feat(cli): add --json to steer-report for machine-readable output paths

src/steerbench/cli.py

@@ -15,6 +15,7 @@
 from __future__ import annotations
 
 import argparse
+import json
 import subprocess
 import sys
 from pathlib import Path
@@ -101,6 +102,11 @@ def _build_parser() -> argparse.ArgumentParser:
         metavar="FUNCTION",
         help="run a Modal harness function (needs steerbench[gpu]) instead of rendering",
     )
+    parser.add_argument(
+        "--json",
+        action="store_true",
+        help="print the written artifact paths as a single JSON object (suppresses human text)",
+    )
     return parser
 
 
@@ -126,9 +132,12 @@ def main(argv: list[str] | None = None) -> int:
         out_dir=args.out,
         stem=args.stem,
     )
-    print("[steerbench] wrote:")
-    for kind, path in outputs.items():
-        print(f"  {kind:9s} {path}")
+    if args.json:
+        print(json.dumps({kind: str(path) for kind, path in outputs.items()}))
+    else:
+        print("[steerbench] wrote:")
+        for kind, path in outputs.items():
+            print(f"  {kind:9s} {path}")
     return 0
 
 

tests/test_cli.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 from pathlib import Path
 
 import pytest
@@ -37,6 +38,32 @@ def test_cli_renders_from_real_artifacts(tmp_path: Path) -> None:
     assert (out / "side_effects.csv").read_text().startswith("benchmark,")
 
 
+def test_cli_json_emits_artifact_paths(tmp_path: Path, capsys: pytest.CaptureFixture[str]) -> None:
+    pytest.importorskip("matplotlib")
+    out = tmp_path / "card"
+    rc = cli.main(
+        [
+            "--dose-csv",
+            str(_DOSE),
+            "--layer-csv",
+            str(_LAYER),
+            "--out",
+            str(out),
+            "--stem",
+            "report",
+            "--json",
+        ]
+    )
+    assert rc == 0
+    stdout = capsys.readouterr().out
+    # human "wrote:" lines are suppressed under --json.
+    assert "[steerbench] wrote:" not in stdout
+    payload = json.loads(stdout)
+    for key in ("markdown", "html", "dose_png", "layer_png"):
+        assert key in payload, f"missing artifact key: {key}"
+        assert Path(payload[key]).exists(), f"artifact path does not exist: {payload[key]}"
+
+
 def test_cli_errors_on_missing_csv(tmp_path: Path) -> None:
     with pytest.raises(SystemExit):
         cli.main(["--dose-csv", str(tmp_path / "nope.csv"), "--out", str(tmp_path / "o")])