diff --git a/justfile b/justfile
index 17d6229..4f2c7ab 100644
--- a/justfile
+++ b/justfile
@@ -212,6 +212,10 @@ probe-projected-replay steps="20":
 probe-uat:
     uv run python -m projected_grpo.probe_uat
 
+# Trajectory comparator for the warmup-gen runs (vanilla vs projected).
+probe-traj:
+    uv run python -m projected_grpo.probe_traj
+
 # Phase 2 pilot analyzer: reads out/train_pilot_*.safetensors, prints trajectories
 # and per-arm aggregates, applies decision rules from spec2.md.
 phase2-analyze pattern="_pilot_*":
diff --git a/src/projected_grpo/probe_traj.py b/src/projected_grpo/probe_traj.py
new file mode 100644
index 0000000..bc853b1
--- /dev/null
+++ b/src/projected_grpo/probe_traj.py
@@ -0,0 +1,113 @@
+"""Per-step trajectory printer for the warmup->gen runs.
+
+Reads out/probe_distill/{tag}/step_*.jsonl.gz and prints a side-by-side
+table of vanilla vs projected, broken into the warmup-replay phase and the
+student-gen phase.
+"""
+from __future__ import annotations
+
+import gzip
+import json
+import sys
+from pathlib import Path
+
+
+def load_run(run_dir: Path) -> list[dict]:
+    rows = []
+    for path in sorted(run_dir.glob("step_*.jsonl.gz")):
+        with gzip.open(path, "rt") as f:
+            for line in f:
+                rows.append(json.loads(line))
+    return rows
+
+
+def per_step(rows: list[dict]) -> list[dict]:
+    by_step = {}
+    for r in rows:
+        s = r["step"]
+        by_step.setdefault(s, []).append(r)
+    out = []
+    for s in sorted(by_step):
+        rs = by_step[s]
+        cos = [r["cos_S_contrib"] for r in rs if r.get("cos_S_contrib") is not None]
+        n_hack = sum(int(r["hacked"]) for r in rs)
+        n_gt = sum(int(r["gt_pass"]) for r in rs)
+        n = len(rs)
+        src = rs[0].get("src_pool", "?")
+        out.append({
+            "step": s,
+            "n": n,
+            "src": src,
+            "hack": f"{n_hack}/{n}",
+            "gt": f"{n_gt}/{n}",
+            "cos_mean": sum(cos)/len(cos) if cos else float("nan"),
+            "cos_in": rs[0].get("mean_cos_in", float("nan")),
+            "cos_out": rs[0].get("mean_cos_out", float("nan")),
+            "fired": rs[0].get("frac_fired", float("nan")),
+        })
+    return out
+
+
+def main(tag_v: str = "warmupgen_vanilla_seed41", tag_p: str = "warmupgen_projected_svd_seed41"):
+    root = Path("out/probe_distill")
+    v = per_step(load_run(root / tag_v))
+    p = per_step(load_run(root / tag_p))
+
+    print(f"\n{'='*120}")
+    print(f"Warmup -> student-gen comparison (vanilla vs projected SVD)")
+    print(f"{'='*120}")
+    print(f"{'step':>4} {'src':>14}   "
+          f"{'V.hack':>8} {'V.gt':>6} {'V.cos':>7} {'V.cin':>7} {'V.cout':>7} {'V.fired':>7}   "
+          f"{'P.hack':>8} {'P.gt':>6} {'P.cos':>7} {'P.cin':>7} {'P.cout':>7} {'P.fired':>7}")
+    for vrow, prow in zip(v, p):
+        print(
+            f"{vrow['step']:>4} {vrow['src']:>14}   "
+            f"{vrow['hack']:>8} {vrow['gt']:>6} {vrow['cos_mean']:+.3f}  {vrow['cos_in']:+.3f}  {vrow['cos_out']:+.3f}  {vrow['fired']:.2f}    "
+            f"{prow['hack']:>8} {prow['gt']:>6} {prow['cos_mean']:+.3f}  {prow['cos_in']:+.3f}  {prow['cos_out']:+.3f}  {prow['fired']:.2f}"
+        )
+
+    # Phase summary: replay vs gen
+    print(f"\n{'='*120}")
+    print("Phase summary")
+    print(f"{'='*120}")
+    def phase_stats(rows, phase_pred):
+        ps = [r for r in rows if phase_pred(r)]
+        if not ps: return None
+        hack_total = sum(int(r["hack"].split("/")[0]) for r in ps)
+        n_total = sum(int(r["hack"].split("/")[1]) for r in ps)
+        gt_total = sum(int(r["gt"].split("/")[0]) for r in ps)
+        cins = [r["cos_in"] for r in ps if isinstance(r["cos_in"], (int,float))]
+        return {
+            "n_steps": len(ps),
+            "hack_rate": hack_total/max(1,n_total),
+            "gt_rate": gt_total/max(1,n_total),
+            "cin_mean": sum(cins)/max(1,len(cins)) if cins else float("nan"),
+        }
+
+    is_replay = lambda r: "teacher_pool" in r["src"] or "base_pool" in r["src"]
+    is_gen    = lambda r: r["src"] == "student_gen" or r["src"] is None
+
+    for label, rows in [("vanilla", v), ("projected", p)]:
+        rep = phase_stats(rows, is_replay)
+        gen = phase_stats(rows, is_gen)
+        print(f"\n{label}:")
+        if rep:
+            print(f"  warmup replay (n_steps={rep['n_steps']:2d}): hack_rate={rep['hack_rate']:.3f}  gt_rate={rep['gt_rate']:.3f}  cos_in_mean={rep['cin_mean']:+.4f}")
+        if gen:
+            print(f"  student gen   (n_steps={gen['n_steps']:2d}): hack_rate={gen['hack_rate']:.3f}  gt_rate={gen['gt_rate']:.3f}  cos_in_mean={gen['cin_mean']:+.4f}")
+
+    # Headline H1 prediction
+    v_gen = phase_stats(v, is_gen)
+    p_gen = phase_stats(p, is_gen)
+    if v_gen and p_gen:
+        print(f"\n{'='*120}")
+        print(f"H1 prediction: projected gen-phase hack rate < vanilla gen-phase hack rate")
+        print(f"{'='*120}")
+        print(f"  vanilla:   {v_gen['hack_rate']:.3f}")
+        print(f"  projected: {p_gen['hack_rate']:.3f}")
+        delta = v_gen['hack_rate'] - p_gen['hack_rate']
+        print(f"  delta:     {delta:+.3f}  ({'PASS' if delta > 0 else 'FAIL or null'})")
+
+
+if __name__ == "__main__":
+    main(*(sys.argv[1:3] if len(sys.argv) >= 3 else ()))