diff --git a/compliance-agent/src/controls/index.rs b/compliance-agent/src/controls/index.rs
new file mode 100644
index 0000000..494e918
--- /dev/null
+++ b/compliance-agent/src/controls/index.rs
@@ -0,0 +1,110 @@
+//! In-memory embedding index over the control corpus, for region → control
+//! retrieval.
+//!
+//! At master-control scale (~13.6k) findings can't be mapped by CWE (the master
+//! controls carry none), so we map by *similarity*: embed each control's
+//! requirement text once, then for a code region pull the top-K nearest controls
+//! to hand to the grounded judge. This is the retrieval half of the semantic path.
+
+use compliance_core::control_check::ControlCheckSpec;
+use compliance_core::error::CoreError;
+
+use crate::llm::LlmClient;
+
+/// A control spec paired with its requirement-text embedding.
+pub struct ControlIndex {
+    entries: Vec<(ControlCheckSpec, Vec<f64>)>,
+}
+
+impl ControlIndex {
+    /// Build directly from precomputed embeddings (used by tests + callers that
+    /// already embedded the corpus).
+    pub fn from_embeddings(entries: Vec<(ControlCheckSpec, Vec<f64>)>) -> Self {
+        Self { entries }
+    }
+
+    /// Build by embedding each control's requirement text.
+    pub async fn build(llm: &LlmClient, specs: Vec<ControlCheckSpec>) -> Result<Self, CoreError> {
+        if specs.is_empty() {
+            return Ok(Self {
+                entries: Vec::new(),
+            });
+        }
+        let texts: Vec<String> = specs.iter().map(|s| s.requirement.clone()).collect();
+        let embeddings = llm
+            .embed(texts)
+            .await
+            .map_err(|e| CoreError::Llm(e.to_string()))?;
+        Ok(Self {
+            entries: specs.into_iter().zip(embeddings).collect(),
+        })
+    }
+
+    pub fn len(&self) -> usize {
+        self.entries.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.entries.is_empty()
+    }
+
+    /// The top-`k` control specs whose embedding is nearest (cosine) to `query`.
+    pub fn nearest(&self, query: &[f64], k: usize) -> Vec<ControlCheckSpec> {
+        let mut scored: Vec<(f64, &ControlCheckSpec)> = self
+            .entries
+            .iter()
+            .map(|(spec, emb)| (cosine(query, emb), spec))
+            .collect();
+        scored.sort_by(|a, b| b.0.total_cmp(&a.0));
+        scored.into_iter().take(k).map(|(_, s)| s.clone()).collect()
+    }
+}
+
+/// Cosine similarity; 0.0 for length-mismatched, empty, or zero vectors.
+fn cosine(a: &[f64], b: &[f64]) -> f64 {
+    if a.len() != b.len() || a.is_empty() {
+        return 0.0;
+    }
+    let dot: f64 = a.iter().zip(b).map(|(x, y)| x * y).sum();
+    let na: f64 = a.iter().map(|x| x * x).sum();
+    let nb: f64 = b.iter().map(|x| x * x).sum();
+    if na == 0.0 || nb == 0.0 {
+        return 0.0;
+    }
+    dot / (na.sqrt() * nb.sqrt())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use compliance_core::models::finding::Severity;
+
+    fn spec(id: &str) -> ControlCheckSpec {
+        ControlCheckSpec {
+            control_id: id.into(),
+            title: id.into(),
+            requirement: id.into(),
+            default_cwe: None,
+            severity: Severity::Medium,
+        }
+    }
+
+    #[test]
+    fn nearest_ranks_by_cosine() {
+        let index = ControlIndex::from_embeddings(vec![
+            (spec("a"), vec![1.0, 0.0]),
+            (spec("b"), vec![0.0, 1.0]),
+            (spec("c"), vec![0.7, 0.7]),
+        ]);
+        let hits = index.nearest(&[0.9, 0.1], 2);
+        assert_eq!(hits.len(), 2);
+        assert_eq!(hits[0].control_id, "a"); // closest to [0.9,0.1]
+    }
+
+    #[test]
+    fn cosine_edges_are_zero() {
+        assert_eq!(cosine(&[1.0], &[1.0, 2.0]), 0.0); // length mismatch
+        assert_eq!(cosine(&[0.0, 0.0], &[1.0, 1.0]), 0.0); // zero vector
+        assert!((cosine(&[1.0, 0.0], &[1.0, 0.0]) - 1.0).abs() < 1e-9); // identical
+    }
+}
diff --git a/compliance-agent/src/controls/mod.rs b/compliance-agent/src/controls/mod.rs
index f47894c..fcc73a3 100644
--- a/compliance-agent/src/controls/mod.rs
+++ b/compliance-agent/src/controls/mod.rs
@@ -6,13 +6,17 @@
 //! and snapshots it locally.
 
