fix(coding-agent): convert clipboard BMP images to PNG on paste

WSL2/WSLg often provides clipboard images as image/bmp only.
Previously this resulted in invalid PNG files being written.

Now readClipboardImage() converts unsupported formats to PNG
via Photon before returning.

Closes #1109

Based on #1112 by @lightningRalf

packages/coding-agent/CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Added `newSession`, `tree`, and `fork` keybinding actions for `/new`, `/tree`, and `/fork` commands. All unbound by default. ([#1114](https://github.com/badlogic/pi-mono/pull/1114) by [@juanibiapina](https://github.com/juanibiapina))
 
+### Fixed
+
+- Fixed clipboard image paste on WSL2/WSLg writing invalid PNG files when clipboard provides `image/bmp` format. BMP images are now converted to PNG before saving. ([#1112](https://github.com/badlogic/pi-mono/pull/1112) by [@lightningRalf](https://github.com/lightningRalf))
+
 ## [0.50.7] - 2026-01-31
 
 ### Fixed

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

@@ -1,12 +1,14 @@
 import Clipboard from "@mariozechner/clipboard";
 import { spawnSync } from "child_process";
 
+import { loadPhoton } from "./photon.js";
+
 export type ClipboardImage = {
 	bytes: Uint8Array;
 	mimeType: string;
 };
 
-const PREFERRED_IMAGE_MIME_TYPES = ["image/png", "image/jpeg", "image/webp", "image/gif"] as const;
+const SUPPORTED_IMAGE_MIME_TYPES = ["image/png", "image/jpeg", "image/webp", "image/gif"] as const;
 
 const DEFAULT_LIST_TIMEOUT_MS = 1000;
 const DEFAULT_READ_TIMEOUT_MS = 3000;
@@ -41,7 +43,7 @@ function selectPreferredImageMimeType(mimeTypes: string[]): string | null {
 		.filter(Boolean)
 		.map((t) => ({ raw: t, base: baseMimeType(t) }));
 
-	for (const preferred of PREFERRED_IMAGE_MIME_TYPES) {
+	for (const preferred of SUPPORTED_IMAGE_MIME_TYPES) {
 		const match = normalized.find((t) => t.base === preferred);
 		if (match) {
 			return match.raw;
@@ -52,6 +54,33 @@ function selectPreferredImageMimeType(mimeTypes: string[]): string | null {
 	return anyImage?.raw ?? null;
 }
 
+function isSupportedImageMimeType(mimeType: string): boolean {
+	const base = baseMimeType(mimeType);
+	return SUPPORTED_IMAGE_MIME_TYPES.some((t) => t === base);
+}
+
+/**
+ * Convert unsupported image formats to PNG using Photon.
+ * Returns null if conversion is unavailable or fails.
+ */
+async function convertToPng(bytes: Uint8Array): Promise<Uint8Array | null> {
+	const photon = await loadPhoton();
+	if (!photon) {
+		return null;
+	}
+
+	try {
+		const image = photon.PhotonImage.new_from_byteslice(bytes);
+		try {
+			return image.get_bytes();
+		} finally {
+			image.free();
+		}
+	} catch {
+		return null;
+	}
+}
+
 function runCommand(
 	command: string,
 	args: string[],
@@ -120,7 +149,7 @@ function readClipboardImageViaXclip(): ClipboardImage | null {
 	}
 
 	const preferred = candidateTypes.length > 0 ? selectPreferredImageMimeType(candidateTypes) : null;
-	const tryTypes = preferred ? [preferred, ...PREFERRED_IMAGE_MIME_TYPES] : [...PREFERRED_IMAGE_MIME_TYPES];
+	const tryTypes = preferred ? [preferred, ...SUPPORTED_IMAGE_MIME_TYPES] : [...SUPPORTED_IMAGE_MIME_TYPES];
 
 	for (const mimeType of tryTypes) {
 		const data = runCommand("xclip", ["-selection", "clipboard", "-t", mimeType, "-o"]);
@@ -139,19 +168,36 @@ export async function readClipboardImage(options?: {
 	const env = options?.env ?? process.env;
 	const platform = options?.platform ?? process.platform;
 
+	let image: ClipboardImage | null = null;
+
 	if (platform === "linux" && isWaylandSession(env)) {
-		return readClipboardImageViaWlPaste() ?? readClipboardImageViaXclip();
+		image = readClipboardImageViaWlPaste() ?? readClipboardImageViaXclip();
+	} else {
+		if (!Clipboard.hasImage()) {
+			return null;
+		}
+
+		const imageData = await Clipboard.getImageBinary();
+		if (!imageData || imageData.length === 0) {
+			return null;
+		}
+
+		const bytes = imageData instanceof Uint8Array ? imageData : Uint8Array.from(imageData);
+		image = { bytes, mimeType: "image/png" };
 	}
 
