diff --git a/scripts/lib/extension-test-plan.mjs b/scripts/lib/extension-test-plan.mjs
index 9b658706931..5a6d687f3e7 100644
--- a/scripts/lib/extension-test-plan.mjs
+++ b/scripts/lib/extension-test-plan.mjs
@@ -1,3 +1,4 @@
+import { spawnSync } from "node:child_process";
 import fs from "node:fs";
 import path from "node:path";
 import { channelTestRoots } from "../../test/vitest/vitest.channel-paths.mjs";
@@ -64,7 +65,46 @@ function normalizeRelative(inputPath) {
   return inputPath.split(path.sep).join("/");
 }
 
+function isPathInsideRepo(relativePath) {
+  return relativePath !== ".." && !relativePath.startsWith("../") && !path.isAbsolute(relativePath);
+}
+
+function isSkippedTrackedTestFile(relativePath) {
+  return relativePath.split("/").some((segment) => segment === "dist" || segment === "node_modules");
+}
+
+function listTrackedTestFiles(rootPath) {
+  const relativeRoot = normalizeRelative(path.relative(repoRoot, rootPath));
+  if (!isPathInsideRepo(relativeRoot)) {
+    return null;
+  }
+
+  const result = spawnSync("git", ["ls-files", "--", relativeRoot], {
+    cwd: repoRoot,
+    encoding: "utf8",
+    stdio: ["ignore", "pipe", "ignore"],
+  });
+  if (result.status !== 0) {
+    return null;
+  }
+
+  return result.stdout
+    .split("\n")
+    .map((line) => line.trim().replaceAll("\\", "/"))
+    .filter(
+      (line) =>
+        line.length > 0 &&
+        !isSkippedTrackedTestFile(line) &&
+        (line.endsWith(".test.ts") || line.endsWith(".test.tsx")),
+    );
+}
+
 function countTestFiles(rootPath) {
+  const trackedFiles = listTrackedTestFiles(rootPath);
+  if (trackedFiles) {
+    return trackedFiles.length;
+  }
+
   let total = 0;
   const stack = [rootPath];
 
diff --git a/test/scripts/test-extension.test.ts b/test/scripts/test-extension.test.ts
index 8329c89b813..3926012b549 100644
--- a/test/scripts/test-extension.test.ts
+++ b/test/scripts/test-extension.test.ts
@@ -424,6 +424,52 @@ describe("scripts/test-extension.mjs", () => {
     ]);
   });
 
+  it("counts tracked extension tests without walking extension directories", () => {
+    const output = execFileSync(
+      process.execPath,
+      [
+        "--input-type=module",
+        "--eval",
+        `
+          import fs from "node:fs";
+          import { syncBuiltinESMExports } from "node:module";
+          const counts = { readdirSync: 0 };
+          const originalReaddirSync = fs.readdirSync;
+          fs.readdirSync = (...args) => {
+            counts.readdirSync += 1;
+            return originalReaddirSync(...args);
+          };
+          syncBuiltinESMExports();
+          const { createExtensionTestShards, resolveExtensionBatchPlan } = await import("./scripts/lib/extension-test-plan.mjs");
+          const extensionIds = ["matrix", "openai", "slack", "telegram"];
+          const batch = resolveExtensionBatchPlan({ cwd: process.cwd(), extensionIds });
+          const shards = createExtensionTestShards({ cwd: process.cwd(), extensionIds, shardCount: 2 });
+          console.log(JSON.stringify({
+            batchTests: batch.testFileCount,
+            counts,
+            shards: shards.length,
+            shardTests: shards.reduce((total, shard) => total + shard.testFileCount, 0),
+          }));
+        `,
+      ],
+      {
+        cwd: process.cwd(),
+        encoding: "utf8",
+      },
+    );
+
+    const payload = JSON.parse(output) as {
+      batchTests: number;
+      counts: { readdirSync: number };
+      shards: number;
+      shardTests: number;
+    };
+    expect(payload.batchTests).toBeGreaterThan(0);
+    expect(payload.shards).toBe(2);
+    expect(payload.shardTests).toBe(payload.batchTests);
+    expect(payload.counts.readdirSync).toBe(0);
+  });
+
   it("balances extension test shards by estimated CI cost", () => {
     const shards = createExtensionTestShards({
       cwd: process.cwd(),