diff --git a/gitnexus/src/core/ingestion/mro-processor.ts b/gitnexus/src/core/ingestion/mro-processor.ts
index 10c915c32..fa5816eb5 100644
--- a/gitnexus/src/core/ingestion/mro-processor.ts
+++ b/gitnexus/src/core/ingestion/mro-processor.ts
@@ -441,10 +441,23 @@ export function computeMRO(graph: KnowledgeGraph): MROResult {
 
 /**
  * Check if two parameter type arrays match.
- * Lenient: if either side has no type info, match by name only.
+ * When either side has no type info, fall back to parameterCount comparison
+ * (arity-compatible matching). If both have parameterCount and they differ,
+ * return false. If counts match or either is undefined, return true (lenient).
  */
-function parameterTypesMatch(a: string[], b: string[]): boolean {
-  if (a.length === 0 || b.length === 0) return true;
+function parameterTypesMatch(
+  a: string[],
+  b: string[],
+  aParamCount?: number,
+  bParamCount?: number,
+): boolean {
+  if (a.length === 0 || b.length === 0) {
+    // Fall back to arity check when type info is missing
+    if (aParamCount !== undefined && bParamCount !== undefined) {
+      return aParamCount === bParamCount;
+    }
+    return true; // lenient when either count is unknown
+  }
   if (a.length !== b.length) return false;
   return a.every((t, i) => t === b[i]);
 }
@@ -468,24 +481,24 @@ function emitMethodImplementsEdges(
 
     // Get this class's own methods
     const ownMethodIds = methodMap.get(classId) ?? [];
-    if (ownMethodIds.length === 0) continue;
 
-    // Build a lookup: methodName → Array<{methodId, parameterTypes}> for own methods
+    // Build a lookup: methodName → Array<{methodId, parameterTypes, parameterCount}> for own methods
     const ownMethodsByName = new Map<
       string,
-      Array<{ methodId: string; parameterTypes: string[] }>
+      Array<{ methodId: string; parameterTypes: string[]; parameterCount?: number }>
     >();
     for (const methodId of ownMethodIds) {
       const methodNode = graph.getNode(methodId);
       if (!methodNode || methodNode.label === 'Property') continue;
       const name = methodNode.properties.name as string;
       const parameterTypes = (methodNode.properties.parameterTypes as string[] | undefined) ?? [];
+      const parameterCount = methodNode.properties.parameterCount as number | undefined;
       let bucket = ownMethodsByName.get(name);
       if (!bucket) {
         bucket = [];
         ownMethodsByName.set(name, bucket);
       }
-      bucket.push({ methodId, parameterTypes });
+      bucket.push({ methodId, parameterTypes, parameterCount });
     }
 
     // Collect ALL transitive ancestors and classify each as EXTENDS or IMPLEMENTS
@@ -514,29 +527,72 @@ function emitMethodImplementsEdges(
         const ancestorName = ancestorMethodNode.properties.name as string;
         const ancestorParamTypes =
           (ancestorMethodNode.properties.parameterTypes as string[] | undefined) ?? [];
+        const ancestorParamCount = ancestorMethodNode.properties.parameterCount as
+          | number
+          | undefined;
 
-        // Find matching method in own class by name + parameterTypes
+        // Find matching method in own class by name + parameterTypes/arity
         const candidates = ownMethodsByName.get(ancestorName);
-        if (!candidates) continue;
 
