feat(nats): add OTel span instrumentation

[bramwelt]

Summary

• Adds natsHeaderCarrier type implementing propagation.TextMapCarrier for NATS header-based trace context propagation
• Wraps Request() with a SpanKindClient span that injects trace context into outbound NATS message headers
• Changes QueueSubscribe() handler signature to func(ctx context.Context, msg *nats.Msg) and adds SpanKindConsumer span that extracts trace context from inbound message headers; updates all 3 call sites in subscriptions.go
• Wraps ForwardEmail and JWT JWKS HTTP clients with otelhttp.NewTransport for outbound HTTP tracing

Issue: LFXV2-1743

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds OpenTelemetry tracing instrumentation around the service’s NATS messaging and key outbound HTTP clients, enabling end-to-end trace context propagation across NATS headers and HTTP requests.

Changes:

• Introduces a natsHeaderCarrier to inject/extract trace context via NATS message headers.
• Instruments NATS Request() (client span + context injection) and QueueSubscribe() handlers (consumer span + context extraction), updating subscription call sites accordingly.
• Wraps ForwardEmail and Auth0 JWKS HTTP clients with otelhttp.NewTransport and updates OTel-related dependencies.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/infrastructure/nats/tracing.go	Adds natsHeaderCarrier and package tracer used for NATS trace propagation.
internal/infrastructure/nats/tracing_test.go	Adds unit tests for the NATS header carrier behavior.
internal/infrastructure/nats/client.go	Wraps NATS request/consume flows with spans and injects/extracts context from headers.
internal/infrastructure/jwt/parser.go	Instruments JWKS HTTP client transport with otelhttp.
internal/infrastructure/forwardemail/client.go	Instruments ForwardEmail HTTP client transport with otelhttp.
cmd/forwards-api/service/subscriptions.go	Updates NATS queue subscription handlers to accept a propagated context.Context.
go.mod	Adds otelhttp/testify and bumps OTel core modules; introduces mixed OTel minor versions.
go.sum	Records checksums for newly added/updated dependencies.

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[bramwelt]

Review Feedback Addressed

Commit: 1fcd6d3

Changes Made

• internal/infrastructure/nats/tracing.go: Added nil guard to natsHeaderCarrier.Set() to prevent panic on nil map assignment (per copilot-pull-request-reviewer)

No Change Needed

• go.mod: OTel version mix between core SDK and contrib modules — intentional, different Go modules with independent release cadences (flagged by copilot-pull-request-reviewer)
• go.mod (×4): BSD-3-Clause + Google patent license — standard transitive deps from OpenTelemetry SDK, does not affect LFX MIT-licensed code (flagged by github-license-compliance)

Threads Resolved

5 of 5 unresolved threads addressed.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 10 changed files in this pull request and generated 1 comment.

[bramwelt]

Review Feedback Addressed (Round 2)

No Change Needed

• internal/infrastructure/observability/otel.go: autoexport handles OTEL_METRICS_EXPORTER=none and OTEL_LOGS_EXPORTER=none with no-op implementations — no unexpected connections or startup failures. Exporters not explicitly set in the Helm chart will use the autoexport default ("otlp"), which is correct for a production service. (flagged by copilot-pull-request-reviewer)

Threads Resolved

1 of 1 unresolved threads addressed.