feat(opencode): bridge global OTel tracer for AI SDK telemetry

[kitlangton]

Summary

• Adds a lightweight BasicTracerProvider bridge (src/otel-bridge.ts) that registers a global OTel tracer when OTEL_EXPORTER_OTLP_ENDPOINT is set
• Enables AI SDK's experimental_telemetry spans to be exported alongside Effect's own OTLP spans (added in feat(opencode): add OTLP observability support #21387)
• Turns on recordInputs/recordOutputs on both streamText (llm.ts) and generateObject (agent.ts) call sites so full prompt/response content is captured as span attributes
• Telemetry auto-enables when the OTLP endpoint env var is set — no separate config flag needed
• Zero runtime cost when OTEL_EXPORTER_OTLP_ENDPOINT is unset (dynamic imports, conditional init)

How it works

Effect's Otlp.layerJson instruments Effect services but uses an internal fiber-scoped tracer — it does NOT register a global TracerProvider. The AI SDK's experimental_telemetry reads from @opentelemetry/api's global tracer, so without a global provider its spans are silently dropped.

This bridge fills the gap with BasicTracerProvider from @opentelemetry/sdk-trace-base (much lighter than @opentelemetry/sdk-node) exporting via OTLPTraceExporter (HTTP/JSON) to the same endpoint. Both trace streams land in the same collector.

What you get

With OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 opencode:

• Effect spans: Session.create, Tool.run, Provider.chat, etc.
• AI SDK spans: ai.streamText, ai.streamText.doStream, ai.toolCall
• Message content (via recordInputs/recordOutputs): ai.prompt, ai.response.text, ai.toolCall.args, ai.toolCall.result, ai.usage.*
• Metadata: ai.telemetry.metadata.userId, ai.telemetry.metadata.sessionId

Works with any OTLP/HTTP collector — Jaeger, Aspire, SigNoz, Grafana Tempo, or a local dev tool like leto.

New deps

• @opentelemetry/sdk-trace-base — BasicTracerProvider + BatchSpanProcessor
• @opentelemetry/exporter-trace-otlp-http — OTLP/HTTP JSON exporter
• @opentelemetry/api — global tracer registration
• @opentelemetry/resources + @opentelemetry/semantic-conventions — service resource attributes

Related

• feat(opencode): add OTLP observability support #21387 — Effect OTLP layer (already merged, complements this)
• feat(telemetry): add OpenTelemetry instrumentation with Aspire Dashboard support #6629 — Luke's comprehensive Aspire integration (draft, much broader scope — this PR is the minimal bridge)
• add experimental.open_telemetry config option to enable OTEL spans #4978, feat(telemetry): Add userId and sessionId metadata to experimental_telemetry #5279, fix(telemetry): restore userId and sessionId metadata in experimental_telemetry #8195 — original experimental_telemetry work

Test plan

• Set OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318, run Jaeger/Aspire/leto, verify AI SDK spans appear with message content
• Verify Effect spans still export correctly
• Verify zero overhead when env var is unset (no OTel packages loaded)
• bun run typecheck passes across all 13 packages