feat(agent): grounded control checker — compose judge -> ground gate

GroundedControlChecker<J: ControlJudge>::check(spec, regions, repo_id) judges each
candidate region and keeps only findings that survive the core grounding gate.
Generic over the judge so tests drive it with a deterministic stub — the
recognize->ground path is proven without an LLM (grounded snippet kept, ungrounded
dropped, non-violation yields nothing). 2 lib tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

compliance-agent/src/controls/checker.rs

@@ -0,0 +1,114 @@
+//! The grounded control checker: judge each candidate region for a control, then
+//! keep only the verdicts that survive the grounding gate.
+//!
+//! Generic over [`ControlJudge`] so tests drive it with a deterministic stub —
+//! the whole recognize → ground path is then exercised without an LLM. With the
+//! real judge, determinism comes from temperature 0 plus the gate.
+
+use compliance_core::control_check::{ground, CandidateRegion, ControlCheckSpec};
+use compliance_core::models::Finding;
+
+use super::judge::ControlJudge;
+
+/// Runs a [`ControlJudge`] over candidate regions and grounds the results.
+pub struct GroundedControlChecker<J> {
+    judge: J,
+}
+
+impl<J: ControlJudge> GroundedControlChecker<J> {
+    pub fn new(judge: J) -> Self {
+        Self { judge }
+    }
+
+    /// Judge every candidate region for `spec` and return the grounded findings.
+    /// A verdict that doesn't quote real code in its region is dropped by
+    /// [`ground`], so nothing fabricated reaches the caller.
+    pub async fn check(
+        &self,
+        spec: &ControlCheckSpec,
+        regions: &[CandidateRegion],
+        repo_id: &str,
+    ) -> Vec<Finding> {
+        let mut findings = Vec::new();
+        for region in regions {
+            let verdict = self.judge.judge(spec, region).await;
+            if let Some(finding) = ground(spec, region, &verdict, repo_id) {
+                findings.push(finding);
+            }
+        }
+        findings
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use compliance_core::control_check::LlmVerdict;
+    use compliance_core::models::finding::Severity;
+
+    /// Deterministic stub: returns a fixed verdict for every region, so the
+    /// recognize → ground composition is tested without an LLM.
+    struct StubJudge {
+        verdict: LlmVerdict,
+    }
+
+    impl ControlJudge for StubJudge {
+        async fn judge(&self, _spec: &ControlCheckSpec, _region: &CandidateRegion) -> LlmVerdict {
+            self.verdict.clone()
+        }
+    }
+
+    fn spec() -> ControlCheckSpec {
+        ControlCheckSpec {
+            control_id: "cra-ai-8".into(),
+            title: "No default passwords".into(),
+            requirement: "No default credentials".into(),
+            default_cwe: Some("CWE-798".into()),
+            severity: Severity::High,
+        }
+    }
+
+    fn region(content: &str) -> CandidateRegion {
+        CandidateRegion {
+            file: "src/auth.py".into(),
+            start_line: 1,
+            content: content.into(),
+        }
+    }
+
+    #[tokio::test]
+    async fn keeps_grounded_and_drops_ungrounded() {
+        let checker = GroundedControlChecker::new(StubJudge {
+            verdict: LlmVerdict {
+                violates: true,
+                snippet: "PASSWORD = \"admin\"".into(),
+                cwe: None,
+                confidence: 0.9,
+            },
+        });
+        let regions = vec![
+            region("x = 1\nPASSWORD = \"admin\"\n"), // quotes real code → grounded
+            region("totally unrelated code\n"),      // snippet absent → dropped
+        ];
+        let findings = checker.check(&spec(), &regions, "repo").await;
+        assert_eq!(findings.len(), 1);
+        assert_eq!(findings[0].rule_id.as_deref(), Some("cra-ai-8"));
+        assert_eq!(findings[0].line_number, Some(2));
+    }
+
+    #[tokio::test]
+    async fn non_violation_yields_nothing() {
+        let checker = GroundedControlChecker::new(StubJudge {
+            verdict: LlmVerdict {
+                violates: false,
+                snippet: String::new(),
+                cwe: None,
+                confidence: 0.0,
+            },
+        });
+        let findings = checker
+            .check(&spec(), &[region("PASSWORD = \"admin\"\n")], "repo")
+            .await;
+        assert!(findings.is_empty());
+    }
+}

compliance-agent/src/controls/mod.rs

@@ -5,8 +5,10 @@
 //! [`OscalControlsProvider`], which pulls breakpilot-compliance's OSCAL catalog
 //! and snapshots it locally.
 
+mod checker;
 mod judge;
 mod oscal_provider;
 
+pub use checker::GroundedControlChecker;
 pub use judge::{ControlJudge, LlmControlJudge, PROMPT_VERSION};
 pub use oscal_provider::OscalControlsProvider;