fix(process): wait for windows exit code settlement

src/process/exec.ts

@@ -330,7 +330,7 @@ export async function runCommandWithTimeout(
         child.stderr?.destroy();
       }, 250);
     });
-    child.on("close", (code, signal) => {
+    const resolveFromClose = (code: number | null, signal: NodeJS.Signals | null) => {
       if (settled) {
         return;
       }
@@ -363,6 +363,19 @@ export async function runCommandWithTimeout(
         termination,
         noOutputTimedOut,
       });
+    };
+    child.on("close", (code, signal) => {
+      if (
+        childExitState == null &&
+        code == null &&
+        signal == null &&
+        child.exitCode == null &&
+        child.signalCode == null
+      ) {
+        setImmediate(() => resolveFromClose(code, signal));
+        return;
+      }
+      resolveFromClose(code, signal);
     });
   });
 }

src/process/exec.windows.test.ts

@@ -31,6 +31,7 @@ function createMockChild(params?: {
   closeCode?: number | null;
   closeSignal?: NodeJS.Signals | null;
   exitCode?: number | null;
+  exitCodeAfterClose?: number | null;
   signal?: NodeJS.Signals | null;
 }): MockChild {
   const child = new EventEmitter() as MockChild;
@@ -47,6 +48,11 @@ function createMockChild(params?: {
   child.killed = false;
   queueMicrotask(() => {
     child.emit("close", params?.closeCode ?? 0, params?.closeSignal ?? params?.signal ?? null);
+    if (params?.exitCodeAfterClose !== undefined) {
+      setImmediate(() => {
+        child.exitCode = params.exitCodeAfterClose ?? null;
+      });
+    }
   });
   return child;
 }
@@ -117,6 +123,20 @@ describe("windows command wrapper behavior", () => {
     }
   });
 
+  it("waits one tick when Windows close reports null before exitCode settles", async () => {
+    const platformSpy = vi.spyOn(process, "platform", "get").mockReturnValue("win32");
+    const child = createMockChild({ closeCode: null, exitCode: null, exitCodeAfterClose: 0 });
+
+    spawnMock.mockImplementation(() => child);
+
+    try {
+      const result = await runCommandWithTimeout(["npm", "--version"], { timeoutMs: 1000 });
+      expect(result.code).toBe(0);
+    } finally {
+      platformSpy.mockRestore();
+    }
+  });
+
   it("uses cmd.exe wrapper with windowsVerbatimArguments in runExec for .cmd shims", async () => {
     const platformSpy = vi.spyOn(process, "platform", "get").mockReturnValue("win32");
     const expectedComSpec = process.env.ComSpec ?? "cmd.exe";