Function attachC2PAIfEnabled

server/src/services/illustration-generator.ts:198–241

(
  result: { imageBuffer: Buffer; promptUsed: string },
  manifest: { title: string; category?: string; editionDate?: string },
)

 * via notifySystemError) so sustained failures surface rather than hiding in logs.
 */
export async function attachC2PAIfEnabled(
  result: { imageBuffer: Buffer; promptUsed: string },
  manifest: { title: string; category?: string; editionDate?: string },
): Promise<GenerateIllustrationResult> {
  if (!isC2PASigningEnabled()) return result;
  try {
    // Re-encode to PNG before signing. Gemini's image model sometimes returns
    // WebP/JPEG variants that c2pa-node rejects with "type is unsupported";
    // normalizing through sharp guarantees the bytes match the image/png
    // mimeType declared to the signer and matches what the portrait path does.
    // failOn:'error' + .rotate() apply EXIF orientation and drop any upstream
    // metadata so the C2PA manifest is the sole provenance source of truth.
    const pngBuffer = await sharp(result.imageBuffer, { failOn: 'error' })
      .rotate()
      .png()
      .toBuffer();
    const signed = signC2PA(pngBuffer, {
      claimGenerator: 'AAO Illustration Generator',
      title: manifest.title,
      softwareAgent: { name: GEMINI_IMAGE_MODEL, version: GEMINI_IMAGE_VERSION },
      attributes: {
        ...(manifest.category ? { category: manifest.category } : {}),
        ...(manifest.editionDate ? { edition_date: manifest.editionDate } : {}),
        prompt_sha256: createHash('sha256').update(result.promptUsed).digest('hex'),
      },
    });
    return {
      imageBuffer: signed.signedBuffer,
      promptUsed: result.promptUsed,
      c2pa: { signedAt: new Date(), manifestDigest: signed.manifestDigest },
    };
  } catch (err) {
    const errorMessage = err instanceof Error ? err.message : String(err);
    logger.error({ err, title: manifest.title }, 'C2PA signing failed');
    notifySystemError({
      source: 'c2pa-illustration-signing',
      errorMessage: `Illustration signing failed for "${manifest.title}": ${errorMessage}`,
    });
    if (process.env.C2PA_STRICT === 'true') {
      throw err;
    }
    return result;
  }
}