diff --git a/experiments/check_plateau_physics.py b/experiments/check_plateau_physics.py
new file mode 100644
index 0000000..1a94a51
--- /dev/null
+++ b/experiments/check_plateau_physics.py
@@ -0,0 +1,203 @@
+#!/usr/bin/env python3
+"""Report a plateau endpoint and gate strict solver convergence plus eight virials.
+
+Usage: check_plateau_physics.py RESULT_FOLDER
+Exit 0: solver_and_virial_milestone passes. Exit 3: it does not pass.
+Exit 2: required endpoint data is missing or malformed. Standard-library only.
+Local errors remain measurements; passing this gate is not full physical validation.
+"""
+
+import argparse
+import csv
+import json
+import math
+from pathlib import Path
+import sys
+
+
+THRESHOLD = 1.0e-5
+QUADRATURES = (14, 18)
+VIRIALS = {
+    "pressure_from_enthalpy_energy": "enthalpy_virial_error",
+    "pressure_from_enthalpy_force": "enthalpy_force_virial_error",
+    "pressure_from_density_energy": "virial_error",
+    "pressure_from_density_force": "force_virial_error",
+}
+SIGN_METRICS = (
+    "minimum_density", "maximum_density", "negative_density_samples",
+    "negative_density_mass_fraction", "negative_density_volume_fraction",
+    "minimum_enthalpy", "maximum_enthalpy", "negative_enthalpy_samples",
+    "negative_enthalpy_volume_fraction",
+)
+CONSERVATION_METRICS = (
+    "mass", "mass_absolute_error", "angular_momentum_z", "angular_momentum_absolute_error",
+)
+LOCAL_METRICS = (
+    "eos_density_mismatch_maximum", "eos_density_mismatch_maximum_scaled",
+    "eos_density_mismatch_rms", "eos_density_mismatch_rms_scaled",
+    "bernoulli_raw_rms", "bernoulli_raw_rms_scaled",
+    "bernoulli_mean_subtracted_rms", "bernoulli_mean_subtracted_rms_scaled",
+    "bernoulli_sampled_range", "hydrostatic_gradient_rms",
+)
+PRESSURE_METRICS = (
+    "pressure_from_density_defined_everywhere", "pressure_integral",
+    "pressure_from_enthalpy_defined_everywhere", "enthalpy_pressure_integral",
+)
+REQUIRED_METRICS = (
+    *VIRIALS.values(), *SIGN_METRICS, *CONSERVATION_METRICS,
+    *LOCAL_METRICS, *PRESSURE_METRICS, "complete_volume_measurement",
+)
+
+
+def measurement(value):
+    """Keep JSON standard-compliant without losing the reason for a null value."""
+    result = {"value": value if math.isfinite(value) else None, "finite": math.isfinite(value)}
+    if not result["finite"]:
+        result["nonfinite_value"] = "nan" if math.isnan(value) else ("+inf" if value > 0 else "-inf")
+    return result
+
+
+def read_metadata(path):
+    result = {}
+    for line in path.read_text().splitlines():
+        if not line.strip():
+            continue
+        if "=" not in line:
+            raise ValueError(f"Malformed metadata line in {path}: {line!r}")
+        key, value = line.split("=", 1)
+        if not key or key in result:
+            raise ValueError(f"Empty or duplicate metadata key in {path}: {key!r}")
+        result[key] = value
+    if result.get("converged") not in ("0", "1"):
+        raise ValueError("metadata.txt must contain a completed converged=0 or converged=1 result")
+    if "accepted_steps" not in result or int(result["accepted_steps"]) < 0:
+        raise ValueError("metadata.txt must contain a nonnegative accepted_steps count")
+    return result
+
+
+def read_physical(path):
+    result = {q: {} for q in QUADRATURES}
+    with path.open(newline="") as stream:
+        reader = csv.DictReader(stream)
+        if reader.fieldnames != ["quadrature", "metric", "value"]:
+            raise ValueError("final_physical.csv requires the header quadrature,metric,value")
+        for row in reader:
+            if None in row or any(value is None for value in row.values()):
+                raise ValueError("Malformed row in final_physical.csv")
+            q = int(row["quadrature"])
+            if q not in result:
+                continue
+            key = row["metric"]
+            if not key or key in result[q]:
+                raise ValueError(f"Empty or duplicate physical metric at quadrature {q}: {key!r}")
+            result[q][key] = float(row["value"])
+    for q, values in result.items():
+        missing = [key for key in REQUIRED_METRICS if key not in values]
+        if missing:
+            raise ValueError(f"Missing quadrature {q} endpoint metrics: {', '.join(missing)}")
+        for key in ("complete_volume_measurement", "pressure_from_density_defined_everywhere",
+                    "pressure_from_enthalpy_defined_everywhere"):
+            if values[key] not in (0.0, 1.0):
+                raise ValueError(f"Invalid boolean metric at quadrature {q}: {key}")
+        for key in VIRIALS.values():
+            if math.isfinite(values[key]) and values[key] < 0:
+                raise ValueError(f"A virial error must be nonnegative: quadrature {q}, {key}")
+    return result
+
+
+def pressure_report(values, kind):
+    flag = values[f"pressure_from_{kind}_defined_everywhere"] == 1.0
