feat(three-stage-scan): add aliased-sink mutation the regex scan misses

.kiro/specs/three-stage-scan/tasks.md

@@ -172,7 +172,7 @@ This plan ships the three-stage scan without rebuilding CWE policy or the regex
   - _Requirements: 8.1_
   - _Boundary: Benchmark Harness_
 
-- [ ] 7.2 (P) Add a mutation of a known sink that a same-line pattern does not match
+- [x] 7.2 (P) Add a mutation of a known sink that a same-line pattern does not match
   - At least one wrapper or intermediate-variable mutation exists per the evaluation plan.
   - Observable completion: stage 1 misses the mutation; the case is listed as expected in a split-sink or mutation manifest.
   - _Requirements: 8.2_

benchmarks/fixtures/mutation-python/app.py

@@ -0,0 +1,13 @@
+"""Mutation of os.system: the callable is aliased before use so a same-line regex misses it."""
+import os
+
+from flask import Flask, request
+
+app = Flask(__name__)
+run_cmd = os.system
+
+
+@app.get("/ping")
+def ping():
+    host = request.args["host"]
+    return run_cmd("ping -c 1 " + host)  # CWE-78 mutation: os.system aliased before the call

benchmarks/manifests/mutation-python.toml

@@ -0,0 +1,20 @@
+name = "mutation-python"
+language = "python_web"
+frameworks = ["flask"]
+setup = ["pip install flask"]
+modes = ["quick", "standard"]
+known_noise = []
+baselines = []
+
+[source]
+type = "local"
+path = "../fixtures/mutation-python"
+
+[[expected]]
+cwe = "CWE-78"
+class = "command injection"
+path = "app.py"
+line = 13
+function = "ping"
+sink = "run_cmd"
+evidence = "aliased os.system runs an attacker-controlled command"

tests/test_benchmark.py

@@ -63,6 +63,7 @@ def test_repository_benchmark_manifests_load_and_point_to_fixtures() -> None:
         "java-web-smoke.toml",
         "javascript-node-web-smoke.toml",
         "javascript-vulnerable.toml",
+        "mutation-python.toml",
         "python-vulnerable.toml",
         "python-web-smoke.toml",
         "split-sink-c.toml",

tests/test_mutation_fixtures.py

@@ -0,0 +1,46 @@
+"""Mutation fixtures: stage-1 same-line patterns must miss the aliased sink (requirement 8.2)."""
+
+from pathlib import Path
+
+from openultrasast.benchmark import BenchmarkRun, evaluate_benchmark, load_benchmark_manifest, resolve_benchmark_source
+from openultrasast.findings import StaticFinding, quick_scan_findings
+from openultrasast.gate import LANGUAGE_MANIFESTS
+from openultrasast.preprocess import preprocess_repository
+from openultrasast.rank import rank_targets
+
+MANIFEST = Path("benchmarks/manifests/mutation-python.toml")
+
+
+def _quick_scan(target: Path) -> list[StaticFinding]:
+    _, targets = preprocess_repository(target)
+    return quick_scan_findings(target, targets, rank_targets(targets))
+
+
+def test_stage1_misses_aliased_os_system_mutation() -> None:
+    manifest = load_benchmark_manifest(MANIFEST)
+    target = resolve_benchmark_source(MANIFEST, manifest)
+    planted = [item for item in manifest.expected if item.rule_id is None]
+    assert planted, "mutation manifest must document a stage-1 miss without rule_id"
+    expected = planted[0]
+    assert expected.sink == "run_cmd"
+    assert expected.line is not None
+
+    source = (target / expected.path).read_text()
+    lines = source.splitlines()
+    assert "os.system" in source
+    assert "os.system(" not in lines[expected.line - 1]
+    assert "run_cmd(" in lines[expected.line - 1]
+
+    findings = _quick_scan(target)
+    on_line = [finding for finding in findings if finding.path == expected.path and finding.line == expected.line]
+    assert on_line == [], f"stage-1 hit the mutation on {expected.path}:{expected.line}: {on_line}"
+
+    run = BenchmarkRun(benchmark_run_id="mutation", root=Path("/tmp/mutation"), manifest=manifest)
+    result = evaluate_benchmark(run=run, mode="quick", findings=findings, scan_id=None, scan_run_dir=None)
+    missed = {(miss.path, miss.cwe, miss.rule_id) for miss in result.misses}
+    assert (expected.path, expected.cwe, None) in missed
+
+
+def test_mutation_fixture_is_outside_stage1_gate_corpus() -> None:
+    listed = {name for names in LANGUAGE_MANIFESTS.values() for name in names}
+    assert "mutation-python" not in listed