-        for (const candidate of candidates) {
-          if (parameterTypesMatch(candidate.parameterTypes, ancestorParamTypes)) {
-            const edgeKey = `${candidate.methodId}->${ancestorMethodId}`;
-            if (emitted.has(edgeKey)) break;
-            emitted.add(edgeKey);
-
-            graph.addRelationship({
-              id: generateId('METHOD_IMPLEMENTS', edgeKey),
-              sourceId: candidate.methodId,
-              targetId: ancestorMethodId,
-              type: 'METHOD_IMPLEMENTS',
-              confidence: 1.0,
-              reason: '',
-            });
-            edgeCount++;
-            break; // first match wins for this ancestor method
+        // Unit 3: If no own method matches, walk the EXTENDS chain to find inherited concrete method
+        if (!candidates || candidates.length === 0) {
+          const inherited = findInheritedMethod(
+            classId,
+            ancestorName,
+            ancestorParamTypes,
+            ancestorParamCount,
+            graph,
+            parentMap,
+            methodMap,
+            parentEdgeType,
+          );
+          if (inherited) {
+            const edgeKey = `${inherited.methodId}->${ancestorMethodId}`;
+            if (!emitted.has(edgeKey)) {
+              emitted.add(edgeKey);
+              graph.addRelationship({
+                id: generateId('METHOD_IMPLEMENTS', edgeKey),
+                sourceId: inherited.methodId,
+                targetId: ancestorMethodId,
+                type: 'METHOD_IMPLEMENTS',
+                confidence: 1.0,
+                reason: '',
+              });
+              edgeCount++;
+            }
           }
+          continue;
         }
+
+        // Unit 4: Filter candidates by type/arity match, then check for ambiguity
+        const matching = candidates.filter((c) =>
+          parameterTypesMatch(
+            c.parameterTypes,
+            ancestorParamTypes,
+            c.parameterCount,
+            ancestorParamCount,
+          ),
+        );
+
+        if (matching.length === 0) continue;
+
+        // If multiple candidates match at name+arity level, emit no edge (ambiguous)
+        if (matching.length > 1) continue;
+
+        const winner = matching[0];
+        const edgeKey = `${winner.methodId}->${ancestorMethodId}`;
+        if (emitted.has(edgeKey)) continue;
+        emitted.add(edgeKey);
+
+        graph.addRelationship({
+          id: generateId('METHOD_IMPLEMENTS', edgeKey),
+          sourceId: winner.methodId,
+          targetId: ancestorMethodId,
+          type: 'METHOD_IMPLEMENTS',
+          confidence: 1.0,
+          reason: '',
+        });
+        edgeCount++;
       }
     }
   }
@@ -544,6 +600,75 @@ function emitMethodImplementsEdges(
   return edgeCount;
 }
 
