test(reference): cover failure normalization

src/application/ReferenceSourceImport.ts

@@ -67,6 +67,27 @@ const deduplicateRelationships = (
   return result;
 };
 
+/** Sort parse failures deterministically while retaining distinct reasons. */
+export const normalizeHistoricalSourceParseFailures = (
+  failures: HistoricalSourceGraphInput["parse_failures"],
+): HistoricalSourceGraphInput["parse_failures"] =>
+  [...failures]
+    .sort((left, right) =>
+      byCodePoint(
+        historicalSourceParseFailureKey(left),
+        historicalSourceParseFailureKey(right),
+      ),
+    )
+    .filter((value, index, array) => {
+      if (index === 0) return true;
+      const previous = array[index - 1];
+      return (
+        previous === undefined ||
+        historicalSourceParseFailureKey(value) !==
+          historicalSourceParseFailureKey(previous)
+      );
+    });
+
 const buildProvenance = (
   options: ReferenceSourceImportOptions,
 ): HistoricalSourceGraphInput["provenance"] => ({
@@ -205,22 +226,7 @@ export const importReferenceSource = async (
   if (isAborted(options.signal)) return err(cancelled());
 
   const uniqueRelationships = deduplicateRelationships(relationships);
-  const uniqueFailures = [...parseFailures]
-    .sort((left, right) =>
-      byCodePoint(
-        historicalSourceParseFailureKey(left),
-        historicalSourceParseFailureKey(right),
-      ),
-    )
-    .filter((value, index, array) => {
-      if (index === 0) return true;
-      const previous = array[index - 1];
-      if (previous === undefined) return true;
-      return (
-        historicalSourceParseFailureKey(value) !==
-        historicalSourceParseFailureKey(previous)
-      );
-    });
+  const uniqueFailures = normalizeHistoricalSourceParseFailures(parseFailures);
 
   const sortedEntries = [...entries].sort((left, right) =>
     byCodePoint(left.path, right.path),

tests/referenceSourceImport.test.ts

@@ -6,7 +6,10 @@ import { join } from "node:path";
 import { add, commit, init } from "isomorphic-git";
 import { describe, expect, it } from "vitest";
 
-import { importReferenceSource } from "../src/application/ReferenceSourceImport.js";
+import {
+  importReferenceSource,
+  normalizeHistoricalSourceParseFailures,
+} from "../src/application/ReferenceSourceImport.js";
 import { projectReferenceSourceEntryFailure } from "../src/application/ReferenceSourceImportEntries.js";
 import {
   projectReferenceSourceImportError,
@@ -52,6 +55,27 @@ const importTree = (
   });
 
 describe("reference source import", () => {
+  it("deduplicates exact parse failures without collapsing distinct reasons", () => {
+    const malformed = {
+      path: "src/main.ts",
+      parser: "babel",
+      reason: "Malformed input",
+    };
+    const unexpected = {
+      path: "src/main.ts",
+      parser: "babel",
+      reason: "Unexpected token",
+    };
+
+    expect(
+      normalizeHistoricalSourceParseFailures([
+        unexpected,
+        malformed,
+        unexpected,
+      ]),
+    ).toEqual([malformed, unexpected]);
+  });
+
   it("projects entry failures without low-level reader diagnostics", () => {
     for (const [kind, code] of [
       ["directory", "io"],