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/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
+	});
+});