Guard .exe extraction to Windows and improve error diagnostics

Only attempt self-extracting .exe on Windows in unzip().
Include candidate filenames in TinyTeX download error for easier
debugging when naming drift occurs.

Author: cderv

src/core/zip.ts

@@ -12,7 +12,7 @@ import { safeWindowsExec } from "./windows.ts";
 export function unzip(file: string, dir?: string) {
   if (!dir) dir = dirname(file);
 
-  if (file.endsWith(".exe")) {
+  if (isWindows && file.endsWith(".exe")) {
     // Self-extracting 7z archive (e.g., TinyTeX-windows.exe)
     return safeWindowsExec(
       file,

src/tools/impl/tinytex.ts

@@ -160,7 +160,10 @@ async function preparePackage(
     await context.download(`TinyTex ${version}`, result.url, filePath);
     return { filePath, version };
   } else {
-    context.error("Couldn't determine what URL to use to download");
+    context.error(
+      `Couldn't determine what URL to use to download TinyTeX. ` +
+        `Tried: ${candidates.join(", ")}`,
+    );
     return Promise.reject();
   }
 }