diff --git a/gitnexus/src/core/graph/graph.ts b/gitnexus/src/core/graph/graph.ts
index a3d1df713..2f49e9f4a 100644
--- a/gitnexus/src/core/graph/graph.ts
+++ b/gitnexus/src/core/graph/graph.ts
@@ -1,9 +1,21 @@
-import type { GraphNode, GraphRelationship } from 'gitnexus-shared';
+import type { GraphNode, GraphRelationship, RelationshipType } from 'gitnexus-shared';
 import { KnowledgeGraph } from './types.js';
 
+/** Fresh empty iterator per call — `[].values()` returns a new
+ *  exhausted iterator each invocation, so empty-type lookups don't
+ *  share a single already-exhausted iterator across callers. */
+function emptyRelIter(): IterableIterator<GraphRelationship> {
+  return ([] as GraphRelationship[]).values();
+}
+
 export const createKnowledgeGraph = (): KnowledgeGraph => {
   const nodeMap = new Map<string, GraphNode>();
   const relationshipMap = new Map<string, GraphRelationship>();
+  // Per-type index maintained alongside `relationshipMap`. Bucket
+  // values are `Map<id, Relationship>` so per-type iteration is cheap
+  // and per-edge removal is O(1). See plan
+  // docs/plans/2026-04-20-002-perf-parse-heritage-mro-plan.md (Unit 1).
+  const relationshipsByType = new Map<RelationshipType, Map<string, GraphRelationship>>();
 
   const addNode = (node: GraphNode) => {
     if (!nodeMap.has(node.id)) {
@@ -12,9 +24,14 @@ export const createKnowledgeGraph = (): KnowledgeGraph => {
   };
 
   const addRelationship = (relationship: GraphRelationship) => {
-    if (!relationshipMap.has(relationship.id)) {
-      relationshipMap.set(relationship.id, relationship);
+    if (relationshipMap.has(relationship.id)) return;
+    relationshipMap.set(relationship.id, relationship);
+    let bucket = relationshipsByType.get(relationship.type);
+    if (bucket === undefined) {
+      bucket = new Map();
+      relationshipsByType.set(relationship.type, bucket);
     }
+    bucket.set(relationship.id, relationship);
   };
 
   /**
@@ -25,10 +42,12 @@ export const createKnowledgeGraph = (): KnowledgeGraph => {
 
     nodeMap.delete(nodeId);
 
-    // Remove all relationships involving this node
+    // Remove all relationships involving this node — clean up both
+    // indexes in lockstep so the per-type buckets never drift.
     for (const [relId, rel] of relationshipMap) {
       if (rel.sourceId === nodeId || rel.targetId === nodeId) {
         relationshipMap.delete(relId);
+        relationshipsByType.get(rel.type)?.delete(relId);
       }
     }
     return true;
@@ -39,7 +58,11 @@ export const createKnowledgeGraph = (): KnowledgeGraph => {
    * Returns true if the relationship existed and was removed, false otherwise.
    */
   const removeRelationship = (relationshipId: string): boolean => {
-    return relationshipMap.delete(relationshipId);
+    const rel = relationshipMap.get(relationshipId);
+    if (rel === undefined) return false;
+    relationshipMap.delete(relationshipId);
+    relationshipsByType.get(rel.type)?.delete(relationshipId);
+    return true;
   };
 
   /**
@@ -67,6 +90,10 @@ export const createKnowledgeGraph = (): KnowledgeGraph => {
 
     iterNodes: () => nodeMap.values(),
     iterRelationships: () => relationshipMap.values(),
+    iterRelationshipsByType: (type: RelationshipType) => {
+      const bucket = relationshipsByType.get(type);
+      return bucket === undefined ? emptyRelIter() : bucket.values();
+    },
     forEachNode(fn: (node: GraphNode) => void) {
       nodeMap.forEach(fn);
     },
diff --git a/gitnexus/src/core/graph/types.ts b/gitnexus/src/core/graph/types.ts
index a3c97942c..539f77987 100644
--- a/gitnexus/src/core/graph/types.ts
+++ b/gitnexus/src/core/graph/types.ts
@@ -6,7 +6,7 @@
  *
  * This file only defines the CLI's KnowledgeGraph with mutation methods.
  */
-import type { GraphNode, GraphRelationship } from 'gitnexus-shared';
+import type { GraphNode, GraphRelationship, RelationshipType } from 'gitnexus-shared';
 
