Rapid sensitivity drags triggered a flood of async mask runs; an in-flight
run could settle after the owner pressed Approve and clobber the state, so
the Approve click read a snapshot with overlay:null and early-returned.
Debounce 500ms after the user stops adjusting so the mask settles before any
interaction and the click reads a stable state.
Key the auto-run off a controlKey (sheet:sensitivity) so it fires on mask
entry and on each sheet/sensitivity edit, but never re-fires when approveMask
settles the overlay - preventing both the empty-preview bug and an infinite
settle loop.
The mask screen never populated its overlay: pickCalibration set overlay:null
and the only thing that computed it (approveMask) was gated behind the
Approve button, which is disabled until overlay.slabPx>0 - a chicken-and-egg,
so the preview stayed empty and Approve was permanently disabled. Auto-run
approveMask() whenever the mask screen is active (and on sheet/sensitivity
change) so the overlay and preview render immediately.
The mask screen showed only controls and a pixel-count line - no photo, so
the owner had nothing to adjust the sheet/sensitivity against. Draw the
calibration photo to a canvas and paint removed (non-slab) pixels as a
light-gray checkerboard (CAPTURE-45/50), redrawing when the overlay settles.
Verified in Chromium: mask step now shows the photo with the checkerboard.
`session.state` is a Svelte store; `$: state = session.state` bound the store
object (not its value), so state.capture was undefined and cap.k threw on
mount. Bind a local const to the store and use the $ prefix ($stateStore),
and use get() in App.onPhotosReady. Verified in Chromium: hero -> batch ->
sample uploads show thumbs.
`createCaptureSession()` returns {state: Store, ...}; Svelte's $ prefix
calls .subscribe on the object, not the store, so $captureSession.state
threw 'subscribe is not a function' on App mount → black page. Reference the
store directly (auto-subscribes): captureSession.state / session.state /
session.lineup(). Verified: tsc clean, build green, 150/150 tests, and the
live app renders in Chromium.
Ty