 mod checker;
+mod index;
 mod judge;
 mod oscal_provider;
 mod scan_triage;
+mod semantic;
 mod triage;
 
 pub use checker::GroundedControlChecker;
+pub use index::ControlIndex;
 pub use judge::{ControlJudge, LlmControlJudge, PROMPT_VERSION};
 pub use oscal_provider::OscalControlsProvider;
-pub use scan_triage::triage_repo_findings;
+pub use scan_triage::{semantic_stamp_findings, triage_repo_findings};
+pub use semantic::SemanticControlChecker;
 pub use triage::{ControlTriage, TriageOutcome};
diff --git a/compliance-agent/src/controls/oscal_provider.rs b/compliance-agent/src/controls/oscal_provider.rs
index 0b484d3..84dfc8d 100644
--- a/compliance-agent/src/controls/oscal_provider.rs
+++ b/compliance-agent/src/controls/oscal_provider.rs
@@ -43,20 +43,20 @@ impl OscalControlsProvider {
         }
     }
 
-    fn catalog_url(&self, framework: ComplianceFramework) -> String {
+    fn catalog_url(&self, framework: &str) -> String {
         format!(
             "{}/api/compliance/v1/oscal/catalog?framework={framework}",
             self.base_url.trim_end_matches('/')
         )
     }
 
-    fn snapshot_path(&self, framework: ComplianceFramework) -> PathBuf {
+    fn snapshot_path(&self, framework: &str) -> PathBuf {
         self.snapshot_dir
             .join(format!("oscal-catalog-{framework}.json"))
     }
 
-    /// Fetch the raw catalog bytes for a framework over HTTP.
-    async fn fetch_raw(&self, framework: ComplianceFramework) -> Result<Vec<u8>, CoreError> {
+    /// Fetch the raw catalog bytes for a framework token over HTTP.
+    async fn fetch_raw(&self, framework: &str) -> Result<Vec<u8>, CoreError> {
         let mut req = self.http.get(self.catalog_url(framework));
         if let Some(token) = &self.token {
             req = req.bearer_auth(token.expose_secret());
@@ -78,11 +78,7 @@ impl OscalControlsProvider {
     }
 
     /// Write a catalog snapshot atomically (temp file + rename).
-    async fn write_snapshot(
-        &self,
-        framework: ComplianceFramework,
-        raw: &[u8],
-    ) -> Result<(), CoreError> {
+    async fn write_snapshot(&self, framework: &str, raw: &[u8]) -> Result<(), CoreError> {
         tokio::fs::create_dir_all(&self.snapshot_dir).await?;
         let path = self.snapshot_path(framework);
         let tmp = path.with_extension("json.tmp");
@@ -92,10 +88,7 @@ impl OscalControlsProvider {
     }
 
     /// Read a previously written snapshot, if one exists.
-    async fn read_snapshot(
-        &self,
-        framework: ComplianceFramework,
-    ) -> Result<Option<OscalDocument>, CoreError> {
+    async fn read_snapshot(&self, framework: &str) -> Result<Option<OscalDocument>, CoreError> {
         match tokio::fs::read(self.snapshot_path(framework)).await {
             Ok(raw) => Ok(Some(serde_json::from_slice(&raw)?)),
             Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(None),
@@ -103,21 +96,21 @@ impl OscalControlsProvider {
         }
     }
 
