Unit 2 of slimming the mandatory read. Verbatim move again - the four capture
blocks leave ai.md unchanged in content, and one stub carries the law.
- docs/ai/capture.md: 'Screen backdrop capture', 'Webcam capture', 'Webcam
background effects' and 'Vertical (9:16) tier camera placement', byte-
identical, grouped under backdrop / webcam / vertical headings, with a
'Related in ai.md' footer.
- ai.md stub keeps: the locked-Background model and NormalizeBackgrounds;
ActiveBackgroundImage is fed by static art only (2026-08-23 regression);
window:/picker: keys are session-scoped and a live pin beats auto-detect;
the settled WinRT interop paths (TryGetDataUnsafe, from-DXGIDevice); the
VideoFrame seam, own-catch subtype ladder and no fallback camera; one app-
level webcam identity with live-lock attainability; CameraManager as the one
effects processing point with per-session mask smoothing; geometry-only
vertical tier and the model-level rect lock.
- docs/ai/index.md gains the capture.md row; Services/index.md (2) and
TASKS/task-38-window-backdrop.md repointed.
ai.md 1,975 -> 1,558 lines. No source touched; no push.
