fix(strix): classify ModelBehaviorError with zero findings as backend skip

.github/workflows/strix.yml

@@ -839,7 +839,8 @@ jobs:
           # exit 1 both for genuine blocking vulnerabilities AND for
           # LLM-backend-unavailable outcomes (GitHub Models "Too many requests"
           # rate limits, OpenAI quota starvation, 413 tokens_limit_reached
-          # token-cap, connection/warm-up failures) that could not complete a scan. A backend outage is CI
+          # token-cap, connection/warm-up failures, ModelBehaviorError
+          # classifier flakes with zero findings) that could not complete a scan. A backend outage is CI
           # infrastructure noise, not a security finding, so it must not fail
           # the required check and block merges.
           strix_run_log="$RUNNER_TEMP/strix_gate_console.log"
@@ -861,7 +862,7 @@ jobs:
           fi
 
           # Recognized signals that the LLM backend was unavailable / starved.
-          backend_unavailable_signal='RateLimitError|Too many requests\. For more on scraping GitHub|exceeded your current quota|insufficient_quota|billing details|"status"[[:space:]]*:[[:space:]]*"RESOURCE_EXHAUSTED"|tokens_limit_reached|Request body too large|Max size:[[:space:]]*[0-9]+[[:space:]]+tokens|Error code:[[:space:]]*413|LLM CONNECTION FAILED|Could not establish connection to the language model|LLM warm-up failed|Configured model and fallback models were unavailable|Configured Vertex model and fallback models were unavailable|emitted provider infrastructure or failure-signal output|before provider infrastructure failure|litellm(\.exceptions)?\.NotFoundError[^[:cntrl:]]*Nvidia_nimException[^[:cntrl:]]*Error code:[[:space:]]*404'
+          backend_unavailable_signal='RateLimitError|Too many requests\. For more on scraping GitHub|exceeded your current quota|insufficient_quota|billing details|"status"[[:space:]]*:[[:space:]]*"RESOURCE_EXHAUSTED"|tokens_limit_reached|Request body too large|Max size:[[:space:]]*[0-9]+[[:space:]]+tokens|Error code:[[:space:]]*413|LLM CONNECTION FAILED|Could not establish connection to the language model|LLM warm-up failed|Configured model and fallback models were unavailable|Configured Vertex model and fallback models were unavailable|emitted provider infrastructure or failure-signal output|before provider infrastructure failure|litellm(\.exceptions)?\.NotFoundError[^[:cntrl:]]*Nvidia_nimException[^[:cntrl:]]*Error code:[[:space:]]*404|ModelBehaviorError'
           # Any evidence that a vulnerability was actually reported. Its presence
           # forces a hard failure so real findings are NEVER downgraded. Keep the
           # severity branch anchored away from identifiers so environment lines

CHANGELOG.md

@@ -26,6 +26,9 @@ Semantic Versioning where the repository publishes a release.
 
 ### Fixed
 
+- Classify Strix `ModelBehaviorError` with `Vulnerabilities 0` as a
+  backend-unavailable skip so the required check does not fail-closed on
+  an LLM classifier flake. `Vulnerabilities [1-9]` still fail the check.
 - Materialized base Python locks only when every package line is an exact SHA-256 pin or a bounded relative `-r`/`--requirement` include. A lone `--require-hashes` directive, a dotted include such as `./lock.txt`, or `-r other-hashes.txt` no longer enters the trusted build context.
 - Refused a conflict-scope repository root whose immediate parent is a symbolic link, so a swapped parent cannot redirect the canonical worktree after the last-component check (CWE-367).
 - Bounded the Strix quality self-test's deterministic timeout fixtures to 3-second process and 5-second fake-sleep budgets so exact-head policy evidence completes inside the existing job limit without changing production Strix scanner timeouts, providers, credentials, or review semantics.

