fix(pi-dosbox): include QBasic files in jsdos bundle

The previous approach of writing files to Emscripten FS after DOSBox
started didn't work because the C: drive mount was pointing elsewhere.

Now we create a proper zip archive of QBasic files and include it in
the jsdos bundle using the extract() API with a data URL. The bundle
extracts to the C: drive root on startup.

packages/coding-agent/examples/extensions/pi-dosbox/src/dosbox-instance.ts

@@ -79,8 +79,7 @@ export class DosboxInstance {
 			const bundle = await this.createBundle(emu);
 			this.ci = await emu.dosboxDirect(bundle);
 
-			// Mount QBasic files to C:
-			await this.mountQBasic();
+			// QBasic files are included in the bundle, no post-init mount needed
 
 			const events = this.ci.events();
 
@@ -121,54 +120,120 @@ export class DosboxInstance {
 
 	private async createBundle(emu: Emulators): Promise<Uint8Array> {
 		const bundle = await emu.bundle();
+
+		// Add QBasic files to the bundle
+		// We'll create a zip and include it
+		await this.addQBasicToBundle(bundle);
+
+		// Set up autoexec to show what's available
 		bundle.autoexec(
 			"@echo off",
-			"mount c c:",
 			"c:",
 			"cls",
-			"echo QuickBASIC 4.5 mounted at C:\\QB",
+			"echo QuickBASIC 4.5 is at C:\\QB",
+			"echo.",
+			"echo Type: CD QB",
+			"echo Then: QB.EXE",
 			"echo.",
-			"dir /w",
 		);
+
 		return bundle.toUint8Array(true);
 	}
 
-	private async mountQBasic(): Promise<void> {
-		if (!this.ci) return;
-
-		const fs = (this.ci as unknown as { transport: { module: { FS: EmscriptenFS } } }).transport.module.FS;
-		const rescan = (this.ci as unknown as { transport: { module: { _rescanFilesystem: () => void } } }).transport
-			.module._rescanFilesystem;
-
-		// Create directory structure
-		try {
-			fs.mkdir("/c");
-		} catch {
-			/* exists */
-		}
-		try {
-			fs.mkdir("/c/QB");
-		} catch {
-			/* exists */
-		}
-
-		// Read QBasic files from the extension directory
+	private async addQBasicToBundle(bundle: Awaited<ReturnType<Emulators["bundle"]>>): Promise<void> {
+		// Read QBasic files and create a zip data URL
 		const qbasicDir = join(__dirname, "..", "qbasic");
 		const { readdirSync, readFileSync } = await import("node:fs");
 