 // CLI-specific: full KnowledgeGraph with mutation methods for incremental updates
 export interface KnowledgeGraph {
@@ -14,6 +14,17 @@ export interface KnowledgeGraph {
   relationships: GraphRelationship[];
   iterNodes: () => IterableIterator<GraphNode>;
   iterRelationships: () => IterableIterator<GraphRelationship>;
+  /**
+   * Iterate ONLY relationships of the given type, backed by a per-type
+   * index maintained in `addRelationship` / `removeRelationship` /
+   * `removeNode` / `removeNodesByFile`. Returns an empty iterator when
+   * the graph contains no relationships of that type.
+   *
+   * Prefer this over `iterRelationships()` + per-edge type filtering
+   * for hot paths (MRO setup, heritage walks). Backwards-compatible:
+   * existing `iterRelationships()` callers keep working.
+   */
+  iterRelationshipsByType: (type: RelationshipType) => IterableIterator<GraphRelationship>;
   forEachNode: (fn: (node: GraphNode) => void) => void;
   forEachRelationship: (fn: (rel: GraphRelationship) => void) => void;
   getNode: (id: string) => GraphNode | undefined;
diff --git a/gitnexus/src/core/ingestion/language-provider.ts b/gitnexus/src/core/ingestion/language-provider.ts
index 351b339a7..f449aa46b 100644
--- a/gitnexus/src/core/ingestion/language-provider.ts
+++ b/gitnexus/src/core/ingestion/language-provider.ts
@@ -329,7 +329,21 @@ interface LanguageProviderConfig {
    *
    * Default: undefined (language continues to use legacy DAG).
    */
-  readonly emitScopeCaptures?: (sourceText: string, filePath: string) => readonly CaptureMatch[];
+  readonly emitScopeCaptures?: (
+    sourceText: string,
+    filePath: string,
+    /**
+     * Optional pre-parsed tree-sitter Tree the caller has already
+     * produced (e.g. from the parse phase's AST cache). When supplied,
+     * the provider SHOULD skip its own `parser.parse(sourceText)` and
+     * run its capture query against the supplied tree directly. Typed
+     * as `unknown` here to avoid leaking the tree-sitter dependency
+     * into the provider contract — the provider casts at use site.
+     * Cache miss (parameter omitted or undefined) is always safe and
+     * MUST trigger a fresh parse.
+     */
+    cachedTree?: unknown,
+  ) => readonly CaptureMatch[];
 
   /**
    * Interpret a raw `@import.statement` capture group into a `ParsedImport`.
diff --git a/gitnexus/src/core/ingestion/languages/python/captures.ts b/gitnexus/src/core/ingestion/languages/python/captures.ts
index 814516bfc..f07befed3 100644
--- a/gitnexus/src/core/ingestion/languages/python/captures.ts
+++ b/gitnexus/src/core/ingestion/languages/python/captures.ts
@@ -23,11 +23,36 @@ import { getPythonParser, getPythonScopeQuery } from './query.js';
 import { synthesizeReceiverTypeBinding } from './receiver-binding.js';
 import { computePythonArityMetadata } from './arity-metadata.js';
 