tests/test_strix_modelbehaviorerror_classifier.py

@@ -0,0 +1,105 @@
+"""ModelBehaviorError is infrastructure noise when no vulnerability is reported.
+
+A Strix run that exits 1 with ModelBehaviorError and Vulnerabilities 0 must
+neutralize. Vulnerabilities [1-9] stay fail-closed even when the same
+exception is present. Do not weaken that gate.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+import tempfile
+import unittest
+from pathlib import Path
+
+
+REPOSITORY_ROOT = Path(__file__).resolve().parents[1]
+STRIX_WORKFLOW = REPOSITORY_ROOT / ".github" / "workflows" / "strix.yml"
+
+
+def _workflow_signal_pattern(workflow: str, variable_name: str) -> str:
+    """Extract one single-quoted POSIX ERE assigned in the Strix workflow."""
+
+    match = re.search(
+        rf"(?m)^\s+{re.escape(variable_name)}='([^']+)'$",
+        workflow,
+    )
+    if match is None:
+        raise AssertionError(f"missing workflow signal: {variable_name}")
+    return match.group(1)
+
+
+def _workflow_neutralizes(log_text: str) -> bool:
+    """Execute the outer workflow's backend-neutralization condition."""
+
+    workflow = STRIX_WORKFLOW.read_text(encoding="utf-8")
+    backend_pattern = _workflow_signal_pattern(
+        workflow,
+        "backend_unavailable_signal",
+    )
+    vulnerability_pattern = _workflow_signal_pattern(
+        workflow,
+        "reported_vulnerability_signal",
+    )
+    with tempfile.TemporaryDirectory(prefix="strix-modelbehavior-") as temp_dir:
+        log_path = Path(temp_dir) / "strix.log"
+        log_path.write_text(log_text, encoding="utf-8")
+        backend = subprocess.run(
+            ["grep", "-Eiq", backend_pattern, str(log_path)],
+            check=False,
+            capture_output=True,
+            text=True,
+        )
+        vulnerability = subprocess.run(
+            ["grep", "-Eiq", vulnerability_pattern, str(log_path)],
+            check=False,
+            capture_output=True,
+            text=True,
+        )
+    if backend.returncode not in {0, 1}:
+        raise AssertionError(backend.stderr)
+    if vulnerability.returncode not in {0, 1}:
+        raise AssertionError(vulnerability.stderr)
+    return backend.returncode == 0 and vulnerability.returncode == 1
+
+
+class StrixModelBehaviorErrorClassifierTests(unittest.TestCase):
+    """Neutralize ModelBehaviorError flakes; keep Vulnerabilities [1-9] blocking."""
+
+    def test_model_behavior_error_with_zero_findings_is_neutral(self) -> None:
+        self.assertTrue(
+            _workflow_neutralizes(
+                "litellm.exceptions.ModelBehaviorError: invalid tool call\n"
+                "Vulnerabilities 0\n"
+            )
+        )
+
+    def test_model_behavior_error_with_one_finding_stays_fail_closed(self) -> None:
+        self.assertFalse(
+            _workflow_neutralizes(
+                "litellm.exceptions.ModelBehaviorError: invalid tool call\n"
+                "Vulnerabilities 1\n"
+            )
+        )
+
+    def test_model_behavior_error_with_nine_findings_stays_fail_closed(self) -> None:
+        self.assertFalse(
+            _workflow_neutralizes(
+                "ModelBehaviorError\n"
+                "Vulnerabilities 9\n"
+            )
+        )
+
+    def test_zero_findings_without_backend_signal_is_not_neutral(self) -> None:
+        self.assertFalse(_workflow_neutralizes("Vulnerabilities 0\nscan incomplete\n"))
+
+    def test_workflow_keeps_fail_closed_vulnerability_range(self) -> None:
+        workflow = STRIX_WORKFLOW.read_text(encoding="utf-8")
+        self.assertIn("ModelBehaviorError", workflow)
+        self.assertIn("Vulnerabilities[[:space:]]+[1-9]", workflow)
+        self.assertIn('! grep -Eiq "$reported_vulnerability_signal"', workflow)
+
+
+if __name__ == "__main__":
+    unittest.main()