diff --git a/cmd/validatord/main.go b/cmd/validatord/main.go
index 6179a9c..a4264ba 100644
--- a/cmd/validatord/main.go
+++ b/cmd/validatord/main.go
@@ -244,15 +244,23 @@ func (h *handlers) handleIterate(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Pull the per-request trace id from the langfuse middleware. If
-	// the caller forwarded an upstream trace via X-Lakehouse-Trace-Id
-	// the middleware reuses that one; otherwise it minted a fresh trace
-	// at HTTP entry. When Langfuse isn't configured at all the
-	// middleware skips the mint, so we generate a fallback id locally —
-	// session_id MUST always be populated so the JSONL log + Langfuse
-	// (when later configured) can correlate by id across logs.
-	// Surfaced 2026-05-02 deploy: empty session_id breaks DuckDB
-	// joins on coordinator_sessions.jsonl ↔ replay_runs.jsonl.
+	// Resolve the parent trace id, in priority order:
+	//   1. req.TraceID (caller put it in the JSON body)
+	//   2. X-Lakehouse-Trace-Id header (read DIRECTLY here so the path
+	//      works even when Langfuse is off and the middleware is a
+	//      passthrough — matches Rust's iterate handler shape)
+	//   3. context value set by the langfuse middleware (when Langfuse
+	//      is configured)
+	//   4. fallback to a locally-minted time-ordered hex id
+	//
+	// Surfaced 2026-05-02 cross-runtime test: Go was minting fallback
+	// even when caller forwarded the header, because middleware
+	// passthrough mode never read it. Reading the header here closes
+	// the gap and makes Go behavior match Rust regardless of
+	// Langfuse configuration.
+	if req.TraceID == "" {
+		req.TraceID = r.Header.Get(shared.TraceIDHeader)
+	}
 	if req.TraceID == "" {
 		req.TraceID = shared.TraceIDFromCtx(r.Context())
 	}