+// Dev-mode counters for the parse-cache hit-rate. Gated by
+// `PROF_SCOPE_RESOLUTION=1` to keep the hot path branch-free in
+// production. Surfaced via `getPythonCaptureCacheStats()` so
+// benchmarks / debug scripts can verify the cache is being used.
+const PROF = process.env.PROF_SCOPE_RESOLUTION === '1';
+let CACHE_HITS = 0;
+let CACHE_MISSES = 0;
+export function getPythonCaptureCacheStats(): { hits: number; misses: number } {
+  return { hits: CACHE_HITS, misses: CACHE_MISSES };
+}
+export function resetPythonCaptureCacheStats(): void {
+  CACHE_HITS = 0;
+  CACHE_MISSES = 0;
+}
+
 export function emitPythonScopeCaptures(
   sourceText: string,
   _filePath: string,
+  cachedTree?: unknown,
 ): readonly CaptureMatch[] {
-  const tree = getPythonParser().parse(sourceText);
+  // Skip the parse when the caller (parse phase's ASTCache) already
+  // produced a Tree for this source. Cache miss = re-parse, same as
+  // before. The cachedTree parameter is typed as `unknown` at the
+  // contract layer (see `LanguageProvider.emitScopeCaptures`); cast
+  // here at the use site.
+  let tree = cachedTree as ReturnType<ReturnType<typeof getPythonParser>['parse']> | undefined;
+  if (tree === undefined) {
+    tree = getPythonParser().parse(sourceText);
+    if (PROF) CACHE_MISSES++;
+  } else if (PROF) CACHE_HITS++;
   const rawMatches = getPythonScopeQuery().matches(tree.rootNode);
 
   const out: CaptureMatch[] = [];
diff --git a/gitnexus/src/core/ingestion/mro-processor.ts b/gitnexus/src/core/ingestion/mro-processor.ts
index c48cf99f3..e41b8da6c 100644
--- a/gitnexus/src/core/ingestion/mro-processor.ts
+++ b/gitnexus/src/core/ingestion/mro-processor.ts
@@ -64,32 +64,48 @@ function buildAdjacency(graph: KnowledgeGraph) {
   // Track which edge type each parent link came from
   const parentEdgeType = new Map<string, Map<string, 'EXTENDS' | 'IMPLEMENTS'>>();
 
-  graph.forEachRelationship((rel) => {
-    if (rel.type === 'EXTENDS' || rel.type === 'IMPLEMENTS') {
-      let parents = parentMap.get(rel.sourceId);
-      if (!parents) {
-        parents = [];
-        parentMap.set(rel.sourceId, parents);
-      }
-      parents.push(rel.targetId);
-
-      let edgeTypes = parentEdgeType.get(rel.sourceId);
-      if (!edgeTypes) {
-        edgeTypes = new Map();
-        parentEdgeType.set(rel.sourceId, edgeTypes);
-      }
-      edgeTypes.set(rel.targetId, rel.type);
+  // Three typed iterations replace one full-relationship-map scan
+  // with per-edge type checks. Each consumes only the edges of the
+  // type it cares about — see plan
+  // docs/plans/2026-04-20-002-perf-parse-heritage-mro-plan.md (Unit 2).
+  for (const rel of graph.iterRelationshipsByType('EXTENDS')) {
+    let parents = parentMap.get(rel.sourceId);
+    if (!parents) {
+      parents = [];
+      parentMap.set(rel.sourceId, parents);
     }
+    parents.push(rel.targetId);
 
-    if (rel.type === 'HAS_METHOD') {
-      let methods = methodMap.get(rel.sourceId);
-      if (!methods) {
-        methods = [];
-        methodMap.set(rel.sourceId, methods);
-      }
-      methods.push(rel.targetId);
+    let edgeTypes = parentEdgeType.get(rel.sourceId);
+    if (!edgeTypes) {
+      edgeTypes = new Map();
+      parentEdgeType.set(rel.sourceId, edgeTypes);
     }
-  });
+    edgeTypes.set(rel.targetId, 'EXTENDS');
+  }
+  for (const rel of graph.iterRelationshipsByType('IMPLEMENTS')) {
+    let parents = parentMap.get(rel.sourceId);
+    if (!parents) {
+      parents = [];
+      parentMap.set(rel.sourceId, parents);
+    }
+    parents.push(rel.targetId);
+
+    let edgeTypes = parentEdgeType.get(rel.sourceId);
+    if (!edgeTypes) {
+      edgeTypes = new Map();
+      parentEdgeType.set(rel.sourceId, edgeTypes);
+    }
+    edgeTypes.set(rel.targetId, 'IMPLEMENTS');
+  }
+  for (const rel of graph.iterRelationshipsByType('HAS_METHOD')) {
+    let methods = methodMap.get(rel.sourceId);
+    if (!methods) {
+      methods = [];
+      methodMap.set(rel.sourceId, methods);
+    }
+    methods.push(rel.targetId);
+  }
 