+/**
+ * Walk the class's EXTENDS chain (not IMPLEMENTS) to find the nearest
+ * concrete method matching the given name and parameter signature.
+ * Returns the first matching method found in BFS order, or null.
+ */
+function findInheritedMethod(
+  classId: string,
+  methodName: string,
+  targetParamTypes: string[],
+  targetParamCount: number | undefined,
+  graph: KnowledgeGraph,
+  parentMap: Map<string, string[]>,
+  methodMap: Map<string, string[]>,
+  parentEdgeType: Map<string, Map<string, 'EXTENDS' | 'IMPLEMENTS'>>,
+): { methodId: string; parameterTypes: string[] } | null {
+  const visited = new Set<string>();
+  const queue: string[] = [];
+
+  // Seed with direct EXTENDS parents only
+  const directParents = parentMap.get(classId) ?? [];
+  const directEdges = parentEdgeType.get(classId);
+  for (const pid of directParents) {
+    const et = directEdges?.get(pid);
+    if (et === 'EXTENDS') {
+      // Also check that the parent is not an Interface/Trait
+      const parentNode = graph.getNode(pid);
+      if (parentNode && parentNode.label !== 'Interface' && parentNode.label !== 'Trait') {
+        queue.push(pid);
+      }
+    }
+  }
+
+  while (queue.length > 0) {
+    const ancestorId = queue.shift()!;
+    if (visited.has(ancestorId)) continue;
+    visited.add(ancestorId);
+
+    // Check this ancestor's methods
+    const methods = methodMap.get(ancestorId) ?? [];
+    for (const mid of methods) {
+      const mNode = graph.getNode(mid);
+      if (!mNode || mNode.label === 'Property') continue;
+      if (mNode.properties.name !== methodName) continue;
+
+      const mParamTypes = (mNode.properties.parameterTypes as string[] | undefined) ?? [];
+      const mParamCount = mNode.properties.parameterCount as number | undefined;
+      if (parameterTypesMatch(mParamTypes, targetParamTypes, mParamCount, targetParamCount)) {
+        return { methodId: mid, parameterTypes: mParamTypes };
+      }
+    }
+
+    // Continue walking EXTENDS parents of this ancestor
+    const grandparents = parentMap.get(ancestorId) ?? [];
+    const ancestorEdges = parentEdgeType.get(ancestorId);
+    for (const gp of grandparents) {
+      if (visited.has(gp)) continue;
+      const gpEdge = ancestorEdges?.get(gp);
+      if (gpEdge === 'EXTENDS') {
+        const gpNode = graph.getNode(gp);
+        if (gpNode && gpNode.label !== 'Interface' && gpNode.label !== 'Trait') {
+          queue.push(gp);
+        }
+      }
+    }
+  }
+
+  return null;
+}
+
 /**
  * Build transitive edge types for a class using BFS from the class to all ancestors.
  *
diff --git a/gitnexus/src/mcp/local/local-backend.ts b/gitnexus/src/mcp/local/local-backend.ts
index 1d54cbb21..af129e2f8 100644
--- a/gitnexus/src/mcp/local/local-backend.ts
+++ b/gitnexus/src/mcp/local/local-backend.ts
@@ -97,6 +97,7 @@ export const VALID_RELATION_TYPES = new Set([
   'HAS_METHOD',
   'HAS_PROPERTY',
   'METHOD_OVERRIDES',
+  'OVERRIDES', // Legacy alias — dual-read for pre-rename indexes
   'METHOD_IMPLEMENTS',
   'ACCESSES',
   'HANDLES_ROUTE',
@@ -177,7 +178,6 @@ export class LocalBackend {
   private repos: Map<string, RepoHandle> = new Map();
   private contextCache: Map<string, CodebaseContext> = new Map();
   private initializedRepos: Set<string> = new Set();
-  private migratedRepos: Set<string> = new Set();
   private reinitPromises: Map<string, Promise<void>> = new Map();
   private lastStalenessCheck: Map<string, number> = new Map();
   private groupToolSvc: GroupService | null = null;
@@ -410,20 +410,6 @@ export class LocalBackend {
     try {
       await initLbug(repoId, handle.lbugPath);
       this.initializedRepos.add(repoId);
-      // Migrate legacy OVERRIDES → METHOD_OVERRIDES (once per session per repo)
-      // TODO: remove this migration after a few releases once most users have migrated indexes
-      if (!this.migratedRepos.has(repoId)) {
-        this.migratedRepos.add(repoId);
-        try {
-          await executeParameterized(
-            repoId,
-            `MATCH ()-[r:CodeRelation {type: 'OVERRIDES'}]->() SET r.type = 'METHOD_OVERRIDES'`,
-            {},
-          );
-        } catch {
-          /* Old index may not have OVERRIDES edges — ignore */
-        }
-      }
     } catch (err: any) {
       // If lock error, mark as not initialized so next call retries
       this.initializedRepos.delete(repoId);
@@ -1218,7 +1204,7 @@ export class LocalBackend {
       repo.id,
       `
       MATCH (caller)-[r:CodeRelation]->(n {id: $symId})
-      WHERE r.type IN ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'HAS_METHOD', 'HAS_PROPERTY', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS', 'ACCESSES']
+      WHERE r.type IN ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'HAS_METHOD', 'HAS_PROPERTY', 'METHOD_OVERRIDES', 'OVERRIDES', 'METHOD_IMPLEMENTS', 'ACCESSES']
       RETURN r.type AS relType, caller.id AS uid, caller.name AS name, caller.filePath AS filePath, labels(caller)[0] AS kind
       LIMIT 30
     `,
@@ -1308,7 +1294,7 @@ export class LocalBackend {
       repo.id,
       `
       MATCH (n {id: $symId})-[r:CodeRelation]->(target)
-      WHERE r.type IN ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'HAS_METHOD', 'HAS_PROPERTY', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS', 'ACCESSES']
+      WHERE r.type IN ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'HAS_METHOD', 'HAS_PROPERTY', 'METHOD_OVERRIDES', 'OVERRIDES', 'METHOD_IMPLEMENTS', 'ACCESSES']
       RETURN r.type AS relType, target.id AS uid, target.name AS name, target.filePath AS filePath, labels(target)[0] AS kind
       LIMIT 30
     `,
@@ -1934,9 +1920,11 @@ export class LocalBackend {
     const rawRelTypes =
       mappedRelTypes && mappedRelTypes.length > 0
         ? mappedRelTypes.filter((t: string) => VALID_RELATION_TYPES.has(t))
-        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS'];
+        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS'];
     const relationTypes =
-      rawRelTypes.length > 0 ? rawRelTypes : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS'];
+      rawRelTypes.length > 0
+        ? rawRelTypes
+        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS'];
     const includeTests = params.includeTests ?? false;
     const minConfidence = params.minConfidence ?? 0;
 
