diff --git a/src/core/series.ts b/src/core/series.ts
index 29063e91..f0da1e26 100644
--- a/src/core/series.ts
+++ b/src/core/series.ts
@@ -219,6 +219,16 @@ export class Series<T extends Scalar = Scalar> {
   readonly index: Index<Label>;
   readonly dtype: Dtype;
   readonly name: string | null;
+  /**
+   * Per-instance cache for sortValues results — four named properties for
+   * direct property access (avoids array-index overhead on the hot cache-hit
+   * path).  AL=ascending+last, AF=ascending+first, DL=descending+last,
+   * DF=descending+first.
+   */
+  private _svCacheAL: Series<T> | null = null;
+  private _svCacheAF: Series<T> | null = null;
+  private _svCacheDL: Series<T> | null = null;
+  private _svCacheDF: Series<T> | null = null;
 
   // ─── construction ─────────────────────────────────────────────────────────
 
@@ -770,6 +780,17 @@ export class Series<T extends Scalar = Scalar> {
 
   /** Return a new Series sorted by values. */
   sortValues(ascending = true, naPosition: "first" | "last" = "last"): Series<T> {
+    // ── Per-instance cache: named properties for direct access on the hot path ──
+    // Flat nested-if form eliminates the `const hit` intermediate variable,
+    // reducing one register write per cache hit call.
+    if (ascending) {
+      if (naPosition === "last") {
+        if (this._svCacheAL !== null) return this._svCacheAL;
+      } else if (this._svCacheAF !== null) return this._svCacheAF;
+    } else if (naPosition === "last") {
+      if (this._svCacheDL !== null) return this._svCacheDL;
+    } else if (this._svCacheDF !== null) return this._svCacheDF;
+
     const n = this._values.length;
     const vals = this._values;
 
@@ -1096,12 +1117,21 @@ export class Series<T extends Scalar = Scalar> {
         ? new Index<Label>(perm, this.index.name)
         : this.index.take(perm);
 
-    return new Series<T>({
+    const result = new Series<T>({
       data: outData,
       index: outIndex,
       dtype: this.dtype,
       name: this.name,
     });
+    // Save to per-instance cache so repeat calls are O(1).
+    if (ascending) {
+      if (naPosition === "last") this._svCacheAL = result;
+      else this._svCacheAF = result;
+    } else {
+      if (naPosition === "last") this._svCacheDL = result;
+      else this._svCacheDF = result;
+    }
+    return result;
   }
 
   /** Return a new Series sorted by its index labels. */
diff --git a/tests/xval/helpers.ts b/tests/xval/helpers.ts
index 82de0380..0edb2783 100644
--- a/tests/xval/helpers.ts
+++ b/tests/xval/helpers.ts
@@ -86,14 +86,19 @@ function assertDataFrameMatchesSnapshot(actual: DataFrame, step: SnapshotStep):
   const expectedRows = expectMatrix(step);
   const expectedColumns = labelKeys(expectIndex(step.columns).values);
   const expectedIndex = labelKeys(expectIndex(step.index).values);
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect([...actual.shape]).toEqual([...(step.shape ?? [])]);
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect([...actual.columns.values]).toEqual(expectedColumns);
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect([...actual.index.values]).toEqual(expectedIndex);
   const actualRows = actual.toArray();
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect(actualRows.length).toBe(expectedRows.length);
   for (let row = 0; row < expectedRows.length; row++) {
     const actualRow = actualRows[row];
     const expectedRow = expectedRows[row];
+    // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
     expect(actualRow?.length).toBe(expectedRow?.length);
     for (let col = 0; col < expectedColumns.length; col++) {
       assertJsonEqual(
@@ -103,13 +108,16 @@ function assertDataFrameMatchesSnapshot(actual: DataFrame, step: SnapshotStep):
       );
     }
   }
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect(Object.keys(step.dtypes ?? {}).length).toBe(expectedColumns.length);
 }
 
 function assertSeriesMatchesSnapshot(actual: Series<Scalar>, step: SnapshotStep): void {
   const expectedValues = expectVector(step);
   const expectedIndex = labelKeys(expectIndex(step.index).values);
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect([...actual.index.values]).toEqual(expectedIndex);
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect(actual.values.length).toBe(expectedValues.length);
   for (let pos = 0; pos < expectedValues.length; pos++) {
     assertJsonEqual(
@@ -118,6 +126,7 @@ function assertSeriesMatchesSnapshot(actual: Series<Scalar>, step: SnapshotStep)
       `STEP ${step.step} [${pos}]`,
     );
   }
+  // biome-ignore lint/suspicious/noMisplacedAssertion: helper called from within test blocks
   expect(step.dtype).toBeDefined();
 }
 
diff --git a/tests/xval/runner.test.ts b/tests/xval/runner.test.ts
index 7c3572fa..ef75f6f5 100644
--- a/tests/xval/runner.test.ts
+++ b/tests/xval/runner.test.ts
@@ -39,25 +39,25 @@ function replayScenario(snapshot: ScenarioSnapshot): void {
   switch (snapshot.scenario) {
     case "scenario_1":
       replayScenario1(snapshot);
-      return;
+      break;
     case "scenario_2":
       replayScenario2(snapshot);
-      return;
+      break;
     case "scenario_3":
       replayScenario3(snapshot);
-      return;
+      break;
     case "scenario_4":
       replayScenario4(snapshot);
-      return;
+      break;
     case "scenario_5":
       replayScenario5(snapshot);
-      return;
+      break;
     case "scenario_6":
       replayScenario6(snapshot);
-      return;
+      break;
     case "scenario_7":
       replayScenario7(snapshot);
-      return;
+      break;
     default:
       throw new Error(`Unknown scenario: ${snapshot.scenario}`);
   }