-	if (!Clipboard.hasImage()) {
+	if (!image) {
 		return null;
 	}
 
-	const imageData = await Clipboard.getImageBinary();
-	if (!imageData || imageData.length === 0) {
-		return null;
+	// Convert unsupported formats (e.g., BMP from WSLg) to PNG
+	if (!isSupportedImageMimeType(image.mimeType)) {
+		const pngBytes = await convertToPng(image.bytes);
+		if (!pngBytes) {
+			return null;
+		}
+		return { bytes: pngBytes, mimeType: "image/png" };
 	}
 
-	const bytes = imageData instanceof Uint8Array ? imageData : Uint8Array.from(imageData);
-	return { bytes, mimeType: "image/png" };
+	return image;
 }

packages/coding-agent/test/clipboard-image-bmp-conversion.test.ts

@@ -0,0 +1,88 @@
+/**
+ * Test for BMP to PNG conversion in clipboard image handling.
+ * Separate from clipboard-image.test.ts due to different mocking requirements.
+ *
+ * This tests the fix for WSL2/WSLg where clipboard often provides image/bmp
+ * instead of image/png.
+ */
+import { describe, expect, test, vi } from "vitest";
+
+function createTinyBmp1x1Red24bpp(): Uint8Array {
+	// Minimal 1x1 24bpp BMP (BGR + row padding to 4 bytes)
+	// File size = 14 (BMP header) + 40 (DIB header) + 4 (pixel row) = 58
+	const buffer = Buffer.alloc(58);
+
+	// BITMAPFILEHEADER
+	buffer.write("BM", 0, "ascii");
+	buffer.writeUInt32LE(buffer.length, 2); // file size
+	buffer.writeUInt16LE(0, 6); // reserved1
+	buffer.writeUInt16LE(0, 8); // reserved2
+	buffer.writeUInt32LE(54, 10); // pixel data offset
+
+	// BITMAPINFOHEADER
+	buffer.writeUInt32LE(40, 14); // DIB header size
+	buffer.writeInt32LE(1, 18); // width
+	buffer.writeInt32LE(1, 22); // height (positive = bottom-up)
+	buffer.writeUInt16LE(1, 26); // planes
+	buffer.writeUInt16LE(24, 28); // bits per pixel
+	buffer.writeUInt32LE(0, 30); // compression (BI_RGB)
+	buffer.writeUInt32LE(4, 34); // image size (incl. padding)
+	buffer.writeInt32LE(0, 38); // x pixels per meter
+	buffer.writeInt32LE(0, 42); // y pixels per meter
+	buffer.writeUInt32LE(0, 46); // colors used
+	buffer.writeUInt32LE(0, 50); // important colors
+
+	// Pixel data (B, G, R) + 1 byte padding
+	buffer[54] = 0x00; // B
+	buffer[55] = 0x00; // G
+	buffer[56] = 0xff; // R
+	buffer[57] = 0x00; // padding
+
+	return new Uint8Array(buffer);
+}
+
+// Mock wl-paste to return BMP
+vi.mock("child_process", async () => {
+	const actual = await vi.importActual<typeof import("child_process")>("child_process");
+	return {
+		...actual,
+		spawnSync: vi.fn((command: string, args: string[]) => {
+			if (command === "wl-paste" && args.includes("--list-types")) {
+				return { status: 0, stdout: Buffer.from("image/bmp\n"), error: null };
+			}
+			if (command === "wl-paste" && args.includes("image/bmp")) {
+				return { status: 0, stdout: Buffer.from(createTinyBmp1x1Red24bpp()), error: null };
+			}
+			return { status: 1, stdout: Buffer.alloc(0), error: null };
+		}),
+	};
+});
+
+// Mock the native clipboard (not used in Wayland path, but needs to be mocked)
+vi.mock("@mariozechner/clipboard", () => ({
+	default: {
+		hasImage: vi.fn(() => false),
+		getImageBinary: vi.fn(() => Promise.resolve(null)),
+	},
+}));
+
+describe("readClipboardImage BMP conversion", () => {
+	test("converts BMP to PNG on Wayland/WSLg", async () => {
+		const { readClipboardImage } = await import("../src/utils/clipboard-image.js");
+
+		// Simulate Wayland session (WSLg)
+		const image = await readClipboardImage({
+			env: { WAYLAND_DISPLAY: "wayland-0" },
+			platform: "linux",
+		});
+
+		expect(image).not.toBeNull();
+		expect(image!.mimeType).toBe("image/png");
+
+		// Verify PNG magic bytes
+		expect(image!.bytes[0]).toBe(0x89);
+		expect(image!.bytes[1]).toBe(0x50); // P
+		expect(image!.bytes[2]).toBe(0x4e); // N
+		expect(image!.bytes[3]).toBe(0x47); // G
+	});
+});