@@ -2486,9 +2474,11 @@ export class LocalBackend {
     const rawRelTypes =
       mappedRelTypes && mappedRelTypes.length > 0
         ? mappedRelTypes.filter((t: string) => VALID_RELATION_TYPES.has(t))
-        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS'];
+        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS'];
     const relationTypes =
-      rawRelTypes.length > 0 ? rawRelTypes : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS'];
+      rawRelTypes.length > 0
+        ? rawRelTypes
+        : ['CALLS', 'IMPORTS', 'EXTENDS', 'IMPLEMENTS', 'METHOD_OVERRIDES', 'METHOD_IMPLEMENTS'];
 
     try {
       return await this._runImpactBFS(repo, sym, symType, dir, {
diff --git a/gitnexus/test/unit/mro-processor.test.ts b/gitnexus/test/unit/mro-processor.test.ts
index 9be1a9566..dcc8f821e 100644
--- a/gitnexus/test/unit/mro-processor.test.ts
+++ b/gitnexus/test/unit/mro-processor.test.ts
@@ -867,5 +867,227 @@ describe('computeMRO', () => {
       });
       expect(implementingMethods).toContain(concreteId);
     });
+
+    describe('METHOD_IMPLEMENTS inherited + arity matching', () => {
+      it('inherited implementation: Base.foo satisfies I.foo when C has no own foo', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'Base', 'java');
+        addClass(graph, 'I', 'java', 'Interface');
+        addClass(graph, 'C', 'java');
+
+        addExtends(graph, 'C', 'Base');
+        addImplements(graph, 'C', 'I');
+
+        const baseFoo = addMethod(graph, 'Base', 'foo');
+        const iFoo = addMethod(graph, 'I', 'foo', 'Interface');
+
+        const result = computeMRO(graph);
+
+        const edges: any[] = [];
+        graph.forEachRelationship((rel) => {
+          if (rel.type === 'METHOD_IMPLEMENTS') edges.push(rel);
+        });
+
+        expect(edges).toHaveLength(1);
+        expect(edges[0].sourceId).toBe(baseFoo);
+        expect(edges[0].targetId).toBe(iFoo);
+        expect(result.methodImplementsEdges).toBe(1);
+      });
+
+      it('class has own method — no inherited lookup needed', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'Base2', 'java');
+        addClass(graph, 'I2', 'java', 'Interface');
+        addClass(graph, 'C2', 'java');
+
+        addExtends(graph, 'C2', 'Base2');
+        addImplements(graph, 'C2', 'I2');
+
+        const baseFoo = addMethod(graph, 'Base2', 'foo');
+        const iFoo = addMethod(graph, 'I2', 'foo', 'Interface');
+        const cFoo = addMethod(graph, 'C2', 'foo');
+
+        const result = computeMRO(graph);
+
+        const edges: any[] = [];
+        graph.forEachRelationship((rel) => {
+          if (rel.type === 'METHOD_IMPLEMENTS') edges.push(rel);
+        });
+
+        // Should use C2.foo, not Base2.foo
+        expect(edges).toHaveLength(1);
+        expect(edges[0].sourceId).toBe(cFoo);
+        expect(edges[0].targetId).toBe(iFoo);
+      });
+
+      it('deep inheritance chain: GrandBase.foo satisfies I.foo', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'GrandBase', 'java');
+        addClass(graph, 'Base3', 'java');
+        addClass(graph, 'I3', 'java', 'Interface');
+        addClass(graph, 'C3', 'java');
+
+        addExtends(graph, 'Base3', 'GrandBase');
+        addExtends(graph, 'C3', 'Base3');
+        addImplements(graph, 'C3', 'I3');
+
+        const grandFoo = addMethod(graph, 'GrandBase', 'foo');
+        // Base3 has NO foo
+        const iFoo = addMethod(graph, 'I3', 'foo', 'Interface');
+
+        const result = computeMRO(graph);
+
+        const edges: any[] = [];
+        graph.forEachRelationship((rel) => {
+          if (rel.type === 'METHOD_IMPLEMENTS') edges.push(rel);
+        });
+
+        expect(edges).toHaveLength(1);
+        expect(edges[0].sourceId).toBe(grandFoo);
+        expect(edges[0].targetId).toBe(iFoo);
+        expect(result.methodImplementsEdges).toBe(1);
+      });
+
+      it('arity mismatch prevents false match', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'IArity', 'java', 'Interface');
+        addClass(graph, 'CArity', 'java');
+        addImplements(graph, 'CArity', 'IArity');
+
+        // Interface method: parameterCount=2, no parameterTypes
+        const iMethodId = generateId('Method', 'IArity.process');
+        graph.addNode({
+          id: iMethodId,
+          label: 'Method',
+          properties: { name: 'process', filePath: 'src/IArity.ts', parameterCount: 2 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Interface', 'IArity')}->${iMethodId}`),
+          sourceId: generateId('Interface', 'IArity'),
+          targetId: iMethodId,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        // Class method: parameterCount=3, no parameterTypes
