What Does This Do

Fixes the test-agent trace decoders so spans sent with the v1.0 trace protocol keep their span events, and runs OpenTelemetrySmokeTest against every trace protocol.

• JSON decoder (MessageJson/SpanJson, used with the dd-apm-test-agent): reads the native span_events field as raw JSON and exposes it as the events meta tag. A new RawJsonAdapter copies the JSON value token by token into compact text, keeping number literals verbatim (no Double round-trip for nanosecond timestamps, decimals, or integers beyond long range).
• msgpack v1 decoder (SpanV1, used by in-process mock agents): decodes span events (field 12) instead of skipping them, into the same events tag the tracer writes for v0.4. Event names and attributes go through the string-table-aware helpers.
• OpenTelemetrySmokeTest: now a @ClassTemplate that runs once per ProtocolVersion (0.4, 0.5, 1.0), each run with its own app and test-agent backend.

Motivation

With v1.0, span events are no longer an events meta tag but a native span field, and neither decoder read it:

• The JSON decoder silently dropped span_events, so smoke assertions on the events tag failed under v1.0.
• SpanV1 skipped the field blindly. Besides losing the events, this consumed streaming strings without registering them, putting the string table out of sync. Later string indexes in the payload then resolved to the wrong strings or failed.

v0.4 is the default protocol, so nothing exercised the v1.0 path end to end. Running the smoke test per protocol covers it.

Additional Notes

• Test-only change: the decoder module and smoke tests are not part of the agent.
• I checked locally with debug logs that each smoke run negotiates its own endpoint: v0.4/traces, v0.5/traces, v1.0/traces.
• @ParameterizedClass cannot launch a separate app per protocol. With PER_CLASS it shares one instance across invocations, and class-level callbacks fire once per class template. So the smoke test uses a small ClassTemplateInvocationContextProvider that starts and stops each app in Before/AfterClassTemplateInvocationCallback.
• The smoke job runs three apps instead of one.
• Known difference: an empty span_events array decodes to "[]" in the JSON decoder but to no tag in SpanV1. TraceMapperV1 writes field 12 on every span, so SpanV1 cannot treat an empty array as meaningful.

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