diff --git a/crates/gateway/src/v1/iterate.rs b/crates/gateway/src/v1/iterate.rs
index 38e6538..06872d7 100644
--- a/crates/gateway/src/v1/iterate.rs
+++ b/crates/gateway/src/v1/iterate.rs
@@ -87,6 +87,14 @@ pub struct IterateResponse {
     pub validation: serde_json::Value,
     pub iterations: u32,
     pub history: Vec<IterateAttempt>,
+    /// Echoes the resolved trace id (caller-forwarded header, body
+    /// field, langfuse-middleware mint, or local fallback). Operators
+    /// pivot from this id straight into Langfuse + the
+    /// coordinator_sessions.jsonl join key. Cross-runtime parity with
+    /// Go's `validator.IterateResponse` (commit 6847bbc in
+    /// golangLAKEHOUSE).
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub trace_id: Option<String>,
 }
 
 #[derive(Serialize)]
@@ -94,6 +102,8 @@ pub struct IterateFailure {
     pub error: String,
     pub iterations: u32,
     pub history: Vec<IterateAttempt>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub trace_id: Option<String>,
 }
 
 pub async fn iterate(
@@ -217,6 +227,7 @@ pub async fn iterate(
                     validation: report,
                     iterations: iteration + 1,
                     history,
+                    trace_id: Some(trace_id.clone()),
                 })).into_response();
             }
             Err(err) => {
@@ -259,6 +270,7 @@ pub async fn iterate(
         error: format!("max iterations reached ({max_iter}) without passing validation"),
         iterations: max_iter,
         history,
+        trace_id: Some(trace_id.clone()),
     })).into_response()
 }
 
diff --git a/lakehouse.toml b/lakehouse.toml
index d0eea54..1c1582f 100644
--- a/lakehouse.toml
+++ b/lakehouse.toml
@@ -5,9 +5,13 @@ host = "0.0.0.0"
 port = 3100
 # Coordinator session JSONL — one row per /v1/iterate session for
 # offline DuckDB analysis. Cross-runtime parity with the Go-side
-# [validatord].session_log_path. Empty = disabled. Production:
-#   session_log_path = "/var/lib/lakehouse/gateway/sessions.jsonl"
-session_log_path = ""
+# [validatord].session_log_path. Set to the SAME path Go validatord
+# writes to so DuckDB queries see one unified longitudinal stream
+# across both runtimes (rows are tagged daemon="gateway" vs
+# daemon="validatord" so producers stay distinguishable). Append-write
+# is atomic at the row sizes both runtimes produce — both daemons
+# co-writing is safe.
+session_log_path = "/tmp/lakehouse-validator/sessions.jsonl"
 
 [storage]
 root = "./data"