fix(R): display WindowsArmX64RError in quarto check

Catch WindowsArmX64RError in knitrCb before withSpinner can swallow it,
then display the custom error message instead of the generic message.

This ensures users see the helpful x64-on-ARM error with download links
instead of "Please check your installation of R."

Author: cderv

src/execute/rmd.ts

@@ -26,6 +26,7 @@ import {
   knitrCapabilitiesMessage,
   knitrInstallationMessage,
   rInstallationMessage,
+  WindowsArmX64RError,
 } from "../core/knitr.ts";
 import {
   DependenciesOptions,
@@ -139,13 +140,23 @@ title: "Title"
     const kMessage = "Checking R installation...........";
     let caps: KnitrCapabilities | undefined;
     let rBin: string | undefined;
+    let x64ArmError: WindowsArmX64RError | undefined;
     const json: Record<string, unknown> = {};
     if (conf.jsonResult) {
       (conf.jsonResult.tools as Record<string, unknown>).knitr = json;
     }
     const knitrCb = async () => {
       rBin = await checkRBinary();
-      caps = await knitrCapabilities(rBin);
+      try {
+        caps = await knitrCapabilities(rBin);
+      } catch (e) {
+        if (e instanceof WindowsArmX64RError) {
+          x64ArmError = e;
+          // Don't rethrow - let caps stay undefined but capture error
+        } else {
+          throw e; // Rethrow other errors
+        }
+      }
     };
     if (conf.jsonResult) {
       await knitrCb();
@@ -205,6 +216,16 @@ title: "Title"
       checkInfoMsg(msg);
       json["installed"] = false;
       checkInfoMsg("");
+    } else if (x64ArmError) {
+      // x64 R on Windows ARM detected - show specific error
+      json["installed"] = false;
+      checkCompleteMessage(kMessage + "(None)\n");
+      const errorLines = x64ArmError.message.split("\n");
+      errorLines.forEach((line) => {
+        checkInfoMsg(line);
+      });
+      json["error"] = x64ArmError.message;
+      checkInfoMsg("");
     } else if (caps === undefined) {
       json["installed"] = false;
       checkCompleteMessage(kMessage + "(None)\n");