   return { parentMap, methodMap, parentEdgeType };
 }
diff --git a/gitnexus/src/core/ingestion/parsing-processor.ts b/gitnexus/src/core/ingestion/parsing-processor.ts
index b7b143039..a7bcae406 100644
--- a/gitnexus/src/core/ingestion/parsing-processor.ts
+++ b/gitnexus/src/core/ingestion/parsing-processor.ts
@@ -318,6 +318,7 @@ const processParsingSequential = async (
   files: { path: string; content: string }[],
   symbolTable: SymbolTableWriter,
   astCache: ASTCache,
+  scopeTreeCache: ASTCache | undefined,
   onFileProgress?: FileProgressCallback,
 ) => {
   const parser = await loadParser();
@@ -380,6 +381,9 @@ const processParsingSequential = async (
     }
 
     astCache.set(file.path, tree);
+    // Mirror into the cross-phase cache when supplied. parse-impl
+    // clears `astCache` between chunks; `scopeTreeCache` survives.
+    scopeTreeCache?.set(file.path, tree);
 
     const provider = getProvider(language);
     const queryString = provider.treeSitterQueries;
@@ -699,6 +703,14 @@ export const processParsing = async (
   files: { path: string; content: string }[],
   symbolTable: SymbolTableWriter,
   astCache: ASTCache,
+  /**
+   * Persistent tree cache (separate from `astCache`, which the caller
+   * clears between chunks). Sequential parses additionally write the
+   * Tree here so cross-phase consumers (scope-resolution) can read it.
+   * Worker-mode parses skip — Trees can't cross MessageChannels.
+   * Pass `undefined` if no consumer needs cross-phase access.
+   */
+  scopeTreeCache: ASTCache | undefined,
   onFileProgress?: FileProgressCallback,
   workerPool?: WorkerPool,
 ): Promise<WorkerExtractedData | null> => {
@@ -721,6 +733,13 @@ export const processParsing = async (
   }
 
   // Fallback: sequential parsing (no pre-extracted data)
-  await processParsingSequential(graph, files, symbolTable, astCache, onFileProgress);
+  await processParsingSequential(
+    graph,
+    files,
+    symbolTable,
+    astCache,
+    scopeTreeCache,
+    onFileProgress,
+  );
   return null;
 };
diff --git a/gitnexus/src/core/ingestion/pipeline-phases/parse-impl.ts b/gitnexus/src/core/ingestion/pipeline-phases/parse-impl.ts
index f8e0d3b53..dd5cc3117 100644
--- a/gitnexus/src/core/ingestion/pipeline-phases/parse-impl.ts
+++ b/gitnexus/src/core/ingestion/pipeline-phases/parse-impl.ts
@@ -41,7 +41,7 @@ import {
   getHeritageStrategyForLanguage,
 } from '../heritage-processor.js';
 import { createResolutionContext } from '../model/resolution-context.js';
-import { createASTCache } from '../ast-cache.js';
+import { ASTCache, createASTCache } from '../ast-cache.js';
 import { type PipelineProgress, getLanguageFromFilename } from 'gitnexus-shared';
 import { readFileContents } from '../filesystem-walker.js';
 import { isLanguageAvailable } from '../../tree-sitter/parser-loader.js';
@@ -109,6 +109,13 @@ export async function runChunkedParseAndResolve(
   bindingAccumulator: BindingAccumulator;
   resolutionContext: ReturnType<typeof createResolutionContext>;
   usedWorkerPool: boolean;
+  /** AST cache populated by the sequential parse path. Empty when
+   *  every chunk ran via the worker pool (workers can't return native
+   *  tree-sitter Trees across the MessageChannel). Downstream phases
+   *  (e.g. scope-resolution) read from this to skip re-parsing the
+   *  same source. See plan
+   *  docs/plans/2026-04-20-002-perf-parse-heritage-mro-plan.md (Unit 4). */
+  astCache: ASTCache;
 }> {
   const ctx = createResolutionContext();
   const symbolTable = ctx.model.symbols;
@@ -220,9 +227,18 @@ export async function runChunkedParseAndResolve(
 
   let filesParsedSoFar = 0;
 
