs/handlers.ts), and webhook delivery.
• No-op tracer in test/dev so the suite runs without a collector.

🛠️ Suggested Execution

1. Create a branch

git checkout -b feature/otel-tracing

2. Implement changes

• Add src/observability/tracing.ts and a tracing middleware.
• Instrument the three downstream call sites with spans.
• Validate OTEL_* vars in src/config/env.ts.
• Document in docs/operations-metrics.md.

3. Test and commit

• Add src/tests/tracing.test.ts using an in-memory span exporter to assert
  parent/child linkage and correlation-ID attribute propagation.
• Run bun test src/tests/tracing.test.ts.

Example commit message

feat: OpenTelemetry trace propagation across HTTP and background pipeline

✅ Guidelines

• Minimum 95% test coverage on new/changed lines.
• No-op when no collector configured; document the env contract.
• Timeframe: 96 hours.

🏷️ Labels

type-feature · area-backend · type-enhancement · MAYBE REWARDED · GRANTFOX OSS · OFFICIAL CAMPAIGN

💬 Community & Support

• Join the Disciplr contributor Discord: https://discord.gg/xvNAvMJf
• Introduce yourself before starting to avoid duplicate work.

[YfengJ]

Hi maintainers, I would like to apply for this issue if it is available. If assigned, I would keep the implementation focused on trace propagation boundaries: config-gated OpenTelemetry initialization, Express traceparent extraction/injection, correlation ID span attributes, spans around Soroban/job/webhook paths, and tests with an in-memory exporter so local/dev remains no-op without a collector. I will wait for assignment or maintainer/GrantFox confirmation before opening a PR.

[aabxtract]

@aabxtract has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue, I’m a fullstack developer and I deliver ASAP

ℹ️ Repo Maintainers: To accept this application, review their application or assign @aabxtract to this issue.

[roobie001]

@roobie001 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello maintainer, can i work on this please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @roobie001 to this issue.

[grantfox-oss]

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

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #654)
2. Your PR will be reviewed by the Disciplr-Org maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

Congratulations, @aabxtract! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @aabxtract: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[YfengJ]

Thanks for the update. Since this issue is now assigned to @aabxtract, I will step back and will not compete on it.