-    /// Load the catalog for a framework: fetch fresh + snapshot the exact bytes;
-    /// on network failure, fall back to the last snapshot so scans still run.
-    pub async fn load(&self, framework: ComplianceFramework) -> Result<OscalDocument, CoreError> {
+    /// Load the catalog for a framework token: fetch fresh + snapshot the exact
+    /// bytes; on network failure, fall back to the last snapshot so scans run.
+    async fn load_token(&self, framework: &str) -> Result<OscalDocument, CoreError> {
         match self.fetch_raw(framework).await {
             Ok(raw) => {
                 let doc: OscalDocument = serde_json::from_slice(&raw)?;
                 if let Err(e) = self.write_snapshot(framework, &raw).await {
-                    tracing::warn!(%framework, error = %e, "failed to write OSCAL snapshot");
+                    tracing::warn!(framework, error = %e, "failed to write OSCAL snapshot");
                 }
                 Ok(doc)
             }
             Err(fetch_err) => match self.read_snapshot(framework).await? {
                 Some(doc) => {
                     tracing::warn!(
-                        %framework, error = %fetch_err,
+                        framework, error = %fetch_err,
                         "OSCAL catalog fetch failed; falling back to snapshot"
                     );
                     Ok(doc)
@@ -126,6 +119,17 @@ impl OscalControlsProvider {
             },
         }
     }
+
+    /// Load the OSCAL catalog for a compliance framework.
+    pub async fn load(&self, framework: ComplianceFramework) -> Result<OscalDocument, CoreError> {
+        self.load_token(&framework.to_string()).await
+    }
+
+    /// Load the code-checkable master-controls catalog
+    /// (`?framework=master-controls`).
+    pub async fn load_master_controls(&self) -> Result<OscalDocument, CoreError> {
+        self.load_token("master-controls").await
+    }
 }
 
 /// Order controls whose title/text mention the query context first (stable), then
@@ -181,11 +185,11 @@ mod tests {
     fn builds_catalog_url_and_snapshot_path() {
         let p = provider(std::path::Path::new("/snap"));
         assert_eq!(
-            p.catalog_url(ComplianceFramework::Cra),
+            p.catalog_url("cra"),
             "http://unused/api/compliance/v1/oscal/catalog?framework=cra"
         );
         assert_eq!(
-            p.snapshot_path(ComplianceFramework::Cra),
+            p.snapshot_path("cra"),
             std::path::Path::new("/snap/oscal-catalog-cra.json")
         );
     }
@@ -213,19 +217,11 @@ mod tests {
     async fn snapshot_round_trip_and_offline_fallback() {
         let dir = std::env::temp_dir().join(format!("oscal-test-{}", uuid::Uuid::new_v4()));
         let p = provider(&dir);
-        assert!(p
-            .read_snapshot(ComplianceFramework::Cra)
-            .await
-            .unwrap()
-            .is_none());
-        p.write_snapshot(ComplianceFramework::Cra, MINI_CATALOG.as_bytes())
+        assert!(p.read_snapshot("cra").await.unwrap().is_none());
+        p.write_snapshot("cra", MINI_CATALOG.as_bytes())
             .await
             .unwrap();
-        let doc = p
-            .read_snapshot(ComplianceFramework::Cra)
-            .await
-            .unwrap()
-            .unwrap();
+        let doc = p.read_snapshot("cra").await.unwrap().unwrap();
         assert_eq!(doc.to_controls().len(), 1);
         assert_eq!(doc.framework(), Some(ComplianceFramework::Cra));
         let _ = std::fs::remove_dir_all(&dir);
diff --git a/compliance-agent/src/controls/scan_triage.rs b/compliance-agent/src/controls/scan_triage.rs
index 6c8b5d9..3c7e62c 100644
--- a/compliance-agent/src/controls/scan_triage.rs
+++ b/compliance-agent/src/controls/scan_triage.rs
@@ -16,9 +16,15 @@ use compliance_core::models::onboarding::ComplianceFramework;
 use compliance_core::AgentConfig;
 use control_map::ControlMap;
 
