Problem

PNG images with transparency were being converted to JPEG format when sent via the message tool to Discord, which strips the alpha channel and loses transparency.

Solution

Detect PNG images that have an alpha channel and use PNG optimization instead of JPEG compression, preserving the transparency.

Changes

• Added hasAlphaChannel() function to detect PNG files with alpha channel
• Added resizeToPng() function for PNG-specific image resizing
• Added optimizeImageToPng() function to preserve PNG transparency
• Modified src/web/media.ts to detect PNG with alpha and route to PNG optimization

Fixes #1473

🤖 AI-Assisted Development

Tool: Claude (Opus 4.5) via Clawdbot

Testing: Lightly tested

• tsc --noEmit passes ✅
• No runtime tests yet

Prompts/Session:
User asked to fix issue #1473. After analyzing the codebase:

1. Found loadWebMedia() in src/web/media.ts routes all images through optimizeImageToJpeg()
2. JPEG doesn't support alpha → transparency lost
3. Solution: detect PNG+alpha via sharp metadata, route to new PNG optimizer

Understanding: Yes ✅

• hasAlphaChannel(): Uses sharp's metadata().hasAlpha or channels === 4 to detect transparency
• resizeToPng(): Resizes with .png({ compressionLevel }) instead of .jpeg()
• optimizeImageToPng(): Grid search over sizes/compression levels (like JPEG version)
• Integration: Check isPng && hasAlpha before optimization, route accordingly