feat(device): use WebP for device screenshot producers

[quanruzhuoxiu]

Summary

• route Android ADB, iOS WDA, macOS, and Windows PNG captures through the shared canonical WebP encoder
• encode Android scrcpy H.264 frames as WebP through its dedicated FFmpeg-to-Sharp pipeline
• preserve native JPEG streams where another lossy conversion would add cost and reduce fidelity
• retain the desktop smoke-test stability changes in this final downstream PR
• update Android, iOS, Computer, Windows, and RDP regression coverage

The reusable PNG/JPEG-to-WebP implementation lives in packages/shared/src/img/transform.ts: canonicalizeScreenshotBase64() validates the actual image bytes and calls convertImgBufferToWebp(), which uses Sharp.webp({ quality: 90, effort: 1 }) in Node. Device adapters call this shared boundary unless the source already provides a JPEG stream that should be preserved.

WebP generation paths

Scenario	Source format	Where WebP is generated
Android ADB	PNG	packages/android/src/device.ts calls shared canonicalizeScreenshotBase64(), which encodes with Sharp
Android scrcpy	H.264 keyframe	packages/android/src/scrcpy-manager.ts decodes H.264 to raw RGB with FFmpeg, then encodes once with Sharp.webp({ quality: 90, effort: 1 })
iOS WDA screenshot	PNG	packages/ios/src/device.ts calls shared canonicalizeScreenshotBase64(), which encodes with Sharp
macOS desktop	PNG	packages/computer/src/device.ts calls shared canonicalizeScreenshotBase64(), which encodes with Sharp
Windows desktop	PNG	packages/computer/src/device.ts calls shared canonicalizeScreenshotBase64(), which encodes with Sharp
RDP	JPEG or PNG, depending on backend	packages/computer/src/rdp/device.ts uses preserveJpeg: true: JPEG remains byte-for-byte JPEG, while PNG is encoded as WebP
iOS MJPEG frame source	JPEG	No WebP encoding; native JPEG frames pass through to avoid a second lossy encode

Stack

• Depends on feat(report): support WebP screenshot consumers #2857
• Replaces the clean-stack role of feat(device): use WebP for device screenshot producers #2853
• feat(device): use WebP for device screenshot producers #2853 remains unchanged as a rollback option
• Stability-only changes are intentionally isolated in this downstream device PR

Validation

• pnpm exec nx run-many -t build -p @midscene/android @midscene/ios @midscene/computer
• pnpm --filter @midscene/android test (16 files, 325 tests passed)
• pnpm --filter @midscene/ios test (12 files, 146 tests passed)
• pnpm --filter @midscene/computer test (13 files, 89 tests passed)
• pnpm run type-check:tests
• pnpm run lint

[quanruzhuoxiu]

Closing this superseded WebP stack PR. The replacement stack is #3012 → #3013 → #3014 and incorporates the latest main branch plus the follow-up architecture, format-validation, and CI fixes. PR #2856 remains open because it is an independent model-input evidence change.