fix(agents): preserve custom tracer provider with Cloud tracing

[dtran26]

Description

Preserves a caller-provided OpenTelemetry tracer provider when LiveKit Cloud tracing is enabled.

OpenTelemetry 2.x removed NodeTracerProvider.addSpanProcessor(). The previous fallback created a second provider and moved LiveKit's internal tracer to it, splitting application spans and LiveKit spans across different exporters.

Related to #1879.

Changes Made

• Add an optional registerSpanProcessor callback to setTracerProvider for providers backed by a mutable or delegating span processor.
• Retain addSpanProcessor() as the OpenTelemetry 1.x compatibility path.
• Preserve an incompatible custom provider and emit an actionable warning instead of silently replacing it.
• Add regression coverage for both the explicit registrar and no-registrar paths.
• Add a patch changeset for @livekit/agents.

Pre-Review Checklist

• Build passes: Package build, typecheck, lint, formatting, and focused tests pass locally
• AI-generated code reviewed: Removed implementation-specific assertions and unnecessary comments
• Changes explained: Root cause and compatibility behavior are documented above
• Scope appropriate: Only tracer-provider composition, its tests, and release note are changed
• Video demo: Not applicable; this is a telemetry-only change with automated regression coverage

Testing

• pnpm test agents/src/telemetry/traces.test.ts
• pnpm --filter @livekit/agents typecheck
• pnpm --filter @livekit/agents build
• pnpm -w format:write
• pnpm -w lint:fix
• Agent Playground smoke test not applicable; no agent media or session behavior changes

Additional Notes

pnpm --filter @livekit/agents api:check remains blocked on main by API Extractor's unsupported export * as syntax in dist/index.d.ts.

---

Note to reviewers: Please ensure the pre-review checklist is completed before starting your review.

[changeset-bot]

🦋 Changeset detected

Latest commit: e2c2f57

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 37 packages

Name	Type
@livekit/agents	Patch
@livekit/agents-plugin-anam	Patch
@livekit/agents-plugin-anthropic	Patch
@livekit/agents-plugin-assemblyai	Patch
@livekit/agents-plugin-azure	Patch
@livekit/agents-plugin-baseten	Patch
@livekit/agents-plugin-bey	Patch
@livekit/agents-plugin-cartesia	Patch
@livekit/agents-plugin-cerebras	Patch
@livekit/agents-plugin-deepgram	Patch
@livekit/agents-plugin-did	Patch
@livekit/agents-plugin-elevenlabs	Patch
@livekit/agents-plugin-fishaudio	Patch
@livekit/agents-plugin-google	Patch
@livekit/agents-plugin-hedra	Patch
@livekit/agents-plugin-hume	Patch
@livekit/agents-plugin-inworld	Patch
@livekit/agents-plugin-lemonslice	Patch
@livekit/agents-plugin-liveavatar	Patch
@livekit/agents-plugin-livekit	Patch
@livekit/agents-plugin-minimax	Patch
@livekit/agents-plugin-mistral	Patch
@livekit/agents-plugin-mistralai	Patch
@livekit/agents-plugin-neuphonic	Patch
@livekit/agents-plugin-openai	Patch
@livekit/agents-plugin-perplexity	Patch
@livekit/agents-plugin-phonic	Patch
@livekit/agents-plugin-resemble	Patch
@livekit/agents-plugin-rime	Patch
@livekit/agents-plugin-runway	Patch
@livekit/agents-plugin-sarvam	Patch
@livekit/agents-plugin-silero	Patch
@livekit/agents-plugin-soniox	Patch
@livekit/agents-plugin-tavus	Patch
@livekit/agents-plugins-test	Patch
@livekit/agents-plugin-trugen	Patch
@livekit/agents-plugin-xai	Patch

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[CLAassistant]

All committers have signed the CLA.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.