diff --git a/docs/adr/ADR-355-local-empty-room-bootstrap-prior.md b/docs/adr/ADR-355-local-empty-room-bootstrap-prior.md
index 5eb4ba732..1ec6ee36d 100644
--- a/docs/adr/ADR-355-local-empty-room-bootstrap-prior.md
+++ b/docs/adr/ADR-355-local-empty-room-bootstrap-prior.md
@@ -25,8 +25,10 @@ prior only after two server controlled stages:
 
 1. Normal calibration reaches both 1,000 accepted frames and 600 seconds.
    The frame target represents twenty complete fifty frame runtime windows.
-   Collection binds to the first accepted ESP32 source and rejects frames from
-   other radios for that single link model.
+   A caller may select one currently live ESP32 source. The server checks its
+   freshness before replacing an active bootstrap prior, binds collection to
+   that source, and rejects frames from other radios. When no source is
+   selected, the first accepted ESP32 source preserves legacy behavior.
 2. Promotion observes 12 new samples spaced by at least one second. Each
    sample has a four second bounded acquisition timeout. At least 10 must
    resolve empty, all ticks must be fresh, and none may publish numeric vital
@@ -89,6 +91,9 @@ occupied sequences. Empty data is never relabeled as human training.
    gate as `sensing_update`. When the bootstrap background matches, it emits
    absent state, zero people, null numeric rates, and an explicit abstention
    reason instead of forwarding raw edge candidates.
+7. `POST /api/v1/calibration/start?source_node_id=N` selects a live source for
+   deterministic single link capture. A missing or stale selection fails
+   without disabling the active bootstrap prior.
 
 ## Measured installation evidence
 
@@ -111,3 +116,5 @@ and data directory. Status must report `binding_mode=bootstrap_only`, zero
 collection frames, and false authority for calibrated evidence and numeric
 vitals. Twelve fresh empty samples must contain no numeric vital signs.
 Starting a new room calibration must replace the prior and begin at frame zero.
+When several radios are live, selecting Node 5 must leave Nodes 3 and 7 out of
+the source set for the entire capture.
diff --git a/v2/crates/wifi-densepose-sensing-server/src/main.rs b/v2/crates/wifi-densepose-sensing-server/src/main.rs
index 0c0628301..16261c1a1 100644
--- a/v2/crates/wifi-densepose-sensing-server/src/main.rs
+++ b/v2/crates/wifi-densepose-sensing-server/src/main.rs
@@ -6159,6 +6159,14 @@ mod bootstrap_vital_publication_tests {
         assert!(!calibration_source_accepts(&sources, 3));
     }
 
+    #[test]
+    fn explicit_single_link_source_rejects_other_live_nodes() {
+        let sources = std::collections::BTreeSet::from([5]);
+        assert!(calibration_source_accepts(&sources, 5));
+        assert!(!calibration_source_accepts(&sources, 3));
+        assert!(!calibration_source_accepts(&sources, 7));
+    }
+
     fn strong_candidates() -> VitalSigns {
         VitalSigns {
             breathing_rate_bpm: Some(15.0),
@@ -6249,8 +6257,33 @@ mod bootstrap_vital_publication_tests {
 
 // ── Field model calibration endpoints (eigenvalue person counting) ──────────
 
-async fn calibration_start(State(state): State<SharedState>) -> Json<serde_json::Value> {
+#[derive(Debug, Default, Deserialize)]
+struct CalibrationStartQuery {
+    /// Optional explicit single-link source. When omitted, the first accepted
+    /// ESP32 packet preserves the legacy binding behavior.
+    source_node_id: Option<u8>,
+}
+
+async fn calibration_start(
+    State(state): State<SharedState>,
+    Query(query): Query<CalibrationStartQuery>,
+) -> Json<serde_json::Value> {
     let mut s = state.write().await;
+    if let Some(source_node_id) = query.source_node_id {
+        let now = std::time::Instant::now();
+        let source_is_live = s.node_states.get(&source_node_id).is_some_and(|node| {
+            node.last_frame_time
+                .is_some_and(|seen| now.saturating_duration_since(seen) < ESP32_OFFLINE_TIMEOUT)
+        });
+        if !source_is_live {
+            return Json(serde_json::json!({
+                "success": false,
+                "error_code": "calibration_source_unavailable",
+                "error": "The requested calibration source is missing or stale.",
+                "source_node_id": source_node_id,
+            }));
+        }
+    }
     if s.bootstrap_baseline_active {
         s.field_model = None;
         s.bootstrap_baseline_active = false;
@@ -6279,10 +6312,14 @@ async fn calibration_start(State(state): State<SharedState>) -> Json<serde_json:
             s.field_model = Some(fm);
             s.calibration_model_id = Some(opaque_calibration_model_id());
             s.calibration_source_node_ids.clear();
+            if let Some(source_node_id) = query.source_node_id {
+                s.calibration_source_node_ids.insert(source_node_id);
+            }
             Json(serde_json::json!({
                 "success": true,
                 "message": "Calibration started — keep room empty while frames accumulate.",
                 "model_id": s.calibration_model_id,
+                "source_node_ids": s.calibration_source_node_ids,
             }))
         }
         // ADR-080 #2: FieldModel init error chain stays server-side only.