Add Langfuse as an OTel trace transport for MCP request lifecycle tracking.
Changes:
- New src/lib/langfuse-transport.ts: initializes LangfuseSpanProcessor when
ASK262_LANGFUSE_ENABLED=true with valid credentials
- src/lib/tracing.ts: add metadata to TraceContext, propagate it to child spans,
use startActiveSpan for proper OTel context, add setupTracing() entry point,
add getSessionMetadata() for version/transport metadata
- src/lib/logger.ts: include TraceContext.metadata in JSON log mixin
- src/mcp-server-{http,stdio}.ts: call setupTracing() at startup, pass
version/transport metadata through withSpan/withSpanContext
- src/lib/fireworks-embeddings.ts: wrap API calls in withSpan() with gen_ai
attributes for Langfuse generation/cost tracking
- .env.example: add LANGFUSE_* configuration variables
- AGENTS.md: document Langfuse integration
- package.json: add @langfuse/tracing, @langfuse/otel, @opentelemetry/sdk-node
bendtherules