fix(coding-agent): process BMP images from disk

closes #6047

packages/coding-agent/test/tools.test.ts

@@ -34,6 +34,22 @@ function getTextOutput(result: any): string {
 	);
 }
 
+function createTinyBmp1x1Red24bpp(): Buffer {
+	const buffer = Buffer.alloc(58);
+	buffer.write("BM", 0, "ascii");
+	buffer.writeUInt32LE(buffer.length, 2);
+	buffer.writeUInt32LE(54, 10);
+	buffer.writeUInt32LE(40, 14);
+	buffer.writeInt32LE(1, 18);
+	buffer.writeInt32LE(1, 22);
+	buffer.writeUInt16LE(1, 26);
+	buffer.writeUInt16LE(24, 28);
+	buffer.writeUInt32LE(0, 30);
+	buffer.writeUInt32LE(4, 34);
+	buffer[56] = 0xff;
+	return buffer;
+}
+
 describe("Coding Agent Tools", () => {
 	let testDir: string;
 
@@ -191,6 +207,24 @@ describe("Coding Agent Tools", () => {
 			expect((imageBlock?.data ?? "").length).toBeGreaterThan(0);
 		});
 
+		it("should read BMP files from disk as PNG image attachments", async () => {
+			const testFile = join(testDir, "image.bmp");
+			writeFileSync(testFile, createTinyBmp1x1Red24bpp());
+
+			const result = await readTool.execute("test-call-img-bmp", { path: testFile });
+
+			expect(result.content[0]?.type).toBe("text");
+			expect(getTextOutput(result)).toContain("Read image file [image/png]");
+			expect(getTextOutput(result)).toContain("[Image converted from image/bmp to image/png.]");
+
+			const imageBlock = result.content.find(
+				(c): c is { type: "image"; mimeType: string; data: string } => c.type === "image",
+			);
+			expect(imageBlock).toBeDefined();
+			expect(imageBlock?.mimeType).toBe("image/png");
+			expect(Buffer.from(imageBlock?.data ?? "", "base64")[0]).toBe(0x89);
+		});
+
 		it("should treat files with image extension but non-image content as text", async () => {
 			const testFile = join(testDir, "not-an-image.png");
 			writeFileSync(testFile, "definitely not a png");