-  // AST cache sized for one chunk (sequential fallback uses it for import/call/heritage)
+  // Two caches with different lifetimes:
+  //   - `astCache` (chunk-local, cleared between chunks) — call /
+  //     heritage / import processors read it during parse to avoid
+  //     re-parsing within the same chunk.
+  //   - `scopeTreeCache` (total-parseable-sized, never cleared by
+  //     parse-impl) — exposed via ParseOutput so scope-resolution can
+  //     skip a second tree-sitter parse. Worker-mode parses don't
+  //     populate either; consumers fall back to a fresh parse.
+  // See plan docs/plans/2026-04-20-002-perf-parse-heritage-mro-plan.md (Unit 4).
   const maxChunkFiles = chunks.reduce((max, c) => Math.max(max, c.length), 0);
   let astCache = createASTCache(maxChunkFiles);
+  const scopeTreeCache = createASTCache(Math.max(parseableScanned.length, 1));
 
   // Build import resolution context once — suffix index, file lists, resolve cache.
   const importCtx = buildImportResolutionContext(allPaths);
@@ -267,6 +283,7 @@ export async function runChunkedParseAndResolve(
         chunkFiles,
         symbolTable,
         astCache,
+        scopeTreeCache,
         (current, _total, filePath) => {
           const globalCurrent = filesParsedSoFar + current;
           const parsingProgress = 20 + (globalCurrent / totalParseable) * 62;
@@ -595,5 +612,11 @@ export async function runChunkedParseAndResolve(
     // sequential fallback handled every chunk (either due to `skipWorkers`,
     // the file-count/byte thresholds, or a pool-creation failure).
     usedWorkerPool: workerPool !== undefined,
+    // Surface the persistent scope cache so downstream phases
+    // (scope-resolution) can skip re-parsing files that the
+    // sequential path already parsed. Survives chunk boundaries; the
+    // chunk-local `astCache` above is intentionally NOT exposed
+    // because parse-impl clears it between chunks.
+    astCache: scopeTreeCache,
   };
 }
diff --git a/gitnexus/src/core/ingestion/pipeline-phases/parse.ts b/gitnexus/src/core/ingestion/pipeline-phases/parse.ts
index 6415cb6e5..0f5314efa 100644
--- a/gitnexus/src/core/ingestion/pipeline-phases/parse.ts
+++ b/gitnexus/src/core/ingestion/pipeline-phases/parse.ts
@@ -29,6 +29,7 @@ import type {
 } from '../workers/parse-worker.js';
 import type { createResolutionContext } from '../model/resolution-context.js';
 import { runChunkedParseAndResolve } from './parse-impl.js';
+import type { ASTCache } from '../ast-cache.js';
 
 export interface ParseOutput {
   /**
@@ -63,6 +64,15 @@ export interface ParseOutput {
    * see `PipelineOptions.workerThresholdsForTest`.
    */
   readonly usedWorkerPool: boolean;
+  /**
+   * AST cache populated by the sequential parse path. Empty entries
+   * for files that ran through the worker pool (workers can't return
+   * native tree-sitter Trees across the MessageChannel). Downstream
+   * phases (scope-resolution) read from this to skip re-parsing —
+   * cache miss is safe and falls back to a fresh parse. See plan
+   * docs/plans/2026-04-20-002-perf-parse-heritage-mro-plan.md (Unit 4).
+   */
+  readonly astCache: ASTCache;
 }
 
