test(core): add IPv6 netstat test for findPidByPort + mark _resetShellCache as @internal

- Add test case for IPv6 LISTENING entries ([::]:3000) in Windows netstat output
- Add @internal JSDoc to _resetShellCache to clarify it is test-only

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core/src/__tests__/platform.mock.test.ts

@@ -272,6 +272,21 @@ describe("findPidByPort", () => {
     expect(pid).toBeNull();
   });
 
+  it("finds PID from IPv6 LISTENING line on Windows", async () => {
+    setPlatform("win32");
+    // netstat -ano includes IPv6 entries like [::]:3000 when server binds to all interfaces
+    const netstatOutput = [
+      "  Proto  Local Address          Foreign Address        State           PID",
+      "  TCP    [::]:3000              [::]:0                 LISTENING       55",
+    ].join("\n");
+    resolveExecFile(netstatOutput);
+
+    const mod = await import("../platform.js");
+    const pid = await mod.findPidByPort(3000);
+
+    expect(pid).toBe("55");
+  });
+
   it("returns null when no LISTENING line matches on Windows", async () => {
     setPlatform("win32");
     resolveExecFile("  TCP    0.0.0.0:8080           0.0.0.0:0              LISTENING       99\n");

packages/core/src/platform.ts

@@ -63,7 +63,9 @@ export function getShell(): ShellInfo {
   return cachedShell;
 }
 
-/** Reset cached shell (for testing) */
+/** Reset cached shell (for testing)
+ * @internal
+ */
 export function _resetShellCache(): void {
   cachedShell = null;
 }