diff --git a/runs/intervention-response-v2/prepare_pilot.py b/runs/intervention-response-v2/prepare_pilot.py
index 2b735d5..18f1b78 100644
--- a/runs/intervention-response-v2/prepare_pilot.py
+++ b/runs/intervention-response-v2/prepare_pilot.py
@@ -27,7 +27,7 @@ REPLAY_TIME_SCALE = 0.5
 EXPECTED_DURATION_S = 300.0
 SAFETY_DEADLINE_S = 360.0
 LOADS_REQ_S_GPU = {"low": 1.5, "mid": 2.125, "high": 3.125}
-REPLICATE_ROLES = ("high1", "high2", "high3")
+REPLICATE_ROLE_PAIRS = (("low1", "high1"), ("low2", "high2"), ("low3", "high3"))
 LOAD_ORDERS = {
     1: ("low", "mid", "high"),
     2: ("high", "low", "mid"),
@@ -103,12 +103,50 @@ def selection_record(selected: list[Any], *, duration_s: float) -> dict[str, Any
     }
 
 
-def materialize_study(source: Path, target: Path, *, replicate: int) -> Path:
+def resolve_role_trace(base: dict[str, Any], role: str) -> Path:
+    windows_path = Path(base["private"]["windows"])
+    windows = json.loads(windows_path.read_text(encoding="utf-8"))["windows"]
+    window_id = f"fidelity_pilot_{role}"
+    record = next(item for item in windows if item["window_id"] == window_id)
+    trace = Path(record["trace_file"])
+    if not trace.is_absolute():
+        trace = (windows_path.parent / trace).resolve()
+    return trace
+
+
+def merge_role_traces(sources: tuple[Path, Path], target: Path) -> dict[str, Any]:
+    target.parent.mkdir(parents=True, exist_ok=True)
+    temporary = target.with_suffix(target.suffix + ".tmp")
+    rows = 0
+    with temporary.open("w", encoding="utf-8") as output:
+        for source in sources:
+            with source.open(encoding="utf-8") as input_file:
+                for line in input_file:
+                    if not line.strip():
+                        continue
+                    json.loads(line)
+                    output.write(line if line.endswith("\n") else line + "\n")
+                    rows += 1
+    os.replace(temporary, target)
+    return {
+        "path": str(target),
+        "sha256": sha256_file(target),
+        "bytes": target.stat().st_size,
+        "rows": rows,
+        "sources": [str(source) for source in sources],
+        "source_sha256": [sha256_file(source) for source in sources],
+    }
+
+
+def materialize_study(
+    source: Path, target: Path, *, replicate: int, trace_override: Path
+) -> Path:
     payload = json.loads(source.read_text(encoding="utf-8"))
     payload["study_id"] = f"phase-aware-telemetry-v2-rep{replicate}"
     payload["hardware"]["host_candidates"] = ["dash0"]
     payload["engine"]["engine_version"] = "0.24.1.dev3+opprof"
     trace = payload["trace"]
+    trace["trace_file_override"] = str(trace_override)
     trace["replay_time_scale"] = REPLAY_TIME_SCALE
     trace["early_stop_max_lag_s"] = None
     trace["early_stop_max_elapsed_s"] = SAFETY_DEADLINE_S
@@ -128,10 +166,21 @@ def build_manifest(
     repetitions = {}
     selection_hashes = []
     selected_ids_by_replicate: dict[int, set[str]] = {}
-    for replicate, role in enumerate(REPLICATE_ROLES, start=1):
-        source_study = Path(base["private"]["studies"][role]["tp4"])
+    merged_traces = {}
+    for replicate, roles in enumerate(REPLICATE_ROLE_PAIRS, start=1):
+        source_study = Path(base["private"]["studies"][roles[1]]["tp4"])
+        source_traces = tuple(resolve_role_trace(base, role) for role in roles)
+        merged_trace = private_root / "traces" / f"rep{replicate}.jsonl"
+        merged_traces[str(replicate)] = merge_role_traces(
+            source_traces, merged_trace
+        )
         target_study = private_root / "studies" / f"rep{replicate}-tp4.json"
-        materialize_study(source_study, target_study, replicate=replicate)
+        materialize_study(
+            source_study,
+            target_study,
+            replicate=replicate,
+            trace_override=merged_trace,
+        )
         study = load_study_spec(target_study)
         window, requests = load_trace_requests(study, study_spec_path=target_study)
         duration_s = float(window.window_end - window.window_start)
@@ -159,7 +208,8 @@ def build_manifest(
             selection_hashes.append(record["request_id_order_sha256"])
         selected_ids_by_replicate[replicate] = selected_ids_by_level["high"]
         repetitions[str(replicate)] = {
-            "source_role": role,
+            "source_roles": list(roles),
+            "merged_trace": merged_traces[str(replicate)],
             "study": str(target_study),
             "study_sha256": sha256_file(target_study),
             "duration_s": duration_s,
@@ -219,6 +269,7 @@ def build_manifest(
             "disable_slo_early_stop": True,
         },
         "burnin": burnin,
+        "private": {"merged_traces": merged_traces},
         "repetitions": repetitions,
         "sessions": sessions,
         "checkpoints": {