 export const parsePhase: PipelinePhase<ParseOutput> = {
diff --git a/gitnexus/src/core/ingestion/scope-extractor-bridge.ts b/gitnexus/src/core/ingestion/scope-extractor-bridge.ts
index dfa3b9b4f..19e16e940 100644
--- a/gitnexus/src/core/ingestion/scope-extractor-bridge.ts
+++ b/gitnexus/src/core/ingestion/scope-extractor-bridge.ts
@@ -38,10 +38,11 @@ export function extractParsedFile(
   sourceText: string,
   filePath: string,
   onWarn?: ScopeBridgeWarn,
+  cachedTree?: unknown,
 ): ParsedFile | undefined {
   if (provider.emitScopeCaptures === undefined) return undefined;
   try {
-    const captures = provider.emitScopeCaptures(sourceText, filePath);
+    const captures = provider.emitScopeCaptures(sourceText, filePath, cachedTree);
     return extractScope(captures, filePath, provider);
   } catch (err) {
     const message = `scope extraction failed for ${filePath}: ${
diff --git a/gitnexus/src/core/ingestion/scope-resolution/passes/mro.ts b/gitnexus/src/core/ingestion/scope-resolution/passes/mro.ts
index fac7ad5cc..b9aa39bf9 100644
--- a/gitnexus/src/core/ingestion/scope-resolution/passes/mro.ts
+++ b/gitnexus/src/core/ingestion/scope-resolution/passes/mro.ts
@@ -41,10 +41,11 @@ export function buildMro(
   nodeLookup: GraphNodeLookup,
   linearize: LinearizeStrategy,
 ): Map<string /* DefId */, string[] /* DefId[] */> {
-  // Step 1: parentsByGraphId.
+  // Step 1: parentsByGraphId — typed iterator skips the per-edge type
+  // check and the millions of CALLS/ACCESSES/IMPORTS/DEFINES edges
+  // that aren't relevant to MRO.
   const parentsByGraphId = new Map<string, string[]>();
-  for (const rel of graph.iterRelationships()) {
-    if (rel.type !== 'EXTENDS') continue;
+  for (const rel of graph.iterRelationshipsByType('EXTENDS')) {
     let list = parentsByGraphId.get(rel.sourceId);
     if (list === undefined) {
       list = [];
diff --git a/gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts b/gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts
index ee39887a3..ded7c83bd 100644
--- a/gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts
+++ b/gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts
@@ -78,6 +78,14 @@ export const scopeResolutionPhase: PipelinePhase<ScopeResolutionOutput> = {
     deps: ReadonlyMap<string, PhaseResult<unknown>>,
   ): Promise<ScopeResolutionOutput> {
     const { scannedFiles } = getPhaseOutput<StructureOutput>(deps, 'structure');
+    // Reach into the parse phase's AST cache so per-file extract can
+    // skip a second tree-sitter parse. Cache miss is safe (re-parses).
+    // Worker-mode parses leave the cache empty for those files; they
+    // also fall back to a fresh parse — no correctness impact.
+    const { astCache } = getPhaseOutput<{ astCache: { get(path: string): unknown } }>(
+      deps,
+      'parse',
+    );
 
     let totalFiles = 0;
     let totalImports = 0;
@@ -110,6 +118,7 @@ export const scopeResolutionPhase: PipelinePhase<ScopeResolutionOutput> = {
         {
           graph: ctx.graph,
           files,
+          treeCache: astCache,
           onWarn: (msg) => {
             if (isDev) console.warn(`[scope-resolution:${lang}] ${msg}`);
           },
diff --git a/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts b/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
index d294c7144..b8bbf2355 100644
--- a/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
+++ b/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
@@ -42,6 +42,14 @@ export interface RunScopeResolutionInput {
   readonly graph: KnowledgeGraph;
   readonly files: readonly { readonly path: string; readonly content: string }[];
   readonly onWarn?: (message: string) => void;
+  /**
+   * Optional pre-parsed-Tree lookup keyed by file path. When the
+   * pipeline's parse phase ran sequentially, it populated an
+   * `ASTCache`; passing that here lets the per-file extract step
+   * skip a second `tree-sitter parser.parse(...)` call. Cache miss
+   * is safe — falls back to a fresh parse inside the provider.
+   */
+  readonly treeCache?: { get(filePath: string): unknown };
 }
 
