fix(coding-agent): fix Windows self-update

Fixes #3857

packages/coding-agent/src/config.ts

@@ -1,5 +1,5 @@
 import { spawnSync } from "child_process";
-import { existsSync, readFileSync } from "fs";
+import { existsSync, readFileSync, realpathSync } from "fs";
 import { homedir } from "os";
 import { dirname, join, resolve, sep } from "path";
 import { fileURLToPath } from "url";
@@ -94,6 +94,9 @@ function readCommandOutput(command: string, args: string[]): string | undefined
 		encoding: "utf-8",
 		stdio: ["ignore", "pipe", "ignore"],
 		timeout: 2000,
+		// Windows package managers are commonly .cmd shims. Use the shell so Node can execute them;
+		// command and args are fixed literals from getGlobalPackageRoots(), not user input.
+		shell: process.platform === "win32",
 	});
 	if (result.status !== 0) return undefined;
 	const stdout = result.stdout.trim();
@@ -128,18 +131,32 @@ function getGlobalPackageRoots(method: InstallMethod): string[] {
 	}
 }
 
-function isManagedByGlobalPackageManager(method: InstallMethod): boolean {
-	let packageDir = resolve(getPackageDir());
+function normalizeExistingPathForComparison(path: string): string | undefined {
+	const resolvedPath = resolve(path);
+	if (!existsSync(resolvedPath)) {
+		return undefined;
+	}
+	let normalizedPath: string;
+	try {
+		normalizedPath = realpathSync(resolvedPath);
+	} catch {
+		return undefined;
+	}
 	if (process.platform === "win32") {
-		packageDir = packageDir.toLowerCase();
+		normalizedPath = normalizedPath.toLowerCase();
+	}
+	return normalizedPath;
+}
+
+function isManagedByGlobalPackageManager(method: InstallMethod): boolean {
+	const packageDir = normalizeExistingPathForComparison(getPackageDir());
+	if (!packageDir) {
+		return false;
 	}
 	return getGlobalPackageRoots(method).some((root) => {
-		let normalizedRoot = resolve(root);
-		if (process.platform === "win32") {
-			normalizedRoot = normalizedRoot.toLowerCase();
-		}
+		const normalizedRoot = normalizeExistingPathForComparison(root);
 		return (
-			existsSync(normalizedRoot) &&
+			normalizedRoot !== undefined &&
 			(packageDir === normalizedRoot ||
 				packageDir.startsWith(normalizedRoot.endsWith(sep) ? normalizedRoot : `${normalizedRoot}${sep}`))
 		);