fix(cli): catch JSONDecodeError, exit 2 with clean message

Adds JSONDecodeError handler in `_cmd_verify` so a structurally invalid log surfaces `structurally invalid log: …` on stderr and exits 2, instead of leaking a Python traceback. Locks the UX contract with a subprocess-level test that asserts 'Traceback' is absent from stderr.

Closes #15. Same bug was also caught in #14 (closed as duplicate).

Co-authored-by: akmhatey-ai <akmhatey-ai@users.noreply.github.com>

Author: akmhatey-ai

falsify_inspect/cli.py

@@ -43,6 +43,9 @@ def _cmd_verify(args: argparse.Namespace) -> int:
     except PRMLVerificationError as exc:
         sys.stderr.write(f"verification error: {exc}\n")
         return 3
+    except json.JSONDecodeError as exc:
+        sys.stderr.write(f"structurally invalid log: {exc}\n")
+        return 2
     except FileNotFoundError as exc:
         sys.stderr.write(f"log not found: {exc}\n")
         return 2

tests/test_cli.py

@@ -0,0 +1,35 @@
+"""Tests for falsify_inspect.cli."""
+
+import subprocess
+import sys
+from pathlib import Path
+
+
+def test_verify_malformed_json_exits_2_without_traceback(tmp_path: Path):
+    log_path = tmp_path / "broken.log"
+    log_path.write_text("not valid json", encoding="utf-8")
+
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-m",
+            "falsify_inspect.cli",
+            "verify",
+            str(log_path),
+            "--hash",
+            "deadbeef",
+            "--threshold",
+            "0.5",
+            "--threshold-direction",
+            ">=",
+            "--pre-registered",
+            "2026-01-01T00:00:00Z",
+        ],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+    assert result.returncode == 2
+    assert "structurally invalid log:" in result.stderr
+    assert "Traceback" not in result.stderr