refactor(infra): share shell env timeout normalization

src/infra/shell-env.test.ts

@@ -1,6 +1,8 @@
 import { describe, expect, it, vi } from "vitest";
 import {
+  getShellPathFromLoginShell,
   loadShellEnvFallback,
+  resetShellPathCacheForTests,
   resolveShellEnvFallbackTimeoutMs,
   shouldEnableShellEnvFallback,
 } from "./shell-env.js";
@@ -71,4 +73,42 @@ describe("shell env fallback", () => {
     expect(env.DISCORD_BOT_TOKEN).toBe("discord");
     expect(exec2).not.toHaveBeenCalled();
   });
+
+  it("resolves PATH via login shell and caches it", () => {
+    resetShellPathCacheForTests();
+    const exec = vi.fn(() => Buffer.from("PATH=/usr/local/bin:/usr/bin\0HOME=/tmp\0"));
+
+    const first = getShellPathFromLoginShell({
+      env: {} as NodeJS.ProcessEnv,
+      exec: exec as unknown as Parameters<typeof getShellPathFromLoginShell>[0]["exec"],
+    });
+    const second = getShellPathFromLoginShell({
+      env: {} as NodeJS.ProcessEnv,
+      exec: exec as unknown as Parameters<typeof getShellPathFromLoginShell>[0]["exec"],
+    });
+
+    expect(first).toBe("/usr/local/bin:/usr/bin");
+    expect(second).toBe("/usr/local/bin:/usr/bin");
+    expect(exec).toHaveBeenCalledOnce();
+  });
+
+  it("returns null on shell env read failure and caches null", () => {
+    resetShellPathCacheForTests();
+    const exec = vi.fn(() => {
+      throw new Error("exec failed");
+    });
+
+    const first = getShellPathFromLoginShell({
+      env: {} as NodeJS.ProcessEnv,
+      exec: exec as unknown as Parameters<typeof getShellPathFromLoginShell>[0]["exec"],
+    });
+    const second = getShellPathFromLoginShell({
+      env: {} as NodeJS.ProcessEnv,
+      exec: exec as unknown as Parameters<typeof getShellPathFromLoginShell>[0]["exec"],
+    });
+
+    expect(first).toBeNull();
+    expect(second).toBeNull();
+    expect(exec).toHaveBeenCalledOnce();
+  });
 });