Add conversation image replacement

tests/image-replacement.test.ts

@@ -0,0 +1,35 @@
+import sharp from 'sharp';
+import { describe, expect, it } from 'vitest';
+import { ImageReplacementInputError, replaceGreenScreen } from '../src/services/image-replacement.js';
+
+describe('replaceGreenScreen', () => {
+  it('warps a replacement into the detected green region and preserves the surrounding source', async () => {
+    const source = await sharp({
+      create: { width: 200, height: 160, channels: 3, background: '#20252a' },
+    }).composite([{ input: Buffer.from(
+      '<svg width="200" height="160"><polygon points="45,30 165,42 150,135 35,120" fill="#00ff00"/></svg>',
+    ) }]).png().toBuffer();
+    const target = await sharp({
+      create: { width: 80, height: 120, channels: 3, background: '#ee2233' },
+    }).png().toBuffer();
+
+    const result = await replaceGreenScreen(source, target);
+    const decoded = await sharp(result.bytes).raw().toBuffer({ resolveWithObject: true });
+    const pixel = (x: number, y: number) => {
+      const offset = (y * decoded.info.width + x) * decoded.info.channels;
+      return [...decoded.data.subarray(offset, offset + 3)];
+    };
+
+    expect(result).toMatchObject({ mimeType: 'image/jpeg', width: 200, height: 160 });
+    expect(pixel(100, 80)[0]).toBeGreaterThan(150);
+    expect(pixel(100, 80)[1]).toBeLessThan(100);
+    expect(pixel(10, 10)[0]).toBeLessThan(70);
+  });
+
+  it('rejects a source without a usable green-screen area', async () => {
+    const source = await sharp({ create: { width: 100, height: 100, channels: 3, background: '#223344' } }).png().toBuffer();
+    const target = await sharp({ create: { width: 20, height: 20, channels: 3, background: '#ffffff' } }).png().toBuffer();
+
+    await expect(replaceGreenScreen(source, target)).rejects.toThrow(ImageReplacementInputError);
+  });
+});