diff --git a/src/shared/config-eval.test.ts b/src/shared/config-eval.test.ts
index 48ddb9e3298..7891c17142c 100644
--- a/src/shared/config-eval.test.ts
+++ b/src/shared/config-eval.test.ts
@@ -1,12 +1,40 @@
-import { describe, expect, it } from "vitest";
+import fs from "node:fs";
+import path from "node:path";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   evaluateRuntimeEligibility,
   evaluateRuntimeRequires,
+  hasBinary,
   isConfigPathTruthyWithDefaults,
   isTruthy,
   resolveConfigPath,
+  resolveRuntimePlatform,
 } from "./config-eval.js";
 
+const originalPlatformDescriptor = Object.getOwnPropertyDescriptor(process, "platform");
+const originalPath = process.env.PATH;
+const originalPathExt = process.env.PATHEXT;
+
+function setPlatform(platform: NodeJS.Platform): void {
+  Object.defineProperty(process, "platform", {
+    value: platform,
+    configurable: true,
+  });
+}
+
+afterEach(() => {
+  vi.restoreAllMocks();
+  process.env.PATH = originalPath;
+  if (originalPathExt === undefined) {
+    delete process.env.PATHEXT;
+  } else {
+    process.env.PATHEXT = originalPathExt;
+  }
+  if (originalPlatformDescriptor) {
+    Object.defineProperty(process, "platform", originalPlatformDescriptor);
+  }
+});
+
 describe("config-eval helpers", () => {
   it("normalizes truthy values across primitive types", () => {
     expect(isTruthy(undefined)).toBe(false);
@@ -51,6 +79,53 @@ describe("config-eval helpers", () => {
     ).toBe(true);
     expect(isConfigPathTruthyWithDefaults(config, "browser.other", {})).toBe(false);
   });
+
+  it("returns the active runtime platform", () => {
+    setPlatform("darwin");
+    expect(resolveRuntimePlatform()).toBe("darwin");
+  });
+
+  it("caches binary lookups until PATH changes", () => {
+    process.env.PATH = ["/missing/bin", "/found/bin"].join(path.delimiter);
+    const accessSpy = vi.spyOn(fs, "accessSync").mockImplementation((candidate) => {
+      if (String(candidate) === path.join("/found/bin", "tool")) {
+        return undefined;
+      }
+      throw new Error("missing");
+    });
+
+    expect(hasBinary("tool")).toBe(true);
+    expect(hasBinary("tool")).toBe(true);
+    expect(accessSpy).toHaveBeenCalledTimes(2);
+
+    process.env.PATH = "/other/bin";
+    accessSpy.mockClear();
+    accessSpy.mockImplementation(() => {
+      throw new Error("missing");
+    });
+
+    expect(hasBinary("tool")).toBe(false);
+    expect(accessSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it("checks PATHEXT candidates on Windows", () => {
+    setPlatform("win32");
+    process.env.PATH = "/tools";
+    process.env.PATHEXT = ".EXE;.CMD";
+    const accessSpy = vi.spyOn(fs, "accessSync").mockImplementation((candidate) => {
+      if (String(candidate) === "/tools/tool.CMD") {
+        return undefined;
+      }
+      throw new Error("missing");
+    });
+
+    expect(hasBinary("tool")).toBe(true);
+    expect(accessSpy.mock.calls.map(([candidate]) => String(candidate))).toEqual([
+      "/tools/tool",
+      "/tools/tool.EXE",
+      "/tools/tool.CMD",
+    ]);
+  });
 });
 
 describe("evaluateRuntimeRequires", () => {