+    integral = values["pressure_integral" if kind == "density" else "enthalpy_pressure_integral"]
+    return {
+        "defined_at_all_samples": flag,
+        "integral": measurement(integral),
+        "valid": flag and math.isfinite(integral),
+    }
+
+
+def negative_samples_detected(values, kind):
+    minimum = values[f"minimum_{kind}"]
+    count = values[f"negative_{kind}_samples"]
+    if not math.isfinite(minimum) or not math.isfinite(count):
+        return None
+    return minimum < 0.0 or count > 0.0
+
+
+def assess(folder):
+    meta = read_metadata(folder / "metadata.txt")
+    physical = read_physical(folder / "final_physical.csv")
+    per_quadrature = {}
+    all_virials_pass = True
+    for q, values in physical.items():
+        complete = values["complete_volume_measurement"] == 1.0
+        pressure = {kind: pressure_report(values, kind) for kind in ("enthalpy", "density")}
+        virials = {}
+        for name, key in VIRIALS.items():
+            value = values[key]
+            kind = "density" if "density" in name else "enthalpy"
+            check = measurement(value)
+            if not complete or not pressure[kind]["valid"] or not math.isfinite(value):
+                check["status"] = "undefined"
+                check["reason"] = (
+                    "incomplete_volume_measurement" if not complete else
+                    "pressure_not_defined_or_finite" if not pressure[kind]["valid"] else
+                    "nonfinite_virial"
+                )
+            else:
+                check["status"] = "pass" if value <= THRESHOLD else "fail"
+            all_virials_pass = all_virials_pass and check["status"] == "pass"
+            virials[name] = check
+        per_quadrature[str(q)] = {
+            "complete_volume_measurement": complete,
+            "virials": virials,
+            "pressure": pressure,
+            "sampled_signs": {
+                "negative_density_detected": negative_samples_detected(values, "density"),
+                "negative_enthalpy_detected": negative_samples_detected(values, "enthalpy"),
+                **{key: measurement(values[key]) for key in SIGN_METRICS},
+            },
+            "conservation": {key: measurement(values[key]) for key in CONSERVATION_METRICS},
+            "local_measurements_without_acceptance_tolerances": {
+                key: measurement(values[key]) for key in LOCAL_METRICS
+            },
+        }
+    strict_converged = meta["converged"] == "1"
+    passed = strict_converged and all_virials_pass
+    report = {
+        "schema_version": 1,
+        "result_folder": str(folder.resolve()),
+        "solver_and_virial_milestone": "pass" if passed else "fail",
+        "strict_solver": {
+            "converged": strict_converged,
+            "accepted_steps": int(meta["accepted_steps"]),
+            "failure": meta.get("failure"),
+            "absolute_tolerance": meta.get("atol"),
+            "relative_tolerance": meta.get("rtol"),
+        },
+        "virial_threshold": THRESHOLD,
+        "all_eight_virial_checks_pass": all_virials_pass,
+        "quadratures": per_quadrature,
+        "interpretation": [
+            "The milestone requires strict recorded solver convergence and all four defined, finite virial errors <= 1e-5 at both quadratures.",
+            "The milestone is not full physical validation. Mass/J errors and local EOS/Bernoulli measurements have no acceptance tolerances here.",
+            "Density and enthalpy signs are quadrature samples; sampled extrema and local errors are not certified pointwise bounds.",
+            "An undefined pressure-from-density virial is kept separate from a finite virial that exceeds the threshold.",
+        ],
+    }
+    return report, 0 if passed else 3
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("result_folder", type=Path)
+    args = parser.parse_args()
+    try:
+        report, code = assess(args.result_folder)
+    except (OSError, ValueError, csv.Error) as error:
+        report, code = {"schema_version": 1, "input_error": str(error)}, 2
+    print(json.dumps(report, indent=2, allow_nan=False))
+    return code
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/experiments/check_plateau_physics_README.md b/experiments/check_plateau_physics_README.md
new file mode 100644
index 0000000..1f786b1
--- /dev/null
+++ b/experiments/check_plateau_physics_README.md
@@ -0,0 +1,30 @@
+# Plateau endpoint milestone checker
+
+Run the standalone standard-library script with one completed result folder:
+
+```sh
+python3 experiments/check_plateau_physics.py /absolute/path/to/plateau-result
+```
+
+It reads `metadata.txt` and `final_physical.csv` and prints standard JSON. Exit codes:
+
+- **0:** `solver_and_virial_milestone=pass`: recorded strict solver convergence and all eight defined, finite virial errors at or below 1e-5.
