perf(javascript): cache canonical export comparison sort keys (#1028)

src/domain/javascript/javascriptExportShapeComparison.ts

@@ -1,5 +1,8 @@
-import { uniqueSorted } from "../canonicalOrdering.js";
-import { digestExportShapeValue } from "./javascriptExportShapeComparisonIdentity.js";
+import { compareCodePoints, uniqueSorted } from "../canonicalOrdering.js";
+import {
+  canonicalExportShapeValue,
+  digestExportShapeValue,
+} from "./javascriptExportShapeComparisonIdentity.js";
 import {
   javaScriptExportShapeComparisonResultSchema,
   type JavaScriptExportShapeComparisonChange,
@@ -14,7 +17,6 @@ import {
 } from "./javascriptExportShapeSelection.js";
 import {
   buildJavaScriptExportShapeChanges,
-  compareJavaScriptExportShapeChanges,
   hasPartialJavaScriptExportPropertyCoverage,
   pairJavaScriptExportShapeVariants,
   type JavaScriptExportShapePairing,
@@ -42,14 +44,16 @@ export const compareJavaScriptExportShapes = (
     input.left.evidenceId,
     input.right.evidenceId,
   );
-  const allChanges = buildJavaScriptExportShapeChanges({
-    leftSelection: left,
-    rightSelection: right,
-    pairing,
-    leftShapes: leftRetained.shapes,
-    rightShapes: rightRetained.shapes,
-    evidenceLinks,
-  }).sort(compareJavaScriptExportShapeChanges);
+  const allChanges = sortChanges(
+    buildJavaScriptExportShapeChanges({
+      leftSelection: left,
+      rightSelection: right,
+      pairing,
+      leftShapes: leftRetained.shapes,
+      rightShapes: rightRetained.shapes,
+      evidenceLinks,
+    }),
+  );
   const changes = allChanges;
   const omittedChanges = 0;
   const coverage = comparisonCoverage({
@@ -78,6 +82,29 @@ export const compareJavaScriptExportShapes = (
   });
 };
 
+const sortChanges = (
+  changes: readonly JavaScriptExportShapeComparisonChange[],
+): JavaScriptExportShapeComparisonChange[] =>
+  changes
+    .map((change, index) => ({
+      change,
+      index,
+      sortKey: canonicalExportShapeValue({
+        discriminant: change.discriminant,
+        path: change.path,
+        status: change.status,
+        left_source_range: change.left_source_range,
+        right_source_range: change.right_source_range,
+        change_id: change.change_id,
+      }),
+    }))
+    .sort(
+      (left, right) =>
+        compareCodePoints(left.sortKey, right.sortKey) ||
+        left.index - right.index,
+    )
+    .map(({ change }) => change);
+
 interface CoverageInput {
   readonly input: JavaScriptExportShapeComparisonProjectionInput;
   readonly left: SelectedJavaScriptExport;

src/domain/javascript/javascriptExportShapeVariants.ts

@@ -112,16 +112,6 @@ export const buildJavaScriptExportShapeChanges = (
   return [...paired, ...unpairedLeft, ...unpairedRight];
 };
 
-/** Sort changes by semantic content rather than traversal order. */
-export const compareJavaScriptExportShapeChanges = (
-  left: JavaScriptExportShapeComparisonChange,
-  right: JavaScriptExportShapeComparisonChange,
-): number =>
-  compareCodePoints(
-    canonicalExportShapeValue(changeSortKey(left)),
-    canonicalExportShapeValue(changeSortKey(right)),
-  );
-
 /** Report whether any retained shape lacks complete property coverage. */
 export const hasPartialJavaScriptExportPropertyCoverage = (
   shapes: readonly Shape[],
@@ -429,15 +419,6 @@ const changeWithId = (
   change_id: `jesc_change_${digestExportShapeValue(semantic)}`,
 });
 
-const changeSortKey = (change: JavaScriptExportShapeComparisonChange) => ({
-  discriminant: change.discriminant,
-  path: change.path,
-  status: change.status,
-  left_source_range: change.left_source_range,
-  right_source_range: change.right_source_range,
-  change_id: change.change_id,
-});
-
 const literalValue = (
   field: Field,
 ):

tests/acceptance/applications/applicationExportShapeMcp.test.ts

@@ -135,9 +135,13 @@ describe("source-produced export comparison inventories", () => {
         `export const candidate${String(index)} = ${String(index)};`,
     ).join("\n");
     const inventorySource = `export default function parse(value) {\n${returnSites}\n  throw new Error("no match");\n}\n${extraExports}`;
+    const pairedVariantsSource = `export default function parse(value) {
+${returnSites}
+  throw new Error("no match");
+}`;
     const [inventoryLeft, inventoryRight] = await Promise.all([
       analyzeSourceEvidence(inventorySource),
-      analyzeSourceEvidence(inventorySource),
+      analyzeSourceEvidence(pairedVariantsSource),
     ]);
     const variants = compareEvidence(inventoryLeft, inventoryRight);
     expect(variants.left).toMatchObject({ status: "selected" });

tests/boundary/filesystem/javascriptExportShapeComparison.test.ts

@@ -88,6 +88,21 @@ describe("JavaScript export return-shape comparison", () => {
     expect(result.coverage.status).toBe("partial");
   });
 
+  it("orders multiple changed paths deterministically across Unicode names", async () => {
+    const graphs = await analyzeSources({
+      left: `export default () => ({ type: "item", zeta: 1, alpha: 1, "éclair": 1 });`,
+      right: `export default () => ({ type: "item", zeta: 2, alpha: 2, "éclair": 2 });`,
+    });
+    const first = compare(...graphs);
+    const second = compare(...graphs);
+
+    expect(new Set(first.changes.map(({ path }) => path))).toEqual(
+      new Set(["/alpha", "/zeta", "/éclair"]),
+    );
+    expect(first.changes).toEqual(second.changes);
+    expect(first.comparison_id).toBe(second.comparison_id);
+  });
+
   it("does not pair discriminants that an unknown trailing spread can overwrite", async () => {
     const [left, right] = await analyzeSources({
       left: `