Fix non-PNG images not displaying in Kitty protocol terminals

JPEG/GIF/WebP images were not rendering in terminals using the Kitty
graphics protocol (Kitty, Ghostty, WezTerm) because it requires PNG
format (f=100). Non-PNG images are now converted to PNG using sharp
before being sent to the terminal.

packages/coding-agent/src/utils/image-convert.ts

@@ -0,0 +1,26 @@
+/**
+ * Convert image to PNG format for terminal display.
+ * Kitty graphics protocol requires PNG format (f=100).
+ */
+export async function convertToPng(
+	base64Data: string,
+	mimeType: string,
+): Promise<{ data: string; mimeType: string } | null> {
+	// Already PNG, no conversion needed
+	if (mimeType === "image/png") {
+		return { data: base64Data, mimeType };
+	}
+
+	try {
+		const sharp = (await import("sharp")).default;
+		const buffer = Buffer.from(base64Data, "base64");
+		const pngBuffer = await sharp(buffer).png().toBuffer();
+		return {
+			data: pngBuffer.toString("base64"),
+			mimeType: "image/png",
+		};
+	} catch {
+		// Sharp not available or conversion failed
+		return null;
+	}
+}