-		const files = readdirSync(qbasicDir);
+		const files = readdirSync(qbasicDir).filter((f) => !f.startsWith("."));
+
+		// Create a simple zip structure
+		const zipParts: Buffer[] = [];
+		const centralDir: Buffer[] = [];
+		let offset = 0;
+
 		for (const file of files) {
-			if (file.startsWith(".")) continue;
-			try {
-				const data = readFileSync(join(qbasicDir, file));
-				fs.writeFile(`/c/QB/${file.toUpperCase()}`, data);
-			} catch (e) {
-				console.error(`Failed to mount ${file}:`, e);
-			}
+			const data = readFileSync(join(qbasicDir, file));
+			const fileName = `QB/${file.toUpperCase()}`;
+			const fileNameBuf = Buffer.from(fileName, "utf-8");
+
+			// Local file header
+			const localHeader = Buffer.alloc(30 + fileNameBuf.length);
+			localHeader.writeUInt32LE(0x04034b50, 0); // signature
+			localHeader.writeUInt16LE(20, 4); // version needed
+			localHeader.writeUInt16LE(0, 6); // flags
+			localHeader.writeUInt16LE(0, 8); // compression (none)
+			localHeader.writeUInt16LE(0, 10); // mod time
+			localHeader.writeUInt16LE(0, 12); // mod date
+			localHeader.writeUInt32LE(this.crc32Buf(data), 14); // crc32
+			localHeader.writeUInt32LE(data.length, 18); // compressed size
+			localHeader.writeUInt32LE(data.length, 22); // uncompressed size
+			localHeader.writeUInt16LE(fileNameBuf.length, 26); // filename length
+			localHeader.writeUInt16LE(0, 28); // extra field length
+			fileNameBuf.copy(localHeader, 30);
+
+			zipParts.push(localHeader);
+			zipParts.push(data);
+
+			// Central directory entry
+			const cdEntry = Buffer.alloc(46 + fileNameBuf.length);
+			cdEntry.writeUInt32LE(0x02014b50, 0); // signature
+			cdEntry.writeUInt16LE(20, 4); // version made by
+			cdEntry.writeUInt16LE(20, 6); // version needed
+			cdEntry.writeUInt16LE(0, 8); // flags
+			cdEntry.writeUInt16LE(0, 10); // compression
+			cdEntry.writeUInt16LE(0, 12); // mod time
+			cdEntry.writeUInt16LE(0, 14); // mod date
+			cdEntry.writeUInt32LE(this.crc32Buf(data), 16); // crc32
+			cdEntry.writeUInt32LE(data.length, 20); // compressed size
+			cdEntry.writeUInt32LE(data.length, 24); // uncompressed size
+			cdEntry.writeUInt16LE(fileNameBuf.length, 28); // filename length
+			cdEntry.writeUInt16LE(0, 30); // extra field length
+			cdEntry.writeUInt16LE(0, 32); // comment length
+			cdEntry.writeUInt16LE(0, 34); // disk number start
+			cdEntry.writeUInt16LE(0, 36); // internal attrs
+			cdEntry.writeUInt32LE(0, 38); // external attrs
+			cdEntry.writeUInt32LE(offset, 42); // relative offset
+			fileNameBuf.copy(cdEntry, 46);
+
+			centralDir.push(cdEntry);
+			offset += localHeader.length + data.length;
 		}
 
-		// Rescan so DOS sees the new files
-		rescan();
+		const cdOffset = offset;
+		const cdSize = centralDir.reduce((sum, buf) => sum + buf.length, 0);
+
+		// End of central directory
+		const eocd = Buffer.alloc(22);
+		eocd.writeUInt32LE(0x06054b50, 0); // signature
+		eocd.writeUInt16LE(0, 4); // disk number
+		eocd.writeUInt16LE(0, 6); // disk with CD
+		eocd.writeUInt16LE(files.length, 8); // entries on disk
+		eocd.writeUInt16LE(files.length, 10); // total entries
+		eocd.writeUInt32LE(cdSize, 12); // CD size
+		eocd.writeUInt32LE(cdOffset, 16); // CD offset
+		eocd.writeUInt16LE(0, 20); // comment length
+
+		const zipBuffer = Buffer.concat([...zipParts, ...centralDir, eocd]);
+		const base64 = zipBuffer.toString("base64");
+		const dataUrl = `data:application/zip;base64,${base64}`;
+
+		// Extract to root of C: drive
+		bundle.extract(dataUrl, "/", "zip");
+	}
+
+	private crc32Buf(buffer: Buffer): number {
+		let crc = 0xffffffff;
+		for (const byte of buffer) {
+			crc = CRC_TABLE[(crc ^ byte) & 0xff] ^ (crc >>> 8);
+		}
+		return (crc ^ 0xffffffff) >>> 0;
+	}
+
+	// No longer needed - files are in bundle
+	// biome-ignore lint/correctness/noUnusedPrivateClassMembers: Keeping for reference
+	private async mountQBasicPostInit(): Promise<void> {
+		// This approach didn't work - keeping for reference
 	}
 
 	private expandRgbToRgba(rgb: Uint8Array): Uint8Array {
@@ -417,12 +482,3 @@ function createCrcTable(): Uint32Array {
 	}
 	return table;
 }
-
-// Emscripten FS type
-interface EmscriptenFS {
-	mkdir(path: string): void;
-	writeFile(path: string, data: Uint8Array | Buffer): void;
-	readFile(path: string): Uint8Array;
-	readdir(path: string): string[];
-	unlink(path: string): void;
-}