-use super::{ControlTriage, LlmControlJudge, OscalControlsProvider, TriageOutcome};
+use super::{
+    ControlIndex, ControlTriage, LlmControlJudge, OscalControlsProvider, SemanticControlChecker,
+    TriageOutcome,
+};
 use crate::llm::LlmClient;
 
+/// Nearest master controls judged per code region in the semantic pass.
+const SEMANTIC_TOP_K: usize = 5;
+
 /// Lines of context to read on each side of a finding's line.
 const REGION_WINDOW: usize = 6;
 
@@ -116,6 +122,103 @@ fn fetch_region(repo_path: &Path, file: &str, line: u32) -> Option<CandidateRegi
     })
 }
 
+/// Master-controls **semantic** pass: for each finding's code region, retrieve the
+/// top-K nearest master controls by embedding, have the grounded judge confirm,
+/// and stamp the confirmed control ids onto the finding — the scale path for the
+/// ~13.6k master-control corpus (which has no CWE to LUT on). Returns the number
+/// of findings that gained a master-control ref.
+///
+/// Opt-in: the orchestrator does not run this yet. It builds the control embedding
+/// index per call (embeds the whole corpus) — production should cache/persist that
+/// index rather than rebuild it each scan.
+pub async fn semantic_stamp_findings(
+    config: &AgentConfig,
+    llm: Arc<LlmClient>,
+    repo_path: &Path,
+    findings: &mut [Finding],
+) -> usize {
+    let Some(base_url) = config.breakpilot.base_url.clone() else {
+        return 0;
+    };
+    let provider = OscalControlsProvider::new(
+        reqwest::Client::new(),
+        base_url,
+        config.breakpilot.token.clone(),
+        &config.breakpilot.snapshot_dir,
+    );
+    let doc = match provider.load_master_controls().await {
+        Ok(d) => d,
+        Err(e) => {
+            tracing::warn!(error = %e, "master-controls catalog unavailable; skipping semantic pass");
+            return 0;
+        }
+    };
+    let specs: Vec<ControlCheckSpec> = doc
+        .to_controls()
+        .into_iter()
+        .map(|c| ControlCheckSpec {
+            control_id: c.id,
+            title: c.title,
+            requirement: c.text,
+            default_cwe: None,
+            severity: Severity::Medium,
+        })
+        .collect();
+    let index = match ControlIndex::build(&llm, specs).await {
+        Ok(i) if !i.is_empty() => i,
+        Ok(_) => return 0,
+        Err(e) => {
+            tracing::warn!(error = %e, "failed to embed master-controls corpus");
+            return 0;
+        }
+    };
+    let checker = SemanticControlChecker::new(LlmControlJudge::new(llm.clone()));
+
+    let mut tagged = 0;
+    for finding in findings.iter_mut() {
+        if finding.status == FindingStatus::FalsePositive {
+            continue;
+        }
+        let (Some(file), Some(line)) = (finding.file_path.clone(), finding.line_number) else {
+            continue;
+        };
+        let Some(region) = fetch_region(repo_path, &file, line) else {
+            continue;
+        };
+        let region_emb = match llm.embed(vec![region.content.clone()]).await {
+            Ok(mut embs) => match embs.pop() {
+                Some(v) => v,
+                None => continue,
+            },
+            Err(e) => {
+                tracing::warn!(error = %e, "region embed failed; skipping finding");
+                continue;
+            }
+        };
+        let confirmed = checker
+            .check(
+                &index,
+                &region,
+                &region_emb,
+                SEMANTIC_TOP_K,
+                &finding.repo_id,
+            )
+            .await;
+        let before = finding.control_refs.len();
+        for f in confirmed {
+            for cref in f.control_refs {
+                if !finding.control_refs.contains(&cref) {
+                    finding.control_refs.push(cref);
+                }
+            }
+        }
+        if finding.control_refs.len() > before {
+            tagged += 1;
+        }
+    }
+    tagged
