fix: properly cleanup Windows process tree on Obsidian exit

### Fixed
- Replaced unreliable taskkill /T with PowerShell Get-CimInstance for child process detection in WindowsProcess.ts
- Fixed orphaned node.exe processes when Obsidian closes by killing child processes before parent
- Added proper cleanup when shell: true creates cmd.exe -> node.exe process tree

### Added
- Static currentProcess field to track active process for cleanup during window close
- Static cleanupHandlerRegistered flag to prevent duplicate event handlers
- beforeunload event handler for synchronous cleanup when Obsidian window closes
- killProcessSync method for immediate process termination without async delays
- registerCleanupHandler method to set up window close event listener

### Changed
- Updated start method to store process reference and register cleanup handler
- Modified stop method to use PowerShell child lookup before killing parent process
- Enhanced error handling with try/catch blocks for PowerShell and taskkill operations

src/server/process/WindowsProcess.ts

@@ -2,33 +2,129 @@ import { ChildProcess, spawn, SpawnOptions } from "child_process";
 import { OpenCodeProcess } from "./OpenCodeProcess";
 
 export class WindowsProcess implements OpenCodeProcess {
+  // Static state to track the current process for cleanup
+  private static currentProcess: ChildProcess | null = null;
+  private static cleanupHandlerRegistered = false;
+
   start(
     command: string,
     args: string[],
     options: SpawnOptions
   ): ChildProcess {
-    return spawn(command, args, {
+    const process = spawn(command, args, {
       ...options,
       shell: true,
       windowsHide: true,
     });
+
+    // Store process for cleanup
+    WindowsProcess.currentProcess = process;
+    WindowsProcess.registerCleanupHandler();
+
+    return process;
   }
 
   async stop(process: ChildProcess): Promise<void> {
     const pid = process.pid;
     if (!pid) {
+      WindowsProcess.currentProcess = null;
       return;
     }
 
     console.log("[OpenCode] Stopping server process tree, PID:", pid);
 
-    // Use taskkill with /T flag to kill process tree
-    await this.execAsync(`taskkill /T /F /PID ${pid}`);
+    // Method 1: Find and kill child processes (actual node.exe) using PowerShell
+    // This is necessary because shell: true spawns cmd.exe -> node.exe, and
+    // killing cmd.exe leaves node.exe orphaned
+    try {
+      const { execSync } = require("child_process");
+      const output = execSync(
+        `powershell -Command "Get-CimInstance Win32_Process -Filter \\"ParentProcessId=${pid}\\" | Select-Object ProcessId"`,
+        { encoding: "utf8", stdio: ["pipe", "pipe", "ignore"] }
+      );
+
+      const lines = output.split("\n").slice(3); // Skip headers
+      for (const line of lines) {
+        const childPid = line.trim();
+        if (childPid && !isNaN(parseInt(childPid))) {
+          try {
+            execSync(`taskkill /F /PID ${childPid}`, { stdio: "ignore" });
+          } catch {
+            // Child may already be gone
+          }
+        }
+      }
+    } catch {
+      // PowerShell lookup failed, continue to other methods
+    }
+
+    // Method 2: Kill the parent process (cmd.exe)
+    try {
+      await this.execAsync(`taskkill /F /PID ${pid}`);
+    } catch {
+      // Parent may already be gone
+    }
+
+    // Clear stored process
+    WindowsProcess.currentProcess = null;
 
     // Wait for process to exit
     await this.waitForExit(process, 5000);
   }
 
+  private static registerCleanupHandler(): void {
+    if (WindowsProcess.cleanupHandlerRegistered) {
+      return;
+    }
+
+    // Register beforeunload handler for window close cleanup
+    if (typeof window !== "undefined") {
+      window.addEventListener("beforeunload", () => {
+        if (WindowsProcess.currentProcess?.pid) {
+          WindowsProcess.killProcessSync(WindowsProcess.currentProcess.pid);
+        }
+      });
+      WindowsProcess.cleanupHandlerRegistered = true;
+    }
+  }
+
+  private static killProcessSync(pid: number): void {
+    try {
+      const { execSync } = require("child_process");
+
+      // Method 1: Kill child processes using PowerShell
+      try {
+        const output = execSync(
+          `powershell -Command "Get-CimInstance Win32_Process -Filter \\"ParentProcessId=${pid}\\" | Select-Object ProcessId"`,
+          { encoding: "utf8", stdio: ["pipe", "pipe", "ignore"] }
+        );
+
+        const lines = output.split("\n").slice(3);
+        for (const line of lines) {
+          const childPid = line.trim();
+          if (childPid && !isNaN(parseInt(childPid))) {
+            try {
+              execSync(`taskkill /F /PID ${childPid}`, { stdio: "ignore" });
+            } catch {
+              // Child may already be gone
+            }
+          }
+        }
+      } catch {
+        // PowerShell lookup failed
+      }
+
+      // Method 2: Kill parent process
+      try {
+        execSync(`taskkill /F /PID ${pid}`, { stdio: "ignore" });
+      } catch {
+        // Parent may already be gone
+      }
+    } catch {
+      // Process may already be gone
+    }
+  }
+
   async verifyCommand(command: string): Promise<string | null> {
     // Use 'where' command to check if executable exists in PATH
     try {