WIP: run Frame Control on Linux and Windows

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/build/fetch-python.js

@@ -0,0 +1,48 @@
+// Downloads the official Windows embeddable Python into build/python-win, which
+// the Windows build bundles as resources/python (so Windows users need no Python).
+// Pinned by version and SHA-256. Run: node build/fetch-python.js
+const crypto = require("crypto");
+const fs = require("fs");
+const https = require("https");
+const path = require("path");
+const { execFileSync } = require("child_process");
+
+const VERSION = "3.12.10";
+const SHA256 = "4acbed6dd1c744b0376e3b1cf57ce906f9dc9e95e68824584c8099a63025a3c3";
+const URL = `https://www.python.org/ftp/python/${VERSION}/python-${VERSION}-embed-amd64.zip`;
+const OUT = path.join(__dirname, "python-win");
+
+function get(url) {
+  return new Promise((resolve, reject) => {
+    https.get(url, (res) => {
+      if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
+        res.resume();
+        return resolve(get(res.headers.location));
+      }
+      if (res.statusCode !== 200) return reject(new Error(`${url}: HTTP ${res.statusCode}`));
+      const chunks = [];
+      res.on("data", (c) => chunks.push(c));
+      res.on("end", () => resolve(Buffer.concat(chunks)));
+    }).on("error", reject);
+  });
+}
+
+(async () => {
+  if (fs.existsSync(path.join(OUT, "python.exe")) && fs.readFileSync(path.join(OUT, ".version"), "utf8") === VERSION) {
+    console.log(`Python ${VERSION} already in ${OUT}`);
+    return;
+  }
+  const zip = await get(URL);
+  const sum = crypto.createHash("sha256").update(zip).digest("hex");
+  if (sum !== SHA256) throw new Error(`checksum mismatch for ${URL}: ${sum}`);
+  fs.rmSync(OUT, { recursive: true, force: true });
+  fs.mkdirSync(OUT, { recursive: true });
+  const file = path.join(OUT, "python.zip");
+  fs.writeFileSync(file, zip);
+  // bsdtar (macOS, Windows 10+) reads zip files; GNU tar doesn't, so fall back to unzip.
+  try { execFileSync("tar", ["-xf", file, "-C", OUT]); }
+  catch { execFileSync("unzip", ["-q", "-o", file, "-d", OUT]); }
+  fs.rmSync(file);
+  fs.writeFileSync(path.join(OUT, ".version"), VERSION);
+  console.log(`Python ${VERSION} -> ${OUT}`);
+})().catch((e) => { console.error(e.message); process.exit(1); });