fix(cloud): propagate OTEL trace context across worker→DO boundary#320
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RhysSullivan merged 1 commit intomainfrom Apr 18, 2026
Merged
fix(cloud): propagate OTEL trace context across worker→DO boundary#320RhysSullivan merged 1 commit intomainfrom
RhysSullivan merged 1 commit intomainfrom
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Worker and McpSessionDO run in separate isolates with independent WebSdk tracer providers, so nothing carried trace context across stub.init() / stub.handleRequest() — the DO emitted a brand-new root trace per request and mcp.request + McpSessionDO.* never stitched in Axiom. Ferry the worker-side span's SpanContext across as a W3C traceparent: - mcp.ts builds it from Effect.currentSpan and either injects a traceparent header on the forwarded Request (handleRequest) or passes it as a new second arg to stub.init(token, traceparent). - mcp-session.ts parses it and uses OtelTracer.withSpanContext so the DO's root Effect span lands under the worker span. Regression guard added to the miniflare e2e suite (extended CapturedSpan to track traceId/spanId/parentSpanId) — asserts McpSessionDO.init shares trace_id with mcp.request and has its spanId as parent_span_id, plus the same for a follow-up tools/list → McpSessionDO.handleRequest.
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Summary
mcp.request(worker) andMcpSessionDO.*(DO) in separate traces — the worker's WebSdk and the DO's WebSdk live in different isolates and nothing carried OTEL context across thestub.init()/stub.handleRequest()RPC, so the DO emitted a brand-new root trace per call.traceparentfromEffect.currentSpanand ferries it to the DO (header onhandleRequest, second arg oninit). DO parses it and anchors its root span viaOtelTracer.withSpanContext.McpSessionDO.init/handleRequestmust sharetrace_idwith the correspondingmcp.requestand point to it viaparent_span_id.Test plan
bun run vitest run --config vitest.node.config.ts(cloud): 29/29 pass, including the new propagation assertion.mcp.request+McpSessionDO.*into a single trace.