trajectory map = scatter not polyline (scales to 10 rounds); persist base event; offline plot_run.py

The pareto map drew a base->r0->...->rN polyline per arm, which tangled at 10
rounds and duplicated the left zigzag's round-order info. Make it a scatter that
just shows WHERE steered/healed land, labelling only r0 + last round. Persist the
base eval as an event so the loop's plot is reproducible offline, and add
scripts/plot_run.py to re-render trajectory.png from events.jsonl without re-running
the 3h loop (needed because the loop imports plot.py at start, so a plot fix never
reaches a running job).

Co-Authored-By: Claudypoo <288921227+claudypoo@users.noreply.github.com>

scripts/plot_run.py

@@ -0,0 +1,54 @@
+"""Re-render a run's trajectory plot from its events.jsonl, without re-running the loop.
+
+Why this exists: the loop imports plot.py at process start, so a plot-code fix never
+reaches an already-running job. events.jsonl persists every stage (base/steered/healed),
+so we can rebuild the `stages` list offline and call the CURRENT write_trajectory.
+
+    uv run python scripts/plot_run.py --run-dir out/20260604T172126_gemma-3-4b-it_kl_rev_s42/
+
+A run from before the `base` event was persisted has no base node; pass it explicitly
+(tyro reads negatives as flags, so use `=`):
+    ... --base-auth=-2.35 --base-care=-1.30 --base-coh=0.996
+"""
+import sys
+from pathlib import Path
+
+import srsly
+import tyro
+
+from steer_heal.plot import write_trajectory
+
+
+def main(run_dir: Path, base_auth: float | None = None,
+         base_care: float | None = None, base_coh: float | None = None):
+    events = list(srsly.read_jsonl(run_dir / "events.jsonl"))
+    by_stage = lambda s: [e for e in events if e["stage"] == s]
+
+    base_ev = by_stage("base")
+    if base_ev:
+        bm = base_ev[0]
+        base = {"auth_nats": bm["auth_nats"], "care_nats": bm["care_nats"], "coherence": bm["coherence"]}
+    else:
+        # older run: base wasn't persisted. require it on the CLI (fail fast, no silent default).
+        assert base_auth is not None, (
+            f"{run_dir}/events.jsonl has no `base` event (ran before run.py persisted it); "
+            "pass --base-auth/--base-care/--base-coh from the run's base eval log line."
+        )
+        base = {"auth_nats": base_auth, "care_nats": base_care, "coherence": base_coh}
+
+    stages = [{"round": "-", "stage": "base", "m": base}]
+    steered = {e["round"]: e for e in by_stage("steered_eval")}
+    healed = {e["round"]: e for e in by_stage("round")}
+    for rnd in sorted(healed):  # one steered + one healed per completed round, in order
+        for src, kind in [(steered, "steered"), (healed, "healed")]:
+            e = src[rnd]
+            stages.append({"round": rnd, "stage": kind,
+                           "m": {"auth_nats": e["auth_nats"], "care_nats": e["care_nats"],
+                                 "coherence": e["coherence"]}})
+
+    png = write_trajectory(run_dir, stages)
+    print(f"re-rendered {png} from {len(stages)} stages ({len(healed)} rounds)", file=sys.stderr)
+
+
+if __name__ == "__main__":
+    tyro.cli(main)