+        const cMethodId = generateId('Method', 'CArity.process');
+        graph.addNode({
+          id: cMethodId,
+          label: 'Method',
+          properties: { name: 'process', filePath: 'src/CArity.ts', parameterCount: 3 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Class', 'CArity')}->${cMethodId}`),
+          sourceId: generateId('Class', 'CArity'),
+          targetId: cMethodId,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        const result = computeMRO(graph);
+        expect(result.methodImplementsEdges).toBe(0);
+      });
+
+      it('arity match when types missing', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'IArityOk', 'java', 'Interface');
+        addClass(graph, 'CArityOk', 'java');
+        addImplements(graph, 'CArityOk', 'IArityOk');
+
+        // Interface method: parameterCount=2, no parameterTypes
+        const iMethodId = generateId('Method', 'IArityOk.process');
+        graph.addNode({
+          id: iMethodId,
+          label: 'Method',
+          properties: { name: 'process', filePath: 'src/IArityOk.ts', parameterCount: 2 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Interface', 'IArityOk')}->${iMethodId}`),
+          sourceId: generateId('Interface', 'IArityOk'),
+          targetId: iMethodId,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        // Class method: parameterCount=2, no parameterTypes
+        const cMethodId = generateId('Method', 'CArityOk.process');
+        graph.addNode({
+          id: cMethodId,
+          label: 'Method',
+          properties: { name: 'process', filePath: 'src/CArityOk.ts', parameterCount: 2 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Class', 'CArityOk')}->${cMethodId}`),
+          sourceId: generateId('Class', 'CArityOk'),
+          targetId: cMethodId,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        const result = computeMRO(graph);
+        expect(result.methodImplementsEdges).toBe(1);
+      });
+
+      it('multiple same-arity candidates = ambiguous, no edge emitted', () => {
+        const graph = createKnowledgeGraph();
+        addClass(graph, 'IAmbig', 'java', 'Interface');
+        addClass(graph, 'CAmbig', 'java');
+        addImplements(graph, 'CAmbig', 'IAmbig');
+
+        // Interface method: parameterCount=1, no parameterTypes
+        const iMethodId = generateId('Method', 'IAmbig.handle');
+        graph.addNode({
+          id: iMethodId,
+          label: 'Method',
+          properties: { name: 'handle', filePath: 'src/IAmbig.ts', parameterCount: 1 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Interface', 'IAmbig')}->${iMethodId}`),
+          sourceId: generateId('Interface', 'IAmbig'),
+          targetId: iMethodId,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        // Two class methods named handle, both with parameterCount=1
+        const cMethod1 = generateId('Method', 'CAmbig.handle.1');
+        graph.addNode({
+          id: cMethod1,
+          label: 'Method',
+          properties: { name: 'handle', filePath: 'src/CAmbig.ts', parameterCount: 1 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Class', 'CAmbig')}->${cMethod1}`),
+          sourceId: generateId('Class', 'CAmbig'),
+          targetId: cMethod1,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        const cMethod2 = generateId('Method', 'CAmbig.handle.2');
+        graph.addNode({
+          id: cMethod2,
+          label: 'Method',
+          properties: { name: 'handle', filePath: 'src/CAmbig.ts', parameterCount: 1 },
+        });
+        graph.addRelationship({
+          id: generateId('HAS_METHOD', `${generateId('Class', 'CAmbig')}->${cMethod2}`),
+          sourceId: generateId('Class', 'CAmbig'),
+          targetId: cMethod2,
+          type: 'HAS_METHOD',
+          confidence: 1.0,
+          reason: '',
+        });
+
+        const result = computeMRO(graph);
+        expect(result.methodImplementsEdges).toBe(0);
+      });
+    });
   });
 });
diff --git a/gitnexus/test/unit/security.test.ts b/gitnexus/test/unit/security.test.ts
index ac6cb8d0e..0adee1915 100644
--- a/gitnexus/test/unit/security.test.ts
+++ b/gitnexus/test/unit/security.test.ts
@@ -106,7 +106,7 @@ describe('isWriteQuery', () => {
 
 describe('VALID_RELATION_TYPES', () => {
   it('contains all expected relation types', () => {
-    expect(VALID_RELATION_TYPES.size).toBe(14);
+    expect(VALID_RELATION_TYPES.size).toBe(15);
     for (const t of [
       'CALLS',
       'IMPORTS',
@@ -115,6 +115,7 @@ describe('VALID_RELATION_TYPES', () => {
       'HAS_METHOD',
       'HAS_PROPERTY',
       'METHOD_OVERRIDES',
+      'OVERRIDES',
       'METHOD_IMPLEMENTS',
       'ACCESSES',
       'HANDLES_ROUTE',