scripts/disk-gc-plan.py

@@ -59,6 +59,11 @@ def load_report_only_guests(contract_path: pathlib.Path) -> list[dict]:
             guests = data.get("report_only_guests") or []
             if not isinstance(guests, list):
                 raise SystemExit("report_only_guests must be a list")
+            if not guests:
+                raise SystemExit(
+                    "report_only_guests is empty or missing - refusing to plan GC "
+                    "without the report-only gate"
+                )
             for guest in guests:
                 if not isinstance(guest, dict) or not _keys(guest):
                     raise SystemExit(

tests/test_disk_gc_report_only.py

@@ -124,6 +124,22 @@ def test_exclusion_entry_without_identity_fails_closed(tmp_path):
     assert "identity" in proc.stderr.lower(), proc.stderr
 
 
+def test_empty_exclusion_block_fails_closed(tmp_path):
+    """An emptied report_only_guests list must break the run, not disable the gate."""
+    contract = tmp_path / "empty.prose.md"
+    contract.write_text("```yaml\nreport_only_guests: []\n```\n")
+    scan_file = tmp_path / "scan.json"
+    scan_file.write_text(json.dumps([{"ct": 111, "usage_pct": 97}]))
+    proc = subprocess.run(
+        [sys.executable, str(PLAN), "--scan", str(scan_file),
+         "--contract", str(contract), "--json"],
+        capture_output=True, text=True,
+    )
+    assert proc.returncode != 0, proc.stdout
+    assert "gc-executor" not in proc.stdout
+    assert "report-only gate" in proc.stderr.lower(), proc.stderr
+
+
 def _plan_with_contract(scan, contract_text, tmp_path, name):
     contract = tmp_path / name
     contract.write_text(contract_text)
@@ -152,7 +168,13 @@ def test_gate_is_read_from_the_contract_block(tmp_path):
         "    reason: \"fixture reason\"\n"
         "```\n"
     )
-    without_gate = "```yaml\nreport_only_guests: []\n```\n"
+    without_gate = (
+        "```yaml\n"
+        "report_only_guests:\n"
+        "  - guest: 999\n"
+        "    reason: \"fixture excludes a different guest\"\n"
+        "```\n"
+    )
 
     gated = _plan_with_contract(scan, with_gate, tmp_path, "gated.prose.md")
     assert gated[0]["action"] == "report-only", gated