feat(diagnostics-otel): Add trace context propagation and GenAI semantic conventions

Summary

This PR adds two related improvements to the diagnostics-otel plugin:

1. Trace context propagation — Diagnostic events now carry traceId and parentSpanId fields, enabling the OTel plugin to create proper parent-child span relationships instead of disconnected root spans.

2. GenAI semantic convention attributes — Model usage spans now include standardized gen_ai.* attributes alongside existing openclaw.* attributes, following the OTel GenAI semantic conventions.

Trace Hierarchy

Before (all root spans, unlinked):

openclaw.message.processed  (standalone)
openclaw.model.usage         (standalone)
openclaw.model.usage         (standalone)

After (linked parent-child traces):

openclaw.message.processed          ← parent span (traceId + spanId)
  └── chat claude-opus-4-6          ← child span (same traceId, parentSpanId = parent's spanId)
  └── chat claude-opus-4-6          ← child span (same traceId, parentSpanId = parent's spanId)

The trace context lifecycle:

1. logWebhookReceived generates a 32-hex-char traceId (UUID without dashes)
2. logMessageQueued stores the traceId on the session state when provided
3. logMessageProcessed reads the session's traceId, generates a 16-hex-char spanId, and emits both on the event
4. Model usage events inherit traceId and parentSpanId from the session state
5. The OTel plugin uses trace.setSpanContext() to create child spans under the proper parent

GenAI Convention Attributes Added

On model.usage spans (alongside existing openclaw.* attributes):

Span names updated for GenAI conventions:

• Model usage: chat ${model} (e.g., chat claude-opus-4-6)
• Message processed: unchanged (openclaw.message.processed)

Files Changed

Backwards Compatibility

• Fully backwards compatible: All trace context fields are optional (traceId?: string, parentSpanId?: string)
• No attributes removed: openclaw.* attributes remain on all spans — gen_ai.* attributes are added alongside
• No breaking changes to event types: DiagnosticEventInput omits ts and seq as before; the new fields are optional in the intersection types
• Span creation fallback: When no traceId is present, spans are created as root spans (existing behavior)
• The logMessageQueued function's traceId parameter is optional; existing callers don't need changes

How to Test

1. Unit tests:

   npx vitest run src/infra/diagnostic-events.test.ts
   npx vitest run extensions/diagnostics-otel/src/service.test.ts

2. Manual verification with a collector:

   • Configure diagnostics.otel.endpoint to point at a local OTLP collector or Jaeger
   • Send a message through any channel
   • Verify in the trace UI that openclaw.message.processed and chat <model> spans share the same traceId and have a parent-child relationship
   • Verify gen_ai.* attributes appear on model usage spans

3. Backwards compat check:

   • Run the full test suite to confirm no regressions
   • Verify openclaw.* attributes still appear on all spans

Greptile Summary

This PR adds trace context propagation and GenAI semantic convention attributes to the diagnostics-otel plugin. It introduces traceId/parentSpanId fields on diagnostic events, stores trace context on session state, and adds gen_ai.* attributes alongside existing openclaw.* attributes on model usage spans. Span names for model usage are updated to follow GenAI conventions (chat <model>).

• Trace context infrastructure: DiagnosticBaseEvent gains optional traceId and parentSpanId; SessionState gains traceId and currentSpanId. The OTel plugin's spanWithDuration now accepts parent context and uses trace.setSpanContext to establish parent-child links.
• GenAI semantic conventions: Model usage spans include gen_ai.operation.name, gen_ai.system, gen_ai.request.model, gen_ai.usage.input_tokens, and gen_ai.usage.output_tokens per the OTel GenAI spec.
• Trace hierarchy concern: logMessageProcessed emits its own generated spanId as parentSpanId, causing the OTel plugin to create a self-referential parent span rather than the intended root span. See inline comment for details.
• End-to-end wiring gap: No existing callers of logMessageQueued pass traceId, and model.usage emitters don't pass trace context, so the propagation chain is incomplete in practice. This may be intentional as groundwork for a follow-up PR.

Confidence Score: 3/5

• The PR is backwards-compatible and low-risk for regressions, but the trace hierarchy logic has a bug that will produce incorrect span relationships.
• The GenAI attribute additions and event type changes are clean and backwards-compatible. However, the trace context propagation has a logic issue where message.processed spans become self-referential instead of root spans, and the end-to-end wiring through callers is incomplete. These issues don't break existing functionality but mean the new trace linking feature won't produce the intended parent-child hierarchy.
• src/logging/diagnostic.ts — the parentSpanId emitted on message.processed events creates a self-referential span parent instead of the intended trace hierarchy.

_{Last reviewed commit: 52ad825}

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