 export interface RunScopeResolutionStats {
@@ -65,8 +73,16 @@ export function runScopeResolution(
   // ── Phase 1: extract each file → ParsedFile ────────────────────────────
   const parsedFiles: ParsedFile[] = [];
   let filesSkipped = 0;
+  const treeCache = input.treeCache;
   for (const file of files) {
-    const parsed = extractParsedFile(provider.languageProvider, file.content, file.path, onWarn);
+    const cachedTree = treeCache?.get(file.path);
+    const parsed = extractParsedFile(
+      provider.languageProvider,
+      file.content,
+      file.path,
+      onWarn,
+      cachedTree,
+    );
     if (parsed === undefined) {
       filesSkipped++;
       continue;
diff --git a/gitnexus/test/unit/graph.test.ts b/gitnexus/test/unit/graph.test.ts
index 41bfc8a73..22b06a9be 100644
--- a/gitnexus/test/unit/graph.test.ts
+++ b/gitnexus/test/unit/graph.test.ts
@@ -247,4 +247,63 @@ describe('createKnowledgeGraph', () => {
     expect(remaining[0].sourceId).toBe('fn:b');
     expect(remaining[0].targetId).toBe('fn:c');
   });
+
+  // ─── iterRelationshipsByType ───────────────────────────────────────
+
+  describe('iterRelationshipsByType', () => {
+    it('yields only the requested type', () => {
+      const g = createKnowledgeGraph();
+      g.addRelationship(makeRel('fn:a', 'fn:b', 'CALLS'));
+      g.addRelationship(makeRel('fn:b', 'fn:c', 'CALLS'));
+      g.addRelationship(makeRel('cls:X', 'cls:Y', 'EXTENDS'));
+      g.addRelationship(makeRel('cls:Y', 'cls:Z', 'EXTENDS'));
+
+      expect([...g.iterRelationshipsByType('CALLS')]).toHaveLength(2);
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(2);
+    });
+
+    it('returns a fresh empty iterator when the type has no edges', () => {
+      const g = createKnowledgeGraph();
+      g.addRelationship(makeRel('fn:a', 'fn:b', 'CALLS'));
+      // Two consecutive calls must each be exhaustible — guards against
+      // returning a single shared exhausted iterator.
+      expect([...g.iterRelationshipsByType('IMPLEMENTS')]).toHaveLength(0);
+      expect([...g.iterRelationshipsByType('IMPLEMENTS')]).toHaveLength(0);
+    });
+
+    it('reflects removeRelationship on both indexes', () => {
+      const g = createKnowledgeGraph();
+      g.addRelationship(makeRel('cls:X', 'cls:Y', 'EXTENDS'));
+      g.addRelationship(makeRel('cls:Y', 'cls:Z', 'EXTENDS'));
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(2);
+
+      g.removeRelationship('cls:X-EXTENDS-cls:Y');
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(1);
+      expect(g.relationshipCount).toBe(1);
+    });
+
+    it('reflects removeNode on both indexes', () => {
+      const g = createKnowledgeGraph();
+      g.addNode(makeNode('cls:X', 'X', 'src/x.ts'));
+      g.addNode(makeNode('cls:Y', 'Y', 'src/y.ts'));
+      g.addRelationship(makeRel('cls:X', 'cls:Y', 'EXTENDS'));
+      g.addRelationship(makeRel('cls:X', 'cls:Y', 'IMPLEMENTS'));
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(1);
+      expect([...g.iterRelationshipsByType('IMPLEMENTS')]).toHaveLength(1);
+
+      g.removeNode('cls:Y');
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(0);
+      expect([...g.iterRelationshipsByType('IMPLEMENTS')]).toHaveLength(0);
+      expect([...g.iterRelationships()]).toHaveLength(0);
+    });
+
+    it('dedupes by id across both indexes', () => {
+      const g = createKnowledgeGraph();
+      const rel = makeRel('cls:X', 'cls:Y', 'EXTENDS');
+      g.addRelationship(rel);
+      g.addRelationship(rel); // dedup by id
+      expect([...g.iterRelationshipsByType('EXTENDS')]).toHaveLength(1);
+      expect(g.relationshipCount).toBe(1);
+    });
+  });
 });