fix(R): detect Windows ARM using IsWow64Process2 API

Deno.build.arch reports x86_64 even when x64 Deno runs on ARM64 hardware
under emulation. Use Windows IsWow64Process2 API via FFI to detect the
actual native hardware architecture.

This fixes the x64-on-ARM detection so the custom error message displays
instead of the generic "Please check your installation of R" message.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: cderv

src/core/knitr.ts

@@ -12,6 +12,7 @@ import { readYamlFromString } from "./yaml.ts";
 import { coerce, satisfies } from "semver/mod.ts";
 import { debug } from "../deno_ral/log.ts";
 import { isWindows } from "../deno_ral/platform.ts";
+import { isWindowsArm } from "./windows.ts";
 
 export interface KnitrCapabilities {
   versionMajor: number;
@@ -79,10 +80,9 @@ export class WindowsArmX64RError extends Error {
 function checkWindowsArmR(platform: string | undefined): void {
   if (!platform) return;
 
-  const isWindowsArm = isWindows && Deno.build.arch === "aarch64";
   const isX64R = platform.includes("x86_64") || platform.includes("i386");
 
-  if (isWindowsArm && isX64R) {
+  if (isWindowsArm() && isX64R) {
     throw new WindowsArmX64RError(
       "x64 R detected on Windows ARM.\n\n" +
         "x64 R runs under emulation and is not reliable for Quarto.\n" +

src/core/windows.ts

@@ -163,3 +163,53 @@ export async function safeWindowsExec(
     removeIfExists(tempFile);
   }
 }
+
+// Detect Windows ARM hardware using IsWow64Process2 API
+// Returns true if running on ARM64 hardware (even from x64 Deno under emulation)
+export function isWindowsArm(): boolean {
+  if (!isWindows) {
+    return false;
+  }
+
+  try {
+    // Load kernel32.dll
+    const kernel32 = Deno.dlopen("kernel32.dll", {
+      IsWow64Process2: {
+        parameters: ["pointer", "pointer", "pointer"],
+        result: "i32",
+      },
+      GetCurrentProcess: {
+        parameters: [],
+        result: "pointer",
+      },
+    });
+
+    // Get current process handle
+    const hProcess = kernel32.symbols.GetCurrentProcess();
+
+    // Prepare output parameters - allocate buffer for USHORT (2 bytes each)
+    const processMachineBuffer = new Uint16Array(1);
+    const nativeMachineBuffer = new Uint16Array(1);
+
+    // Call IsWow64Process2 with pointers to buffers
+    const result = kernel32.symbols.IsWow64Process2(
+      hProcess,
+      Deno.UnsafePointer.of(processMachineBuffer),
+      Deno.UnsafePointer.of(nativeMachineBuffer),
+    );
+
+    kernel32.close();
+
+    if (result === 0) {
+      // Function failed
+      return false;
+    }
+
+    // IMAGE_FILE_MACHINE_ARM64 = 0xAA64 = 43620
+    const IMAGE_FILE_MACHINE_ARM64 = 0xAA64;
+    return nativeMachineBuffer[0] === IMAGE_FILE_MACHINE_ARM64;
+  } catch {
+    // IsWow64Process2 not available (Windows < 10) or other error
+    return false;
+  }
+}