Trace context not propagated - spans have different TraceIDs

[eliasecchig]

Summary

OpenTelemetry spans emitted by ADK have different TraceID values, preventing trace correlation in distributed tracing tools.

Observed Behavior

Each span (call_llm, execute_tool, HTTP POST) has a unique TraceID with no parent:

call_llm:        TraceID: 50ce4e4f...  Parent: 00000000...
execute_tool:    TraceID: 1ffc064e...  Parent: 00000000...
HTTP POST:       TraceID: b2df0a32...  Parent: 00000000...

Expected Behavior

Related spans should share the same TraceID and form a parent-child hierarchy.

Root Cause

In internal/telemetry/telemetry.go, the context from tracer.Start() is discarded:

_, span := tracer.Start(ctx, traceName)  // ctx discarded

Should be:

ctx, span := tracer.Start(ctx, traceName)  // propagate ctx

Workaround

Spans can be correlated via gcp.vertex.agent.invocation_id attribute, but standard trace views don't work.

Environment

• ADK v0.3.0
• Go 1.23
• OpenTelemetry SDK v1.39.0

[git-hulk]

@eliasecchig This should be related to #391, it requires passing the span context into the invocation/readonly/callback context.