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/compliance-agent/src/controls/semantic.rs b/compliance-agent/src/controls/semantic.rs
new file mode 100644
index 0000000..1584de7
--- /dev/null
+++ b/compliance-agent/src/controls/semantic.rs
@@ -0,0 +1,119 @@
+//! Semantic control mapping: retrieve the top-K controls nearest a code region,
+//! then confirm each with the grounded judge.
+//!
+//! The `region → controls` direction (vs. the CWE-LUT's `finding → control`) is
+//! what scales to the full master-control corpus: the LLM only ever judges a
+//! handful of retrieved candidates, and every surviving verdict is still anchored
+//! to real code by the grounding gate.
+
+use compliance_core::control_check::{ground, CandidateRegion};
+use compliance_core::models::Finding;
+
+use super::index::ControlIndex;
+use super::judge::ControlJudge;
+
+/// Retrieve → judge → ground, generic over the judge so tests use a stub.
+pub struct SemanticControlChecker<J> {
+    judge: J,
+}
+
+impl<J: ControlJudge> SemanticControlChecker<J> {
+    pub fn new(judge: J) -> Self {
+        Self { judge }
+    }
+
+    /// Map a code region to the controls it violates. `region_embedding` is the
+    /// region's embedding (the caller computes it via the LLM); the top-`k`
+    /// nearest controls in `index` are judged and grounded.
+    pub async fn check(
+        &self,
+        index: &ControlIndex,
+        region: &CandidateRegion,
+        region_embedding: &[f64],
+        k: usize,
+        repo_id: &str,
+    ) -> Vec<Finding> {
+        let candidates = index.nearest(region_embedding, k);
+        let mut findings = Vec::new();
+        for spec in &candidates {
+            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::{ControlCheckSpec, LlmVerdict};
+    use compliance_core::models::finding::Severity;
+
+    struct StubJudge {
+        verdict: LlmVerdict,
+    }
+    impl ControlJudge for StubJudge {
+        async fn judge(&self, _s: &ControlCheckSpec, _r: &CandidateRegion) -> LlmVerdict {
+            self.verdict.clone()
+        }
+    }
+
+    fn spec(id: &str) -> ControlCheckSpec {
+        ControlCheckSpec {
+            control_id: id.into(),
+            title: id.into(),
+            requirement: id.into(),
+            default_cwe: None,
+            severity: Severity::Medium,
+        }
+    }
+
+    #[tokio::test]
+    async fn retrieves_then_grounds_the_nearest_control() {
+        let index = ControlIndex::from_embeddings(vec![
+            (spec("mc-near"), vec![1.0, 0.0]),
+            (spec("mc-far"), vec![0.0, 1.0]),
+        ]);
+        let checker = SemanticControlChecker::new(StubJudge {
+            verdict: LlmVerdict {
+                violates: true,
+                snippet: "PASSWORD = \"admin\"".into(),
+                cwe: None,
+                confidence: 0.9,
+            },
+        });
+        let region = CandidateRegion {
+            file: "src/auth.py".into(),
+            start_line: 1,
+            content: "PASSWORD = \"admin\"\n".into(),
+        };
+        // Query embedding nearest to mc-near; k=1 → only mc-near is judged.
+        let findings = checker
+            .check(&index, &region, &[0.95, 0.05], 1, "repo")
+            .await;
+        assert_eq!(findings.len(), 1);
+        assert_eq!(findings[0].control_refs, vec!["mc-near".to_string()]);
+    }
+
+    #[tokio::test]
+    async fn ungrounded_verdict_is_dropped() {
+        let index = ControlIndex::from_embeddings(vec![(spec("mc-near"), vec![1.0, 0.0])]);
+        let checker = SemanticControlChecker::new(StubJudge {
+            verdict: LlmVerdict {
+                violates: true,
+                snippet: "not in the region".into(),
+                cwe: None,
+                confidence: 0.9,
+            },
+        });
+        let region = CandidateRegion {
+            file: "f".into(),
+            start_line: 1,
+            content: "real code\n".into(),
+        };
+        let findings = checker.check(&index, &region, &[1.0, 0.0], 1, "repo").await;
+        assert!(findings.is_empty());
+    }
+}