diff --git a/scripts/gen-doc-graphs.spec.ts b/scripts/gen-doc-graphs.spec.ts
index b529fc4c50..057054734e 100644
--- a/scripts/gen-doc-graphs.spec.ts
+++ b/scripts/gen-doc-graphs.spec.ts
@@ -9,7 +9,7 @@ import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { dirname, join } from 'node:path'
 import { afterAll, describe, expect, it } from 'vitest'
-import { EventRelationCollector, type PackageSource } from './gen-doc-graphs.ts'
+import { collectPackageSources, EventRelationCollector } from './gen-doc-graphs.ts'
 import { TypeScriptProject } from './ts-project.ts'
 
 const FIXTURE: Record<string, string> = {
@@ -69,11 +69,7 @@ for (const [rel, content] of Object.entries(FIXTURE)) {
   writeFileSync(join(root, rel), content)
 }
 const project = new TypeScriptProject(root)
-const sources = project.sourceFiles().flatMap((sourceFile): PackageSource[] => {
-  const rel = project.relativePath(sourceFile)
-  const match = /^packages\/[^/]+\/([^/]+)\/src\/.+\.ts$/.exec(rel)
-  return match?.[1] ? [{ rel, pkg: match[1], sourceFile }] : []
-}).sort((left, right) => left.rel.localeCompare(right.rel))
+const sources = collectPackageSources(project)
 
 afterAll(() => {
   rmSync(root, { recursive: true, force: true })
diff --git a/scripts/gen-doc-graphs.ts b/scripts/gen-doc-graphs.ts
index b80885726f..23250e19e8 100644
--- a/scripts/gen-doc-graphs.ts
+++ b/scripts/gen-doc-graphs.ts
@@ -1050,14 +1050,22 @@ function unionSets<T>(left: ReadonlySet<T>, right: ReadonlySet<T>): Set<T> {
   return out
 }
 
-function collectEventRelations(): Map<string, EventRelation> {
-  const project = new TypeScriptProject(root)
-  const sources = project.sourceFiles().flatMap((sourceFile): PackageSource[] => {
+/**
+ * Select the package source files of one project in deterministic order.
+ * @param project - the loaded repository TypeScript project.
+ * @returns `packages/<group>/<pkg>/src` files tagged with their package name.
+ */
+export function collectPackageSources(project: TypeScriptProject): PackageSource[] {
+  return project.sourceFiles().flatMap((sourceFile): PackageSource[] => {
     const rel = project.relativePath(sourceFile)
     const match = /^packages\/[^/]+\/([^/]+)\/src\/.+\.ts$/.exec(rel)
     return match?.[1] ? [{ rel, pkg: match[1], sourceFile }] : []
   }).sort((left, right) => left.rel.localeCompare(right.rel))
-  return new EventRelationCollector(project, sources).collect()
+}
+
+function collectEventRelations(): Map<string, EventRelation> {
+  const project = new TypeScriptProject(root)
+  return new EventRelationCollector(project, collectPackageSources(project)).collect()
 }
 
 function relationPackages(map: Map<string, Set<string>>, pkgsByShort: Map<string, Pkg>): string {