feat: add OTel spans to NATS request operations

[bramwelt]

Summary

• Adds OpenTelemetry client spans around NATS RequestMsg calls so NATS request-reply operations are visible in Datadog APM traces
• Injects W3C trace context into NATS message headers for cross-service propagation to fga-sync
• Uses semconv/v1.39.0 constants for all standard messaging attributes; defines a local const for messaging.message.reply.body.size (no semconv equivalent yet)
• Respects ctx deadline — uses the shorter of the explicit timeout and ctx.Deadline(); short-circuits with context.DeadlineExceeded if the deadline is already past
• Adds TestMessagingRepository_Request_CreatesSpan to verify span creation and attributes via in-memory exporter

Changes

• internal/infrastructure/messaging/messaging_repository.go — span instrumentation, natsHeaderCarrier, ctx-deadline timeout handling
• internal/infrastructure/messaging/messaging_repository_test.go — span creation test with provider save/restore
• go.mod — promote otel/trace from indirect to direct dependency

Issue: LFXV2-1743

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Walkthrough

This PR integrates OpenTelemetry tracing into NATS messaging by promoting the otel/trace dependency to direct, instrumenting the messaging repository's Request method with span creation and context propagation, and validating span attributes through unit tests.

Changes

OpenTelemetry tracing for NATS messaging

Layer / File(s)	Summary
OTel dependency and package-level instrumentation go.mod, internal/infrastructure/messaging/messaging_repository.go	go.opentelemetry.io/otel/trace v1.40.0 is promoted from indirect to direct dependency. Package-level tracer, reply size attribute key, and natsHeaderCarrier adapter for trace context injection/extraction are initialized.
Request method span creation and context propagation internal/infrastructure/messaging/messaging_repository.go	Request method creates a client span, injects trace context into NATS message headers, manages timeout by short-circuiting to the earlier of explicit timeout and context deadline, sends via RequestMsg, records reply body size attribute, and sets span status on success or records error status on failure.
Span creation and attribute validation tests internal/infrastructure/messaging/messaging_repository_test.go	OTel test imports (sdktrace, tracetest, semconv) are added. New test TestMessagingRepository_Request_CreatesSpan uses an in-memory span exporter to verify the Request method produces a span named "nats.request" with messaging system and destination name attributes.

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat: add OTel spans to NATS request operations' clearly summarizes the main change: adding OpenTelemetry spans to NATS request operations.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description accurately describes the changeset, detailing OpenTelemetry instrumentation additions to NATS messaging, trace context injection, semantic conventions usage, context deadline handling, and test additions.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch tbramwell/LFXV2-1743-nats-span-instrumentation

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[Copilot]

Pull request overview

This PR instruments the NATS request/reply path in the messaging repository with OpenTelemetry client spans and injects W3C trace context into NATS message headers to enable cross-service trace propagation (e.g., into fga-sync).

Changes:

• Added an OTel client span around NATS request operations, including standard messaging semantic convention attributes and reply body size.
• Injected the current trace context into outbound NATS message headers via a TextMapCarrier adapter.
• Added a unit test using an in-memory trace exporter to verify span creation/attributes; updated go.mod to make otel/trace a direct dependency.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
internal/infrastructure/messaging/messaging_repository.go	Adds OTel span instrumentation, context-propagation injection, and ctx deadline/timeout handling for NATS requests.
internal/infrastructure/messaging/messaging_repository_test.go	Adds a unit test verifying that Request creates a nats.request span with expected attributes.
go.mod	Promotes go.opentelemetry.io/otel/trace from indirect to direct dependency.

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[bramwelt]

Review Feedback Addressed

Commit: f6b2f82

Changes Made

• messaging_repository.go:120-132: Flattened the ctx-deadline/timeout guard so that a caller-supplied timeout <= 0 is also caught. The previous nested structure meant remaining < timeout was false when timeout was negative and remaining was positive, silently passing an invalid duration to RequestMsg. Now the ctx deadline is clamped unconditionally (when shorter), followed by a single timeout <= 0 short-circuit with context.DeadlineExceeded. (per copilot-pull-request-reviewer[bot])

Threads Resolved

1 of 1 unresolved threads addressed.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[bramwelt]

Review Feedback Addressed

Commit: 3eb55c0

Changes Made

• messaging_repository.go:140: Replaced err.Error() with constants.ErrMsgNATSRequestFailed as the span status description. Raw NATS error strings are high-cardinality and can leak internal server addresses/port details into traces. RecordError(err) already captures the full error on the span event — the status description should be a stable, low-cardinality string. (per copilot-pull-request-reviewer[bot])

Threads Resolved

1 of 1 unresolved threads addressed in this iteration.