diff --git a/packages/cli/src/commands/start.ts b/packages/cli/src/commands/start.ts
index 09aada0d5..f9d7f7b29 100644
--- a/packages/cli/src/commands/start.ts
+++ b/packages/cli/src/commands/start.ts
@@ -320,7 +320,7 @@ function ghInstallAttempts(): InstallAttempt[] {
       { cmd: "sudo", args: ["dnf", "install", "-y", "gh"], label: "sudo dnf install -y gh" },
     ];
   }
-  if (process.platform === "win32") {
+  if (isWindows()) {
     return [
       {
         cmd: "winget",
@@ -1625,7 +1625,7 @@ function isLocalPath(arg: string): boolean {
  * the parent process — the user explicitly asked us to stop AO.
  */
 async function sweepWindowsPtyHostsBeforeParentKill(): Promise<void> {
-  if (process.platform !== "win32") return;
+  if (!isWindows()) return;
   try {
     const mod = (await import("@aoagents/ao-plugin-runtime-process")) as {
       sweepWindowsPtyHosts?: () => Promise<{
diff --git a/packages/core/src/atomic-write.ts b/packages/core/src/atomic-write.ts
index deaf076ab..a7f83a582 100644
--- a/packages/core/src/atomic-write.ts
+++ b/packages/core/src/atomic-write.ts
@@ -1,11 +1,11 @@
 import { renameSync, writeFileSync, unlinkSync } from "node:fs";
+import { isWindows } from "./platform.js";
 
 // Windows file-locking workaround. `renameSync` can fail with EPERM/EACCES when
 // antivirus, the Windows indexer, or another process briefly holds a handle on
 // the destination path. The failures are transient — a short retry loop is the
 // standard fix (same pattern Node's own `fs.rm` uses internally).
-const IS_WINDOWS = process.platform === "win32";
-const RENAME_RETRIES = IS_WINDOWS ? 10 : 0;
+const RENAME_RETRIES = isWindows() ? 10 : 0;
 const RENAME_RETRY_DELAY_MS = 50;
 
 function renameWithRetry(src: string, dest: string): void {
diff --git a/packages/web/server/mux-websocket.ts b/packages/web/server/mux-websocket.ts
index 03f4f7117..3a31f3923 100644
--- a/packages/web/server/mux-websocket.ts
+++ b/packages/web/server/mux-websocket.ts
@@ -10,7 +10,7 @@ import { WebSocketServer, WebSocket } from "ws";
 import { spawn } from "node:child_process";
 import { type Socket, connect as netConnect } from "node:net";
 import { findTmux, resolveTmuxSession, resolvePipePath, validateSessionId } from "./tmux-utils.js";
-import { getEnvDefaults } from "@aoagents/ao-core";
+import { getEnvDefaults, isWindows } from "@aoagents/ao-core";
 
 // These types mirror src/lib/mux-protocol.ts exactly.
 // tsconfig.server.json constrains rootDir to "server/", so we cannot import
@@ -503,6 +503,7 @@ export function handleWindowsPipeMessage(
       pipeSocket.on("error", (err) => {
         winPipes.delete(pipeKey);
         winPipeBuffers.delete(pipeKey);
+        pipeSocket.destroy();
         if (ws.readyState === WS_OPEN) {
           ws.send(
             JSON.stringify({
@@ -604,14 +605,14 @@ export function handleWindowsPipeMessage(
 export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer | null {
   // On Windows, we use named pipe relay instead of node-pty/tmux.
   // Allow the server to be created without ptySpawn on Windows.
-  if (!ptySpawn && process.platform !== "win32") {
+  if (!ptySpawn && !isWindows()) {
     console.warn("[MuxServer] node-pty not available — mux WebSocket will be disabled");
     return null;
   }
 
   // On Windows, terminal I/O goes through named pipe relay — no TerminalManager needed.
   const terminalManager =
-    ptySpawn && process.platform !== "win32" ? new TerminalManager(tmuxPath ?? undefined) : null;
+    ptySpawn && !isWindows() ? new TerminalManager(tmuxPath ?? undefined) : null;
 
   const nextPort = process.env.PORT || "3000";
   const broadcaster = new SessionBroadcaster(nextPort);
@@ -669,7 +670,7 @@ export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer |
 
           try {
             if (type === "open") {
-              if (process.platform === "win32") {
+              if (isWindows()) {
                 handleWindowsPipeMessage(
                   msg as { id: string; type: string; projectId?: string; data?: string; cols?: number; rows?: number },
                   ws,
@@ -739,7 +740,7 @@ export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer |
                 }
               }
             } else if (type === "data" && "data" in msg) {
-              if (process.platform === "win32") {
+              if (isWindows()) {
                 handleWindowsPipeMessage(
                   msg as { id: string; type: string; projectId?: string; data: string },
                   ws,
@@ -751,7 +752,7 @@ export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer |
                 terminalManager?.write(id, msg.data, projectId);
               }
             } else if (type === "resize" && "cols" in msg && "rows" in msg) {
-              if (process.platform === "win32") {
+              if (isWindows()) {
                 handleWindowsPipeMessage(
                   msg as { id: string; type: string; projectId?: string; cols: number; rows: number },
                   ws,
@@ -763,7 +764,7 @@ export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer |
                 terminalManager?.resize(id, msg.cols, msg.rows, projectId);
               }
             } else if (type === "close") {
-              if (process.platform === "win32") {
+              if (isWindows()) {
                 handleWindowsPipeMessage(
                   msg as { id: string; type: string; projectId?: string; data?: string; cols?: number; rows?: number },
                   ws,
@@ -840,7 +841,7 @@ export function createMuxWebSocket(tmuxPath?: string | null): WebSocketServer |
       subscriptions.clear();
       // Windows: close all open pipe sockets
       for (const pipeSocket of winPipes.values()) {
-        pipeSocket.end();
+        pipeSocket.destroy();
       }
       winPipes.clear();
       winPipeBuffers.clear();
diff --git a/packages/web/server/tmux-utils.ts b/packages/web/server/tmux-utils.ts
index ba7d82622..7aa5a5a97 100644
--- a/packages/web/server/tmux-utils.ts
+++ b/packages/web/server/tmux-utils.ts
@@ -9,6 +9,7 @@ import { execFileSync } from "node:child_process";
 import { readdirSync, existsSync, readFileSync } from "node:fs";
 import { homedir } from "node:os";
 import { join } from "node:path";
+import { isWindows } from "@aoagents/ao-core";
 
 /** Session ID validation regex — alphanumeric, hyphens, underscores only */
 export const SESSION_ID_PATTERN = /^[a-zA-Z0-9_-]+$/;
@@ -110,7 +111,7 @@ export function validateSessionId(sessionId: string): boolean {
 export function findTmux(
   execFn: typeof execFileSync = execFileSync,
 ): string | null {
-  if (process.platform === "win32") return null;
+  if (isWindows()) return null;
   const candidates = [
     "/opt/homebrew/bin/tmux", // macOS ARM (Homebrew)
     "/usr/local/bin/tmux", // macOS Intel (Homebrew)
@@ -233,7 +234,7 @@ export function resolvePipePath(
     readFile?: (path: string) => string;
   } = defaultFs,
 ): string | null {
-  if (process.platform !== "win32") return null;
+  if (!isWindows()) return null;
 
   const readFile = fs.readFile ?? ((p: string) => readFileSync(p, "utf8"));
   const aoBase = join(fs.homedir(), ".agent-orchestrator");