feat: forward LD context keys to errors, logs, and custom spans

[Vadman97]

Summary

• Spread _ldContextKeys (set via LDObserve.setLDContextKeyAttributes) into all OTel data types where it makes semantic sense, not just metrics.
• startSpan wrapper now applies contextKeys to every span before invoking the caller, so user-created custom spans inherit pathTemplate / owner / account / route attributes automatically. Caller setAttributes calls win on key collisions (OTel merges with last-write-wins).
• _recordLog spreads contextKeys into the addEvent('log', …) payload so log events carry the same dimensions as their containing span.
• _recordErrorMessage no longer needs an explicit spread because the startSpan wrapper handles it; comment added at the call site.

Why

Previously _ldContextKeys only flowed into recordCount / recordGauge / recordHistogram / recordUpDownCounter (#510 / commit e49d4812f), so error, log, and custom-span queries could not group by team or route. This meant LD Observability dashboards couldn't replicate Datadog RUM's per-team and per-route error and log breakdowns. After this change, queries like errors group_by context.contextKeys.pathTemplate and logs group_by context.contextKeys.owner produce real values, closing the last big gap relative to the Datadog frontend-errors dashboard.

Coverage matrix

Data type	Before	After
Counter / Gauge / Histogram / UpDownCounter metric	✅	✅
Click / page-view / user-interaction spans	✅	✅
Errors (recordError / _recordErrorMessage)	❌	✅ (via startSpan wrapper)
Logs (_recordLog addEvent)	❌	✅
Custom spans created via startSpan	❌	✅

Test plan

• yarn vitest run src/__tests__/sdk.test.ts — 14/14 passing locally
  • new tests cover: error span attrs, log addEvent attrs, custom span attrs, override semantics, no-context-keys no-op
• yarn turbo run build --filter '@launchdarkly/observability' — clean build
• yarn format-check — passes
• Verify in catfood: queries on errors / logs grouped by context.contextKeys.pathTemplate / owner / accountId populate after a gonfalon SDK bump

🤖 Generated with Claude Code

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Note

Medium Risk
Touches core tracing/logging/error instrumentation by injecting _ldContextKeys into startSpan and log events, which could change span attributes and override behavior across all spans.

Overview
LD context keys set via setLDContextKeyAttributes are now forwarded beyond metrics: startSpan injects them onto every created span (including user custom spans), and _recordLog includes them in addEvent('log', ...) attributes.

Error recording relies on the startSpan wrapper for context key attachment (instead of explicitly spreading them in _recordErrorMessage), and new Vitest coverage asserts propagation plus last-write-wins override semantics and the no-context-keys no-op case.

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