diff --git a/gitnexus/src/core/ingestion/parsing-processor.ts b/gitnexus/src/core/ingestion/parsing-processor.ts
index 88d8cd1210..c91df29536 100644
--- a/gitnexus/src/core/ingestion/parsing-processor.ts
+++ b/gitnexus/src/core/ingestion/parsing-processor.ts
@@ -58,6 +58,39 @@ export interface WorkerExtractedData {
   parsedFiles: ParsedFile[];
 }
 
+type ParsedGraphNode = ParseWorkerResult['nodes'][number];
+
+function compareText(left: string, right: string): number {
+  return left < right ? -1 : left > right ? 1 : 0;
+}
+
+function sourceLine(node: ParsedGraphNode): number {
+  const value = node.properties.startLine;
+  return typeof value === 'number' && Number.isFinite(value) ? value : Number.MAX_SAFE_INTEGER;
+}
+
+function compareParsedNodeSourceOrder(left: ParsedGraphNode, right: ParsedGraphNode): number {
+  const leftPath = typeof left.properties.filePath === 'string' ? left.properties.filePath : '';
+  const rightPath = typeof right.properties.filePath === 'string' ? right.properties.filePath : '';
+  const fileOrder = compareText(leftPath, rightPath);
+  if (fileOrder !== 0) return fileOrder;
+
+  const leftLine = sourceLine(left);
+  const rightLine = sourceLine(right);
+  if (leftLine !== rightLine) return leftLine < rightLine ? -1 : 1;
+
+  return compareText(left.id, right.id);
+}
+
+function nodesInSourceOrder(nodes: readonly ParsedGraphNode[]): readonly ParsedGraphNode[] {
+  for (let index = 1; index < nodes.length; index++) {
+    if (compareParsedNodeSourceOrder(nodes[index - 1], nodes[index]) > 0) {
+      return [...nodes].sort(compareParsedNodeSourceOrder);
+    }
+  }
+  return nodes;
+}
+
 // ============================================================================
 // Worker-based parallel parsing
 // ============================================================================
@@ -95,7 +128,11 @@ export const mergeChunkResults = (
   const allParsedFiles: ParsedFile[] = [];
 
   for (const result of chunkResults) {
-    for (const node of result.nodes) {
+    // Worker jobs and input files are already merged in stable start-index/path
+    // order. Canonicalize the final per-result node boundary once so graph
+    // insertion, cache replay, and first-wins graph indexes share source order.
+    // The common already-ordered path stays allocation-free and linear.
+    for (const node of nodesInSourceOrder(result.nodes)) {
       graph.addNode({
         id: node.id,
         label: node.label as NodeLabel,
diff --git a/gitnexus/src/core/ingestion/scope-resolution/graph-bridge/node-lookup.ts b/gitnexus/src/core/ingestion/scope-resolution/graph-bridge/node-lookup.ts
index 9ab1649a18..0d5abe5103 100644
--- a/gitnexus/src/core/ingestion/scope-resolution/graph-bridge/node-lookup.ts
+++ b/gitnexus/src/core/ingestion/scope-resolution/graph-bridge/node-lookup.ts
@@ -163,7 +163,7 @@ export function buildGraphNodeLookup(graph: KnowledgeGraph): GraphNodeLookup {
       }
     }
 
-    // Fallback key: simple name. First-wins within a file — used when
+    // Fallback key: simple name. Source-order first-wins within a file — used when
     // the caller doesn't know the qualifier (unqualified free-call
     // fallback, cross-file resolution where MethodRegistry already
     // disambiguated the owner).
diff --git a/gitnexus/test/unit/scope-resolution/node-lookup-determinism.test.ts b/gitnexus/test/unit/scope-resolution/node-lookup-determinism.test.ts
new file mode 100644
index 0000000000..852ab09f75
--- /dev/null
+++ b/gitnexus/test/unit/scope-resolution/node-lookup-determinism.test.ts
@@ -0,0 +1,94 @@
+import type { NodeLabel } from 'gitnexus-shared';
+import { describe, expect, it } from 'vitest';
+
+import { createKnowledgeGraph } from '../../../src/core/graph/graph.js';
+import { createSemanticModel } from '../../../src/core/ingestion/model/semantic-model.js';
+import { mergeChunkResults } from '../../../src/core/ingestion/parsing-processor.js';
+import {
+  buildGraphNodeLookup,
+  qualifiedKey,
+  simpleKey,
+} from '../../../src/core/ingestion/scope-resolution/graph-bridge/node-lookup.js';
+import type { ParseWorkerResult } from '../../../src/core/ingestion/workers/parse-worker.js';
+
+const FILE = 'src/service.ts';
+
+interface Candidate {
+  id: string;
+  startLine?: number;
+}
+
+function buildLookup(candidates: readonly Candidate[]) {
+  const graph = createKnowledgeGraph();
+  const nodes = candidates.map(
+    (candidate) =>
+      ({
+        id: candidate.id,
+        label: 'Method' as NodeLabel,
+        properties: {
+          name: 'save',
+          qualifiedName: 'Service.save',
+          filePath: FILE,
+          ...(candidate.startLine !== undefined ? { startLine: candidate.startLine } : {}),
+        },
+      }) satisfies ParseWorkerResult['nodes'][number],
+  );
+  const result: ParseWorkerResult = {
+    nodes,
+    relationships: [],
+    symbols: [],
+    calls: [],
+    assignments: [],
+    routes: [],
+    fetchCalls: [],
+    fetchWrapperDefs: [],
+    decoratorRoutes: [],
+    routerIncludes: [],
+    routerImports: [],
+    toolDefs: [],
+    ormQueries: [],
+    constructorBindings: [],
+    fileScopeBindings: [],
+    parsedFiles: [],
+    skippedLanguages: {},
+    fileCount: 1,
+  };
+
+  mergeChunkResults(graph, createSemanticModel().symbols, [result]);
+  return buildGraphNodeLookup(graph);
+}
+
+describe('parse-result graph insertion determinism', () => {
+  it('selects the earliest source definition regardless of worker result order', () => {
+    const early = { id: `Method:${FILE}:Service.save#1`, startLine: 10 };
+    const late = { id: `Method:${FILE}:Service.save#2`, startLine: 20 };
+
+    const lateFirst = buildLookup([late, early]);
+    const earlyFirst = buildLookup([early, late]);
+
+    for (const key of [simpleKey(FILE, 'save'), qualifiedKey(FILE, 'Method', 'Service.save')]) {
+      expect(lateFirst.get(key)).toBe(early.id);
+      expect(earlyFirst.get(key)).toBe(early.id);
+    }
+  });
+
+  it('uses the stable node id when source positions are identical', () => {
+    const first = { id: `Method:${FILE}:Service.save#1`, startLine: 10 };
+    const second = { id: `Method:${FILE}:Service.save#2`, startLine: 10 };
+
+    const firstLookup = buildLookup([second, first]);
+    const secondLookup = buildLookup([first, second]);
+
+    expect(firstLookup.get(simpleKey(FILE, 'save'))).toBe(first.id);
+    expect(secondLookup.get(simpleKey(FILE, 'save'))).toBe(first.id);
+  });
+
+  it('uses the stable node id when source positions are unavailable', () => {
+    const first = { id: `Method:${FILE}:Service.save#1` };
+    const second = { id: `Method:${FILE}:Service.save#2` };
+
+    const lookup = buildLookup([second, first]);
+
+    expect(lookup.get(simpleKey(FILE, 'save'))).toBe(first.id);
+  });
+});