feat(go): report source context for recorded errors

[abelonogov-ld]

Summary

Go errors arrived in the errors UI as a bare text stacktrace with no source, and the frames on top belonged to the SDK rather than to the application, so the first thing you saw was span.RecordError. This does for Go what #693 did for Python.

• RecordError now attaches exception.structured_stacktrace: function name, file, line and a window of source lines around each frame, read from the running host. Ingestion prefers this attribute over the text stacktrace.
• Frames belonging to this SDK and to the OTel API are trimmed, so the first reported frame is the caller's own code.
• When an error wraps another, the stack from the innermost error is reported instead of the one captured at the wrap point. pkg/errors.Wrap records a fresh stack where the wrapping happened, which meant the frames pointed at the handler that added context rather than at where the error came from. This applies to the text stacktrace too, not just the structured one.
• e2e/go-plugin gained four routes that record a plain error, one with a stack, a wrapped one, and one raised from a closure inside a goroutine, plus README instructions for pointing the example at a backend running on localhost.

The text stacktrace remains the fallback for errors recorded outside this path; the parsing of those on the backend is fixed separately in launchdarkly/observability#1596.

Test plan

• go test ./... in go/. Unit tests cover picking the innermost stack through both pkg/errors and standard wrapping, source windows clipped at the start and end of a file, a missing file, a line past the end of a file, long-line truncation, and function-name shortening.
• stacktrace_record_test.go drives a real RecordError from an external test package through an in-memory exporter and asserts the first frame is the caller, which is what proves the trimming works from outside the module.
• Ran the e2e example against a local backend and hit all four routes: frames start in app code, closures and goroutine frames are named, and source context is present.

Made with Cursor

[Vadman97]

long needed; let's get this deployed to our observability / gonfalon services to try out!

[cursor]

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