Polish Feynman harness and stabilize Pi web runtime

src/system/executables.ts

@@ -0,0 +1,46 @@
+import { spawnSync } from "node:child_process";
+import { existsSync } from "node:fs";
+
+export const PANDOC_FALLBACK_PATHS = [
+	"/opt/homebrew/bin/pandoc",
+	"/usr/local/bin/pandoc",
+];
+
+export const BREW_FALLBACK_PATHS = [
+	"/opt/homebrew/bin/brew",
+	"/usr/local/bin/brew",
+];
+
+export const BROWSER_FALLBACK_PATHS = [
+	"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+	"/Applications/Chromium.app/Contents/MacOS/Chromium",
+	"/Applications/Brave Browser.app/Contents/MacOS/Brave Browser",
+	"/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge",
+];
+
+export const MERMAID_FALLBACK_PATHS = [
+	"/opt/homebrew/bin/mmdc",
+	"/usr/local/bin/mmdc",
+];
+
+export function resolveExecutable(name: string, fallbackPaths: string[] = []): string | undefined {
+	for (const candidate of fallbackPaths) {
+		if (existsSync(candidate)) {
+			return candidate;
+		}
+	}
+
+	const result = spawnSync("sh", ["-lc", `command -v ${name}`], {
+		encoding: "utf8",
+		stdio: ["ignore", "pipe", "ignore"],
+	});
+
+	if (result.status === 0) {
+		const resolved = result.stdout.trim();
+		if (resolved) {
+			return resolved;
+		}
+	}
+
+	return undefined;
+}

src/system/promise-polyfill.ts

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+type PromiseWithResolvers<T> = {
+	promise: Promise<T>;
+	resolve: (value: T | PromiseLike<T>) => void;
+	reject: (reason?: unknown) => void;
+};
+
+declare global {
+	interface PromiseConstructor {
+		withResolvers?<T>(): PromiseWithResolvers<T>;
+	}
+}
+
+if (typeof Promise.withResolvers !== "function") {
+	Promise.withResolvers = function withResolvers<T>(): PromiseWithResolvers<T> {
+		let resolve!: (value: T | PromiseLike<T>) => void;
+		let reject!: (reason?: unknown) => void;
+		const promise = new Promise<T>((res, rej) => {
+			resolve = res;
+			reject = rej;
+		});
+		return { promise, resolve, reject };
+	};
+}
+
+export {};
+