+- **3:** those milestone checks do not all pass, including an undefined pressure integral.
+- **2:** missing or malformed required endpoint data, including an incomplete quadrature table or missing convergence outcome.
+
+The eight checks comprise energy and force virials with both P(h) and P(rho), each at quadrature orders 14 and 18. An undefined check is distinguished from a finite check exceeding the threshold. Pressure validity, density/enthalpy signs, negative-density budgets, mass/J errors, and local EOS/Bernoulli measurements are reported separately. Nonfinite numbers become JSON null with a retained finite flag and NaN/infinity classification.
+
+Passing this gate is **not full physical validation**. No new tolerance is assigned to mass/J or local errors. Sampled signs and extrema are not certified pointwise bounds. The script trusts the diagnostic's recorded convergence flag and physical measurements; it does not reconstruct a model, validate provenance, or independently recompute integrals. It does not inspect or modify production code.
+
+Verification on the September 16 campaign:
+
+| Completed case | Expected and observed exit | Distinction checked |
+| --- | ---: | --- |
+| n=1, J=0.05, no central constraint, restart 160 | 0 | Strict convergence and all virials pass |
+| Same model, restart 40 | 3 | Virials pass, strict convergence fails |
+| n=1.5, J=0, no central constraint, restart 160 | 3 | P(h) virials pass; P(rho) is undefined |
+| n=3 initial seed | 3 | P(h) virials exceed the threshold |
+
+Threshold equality, one virial just above threshold, and missing required data
+were also checked. Detailed verification JSON and reports remain with the raw
+campaign artifacts in the audit workspace.
diff --git a/experiments/plateau_diagnostic_README.md b/experiments/plateau_diagnostic_README.md
index ce9a6bc..c0a8536 100644
--- a/experiments/plateau_diagnostic_README.md
+++ b/experiments/plateau_diagnostic_README.md
@@ -129,3 +129,9 @@ folders should remain outside source commits; retain compact result tables and
 reproduction instructions with each hypothesis branch. The controls omit the
 central phase at n=1 and n=1.5. A separate n=3 control retains it to fix homology;
 the production model API does not insert it implicitly.
+
+Check a completed endpoint with
+`python3 experiments/check_plateau_physics.py /absolute/path/to/result-folder`.
+This gates strict recorded solver convergence and all eight finite virial errors
+at 1e-5, while reporting local field errors separately. See
+`check_plateau_physics_README.md` for the exit codes and interpretation limits.
diff --git a/experiments/run_plateau_campaign.py b/experiments/run_plateau_campaign.py
index 68e85e0..78fcf2f 100644
--- a/experiments/run_plateau_campaign.py
+++ b/experiments/run_plateau_campaign.py
@@ -125,7 +125,10 @@ def main():
         state_files = {}
         for i, word in enumerate(case['arguments']):
             if word == '--probe-state':
-                path = Path(case['arguments'][i + 1]).resolve()
+                path = Path(case['arguments'][i + 1])
+                if not path.is_absolute():
+                    path = source / path
+                path = path.resolve()
                 state_files[str(path)] = digest(path)
         print('START', name, flush=True)
         start = time.monotonic()
@@ -140,6 +143,11 @@ def main():
                 record['timed_out'] = True
                 record['exit_code'] = None
         record.update(seconds=time.monotonic() - start, finished_utc=utc())
+        record['output_hashes'] = {
+            name: digest(folder / name)
+            for name in ('accepted_state.txt', 'layout.csv', 'metadata.txt', 'final_physical.csv')
+            if (folder / name).is_file()
+        }
         write_json(output / (name + '_run.json'), record)
         summaries.append({**record, **summarize(folder)})
         write_json(output / 'summary.json', summaries)