feat(ai): image-preprocess mit sharp (Resize + JPEG + EXIF-Strip)

tests/unit/image-preprocess.test.ts

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+import { describe, it, expect } from 'vitest';
+import sharp from 'sharp';
+import { preprocessImage } from '../../src/lib/server/ai/image-preprocess';
+
+async function makeTestImage(
+  width: number,
+  height: number,
+  format: 'jpeg' | 'png' | 'webp' = 'jpeg'
+): Promise<Buffer> {
+  return sharp({
+    create: {
+      width,
+      height,
+      channels: 3,
+      background: { r: 128, g: 128, b: 128 }
+    }
+  })
+    .toFormat(format)
+    .toBuffer();
+}
+
+describe('preprocessImage', () => {
+  it('resizes a landscape image so long edge <= 1600px', async () => {
+    const input = await makeTestImage(4000, 2000);
+    const { buffer, mimeType } = await preprocessImage(input);
+    const meta = await sharp(buffer).metadata();
+    expect(Math.max(meta.width ?? 0, meta.height ?? 0)).toBeLessThanOrEqual(1600);
+    expect(Math.max(meta.width ?? 0, meta.height ?? 0)).toBeGreaterThan(1000);
+    expect(mimeType).toBe('image/jpeg');
+  });
+
+  it('resizes a portrait image so long edge <= 1600px', async () => {
+    const input = await makeTestImage(2000, 4000);
+    const { buffer } = await preprocessImage(input);
+    const meta = await sharp(buffer).metadata();
+    expect(Math.max(meta.width ?? 0, meta.height ?? 0)).toBeLessThanOrEqual(1600);
+  });
+
+  it('does not upscale smaller images', async () => {
+    const input = await makeTestImage(800, 600);
+    const { buffer } = await preprocessImage(input);
+    const meta = await sharp(buffer).metadata();
+    expect(meta.width).toBe(800);
+    expect(meta.height).toBe(600);
+  });
+
+  it('converts PNG input to JPEG output', async () => {
+    const input = await makeTestImage(1000, 1000, 'png');
+    const { buffer, mimeType } = await preprocessImage(input);
+    const meta = await sharp(buffer).metadata();
+    expect(meta.format).toBe('jpeg');
+    expect(mimeType).toBe('image/jpeg');
+  });
+
+  it('strips EXIF metadata', async () => {
+    const input = await sharp({
+      create: { width: 100, height: 100, channels: 3, background: '#888' }
+    })
+      .withMetadata({ exif: { IFD0: { Copyright: 'test' } } })
+      .jpeg()
+      .toBuffer();
+    const { buffer } = await preprocessImage(input);
+    const meta = await sharp(buffer).metadata();
+    expect(meta.exif).toBeUndefined();
+  });
+
+  it('rejects non-image buffers', async () => {
+    const notAnImage = Buffer.from('hello world');
+    await expect(preprocessImage(notAnImage)).rejects.toThrow();
+  });
+});