Cryptomatte: the Selection tool picks IDs while the effect is selected

As in After Effects, with the Cryptomatte effect selected in Effect Controls and the
Selection tool active, a click on its layer in the Composition viewer picks the ID
under the cursor without arming the eyedropper: plain replaces, Shift adds, Alt or
Ctrl removes, one undo step each, with the same hover name and highlight. A drag
there moves nothing.

The viewer keeps its clicks off the layer, on its own handles there (bounding box,
gizmo, mask vertices, motion-path keys, guides, region of interest), while a region
of interest or Free Transform box is drawn, with another effect or a property row
selected, and with other tools. A press in the pass the pointer leaves the layer is
passed on to the viewer as a click. Reuses the eyedropper's code path
(effect.pickCryptomatte); automation id viewer.cryptoSelect.

Fixes #2839

docs/control-protocol.md

@@ -152,7 +152,9 @@ revolutions are `timeline.prop.<uid>.revolutions`, `effectControls.prop.<uid>.re
 `viewer.motionPath.<layer>.<key>[.in|.out]`, `viewer.puppetPin.<uid>[.rotate|.scale]`,
 `viewer.freeTransform.handle.<i>`, `viewer.cryptoPick` (the Cryptomatte eyedropper's hover chip; its
 label is the chip's text), `viewer.cryptoPick.error` (the chip when it shows an error; label `whole`, or
-`cut` when the message is cut off), `viewer.cryptoPick.highlight` (the hovered ID's highlighted area) and
+`cut` when the message is cut off), `viewer.cryptoPick.highlight` (the hovered ID's highlighted area),
+`viewer.cryptoSelect` (the Selection tool picking Cryptomatte IDs over the layer while its Cryptomatte
+effect is selected in Effect Controls, no eyedropper armed; label: the Selection's name) and
 `viewer.regionOfInterest`; the Graph Editor adds `timeline.graph.transformBox[.<i>]`,
 `timeline.graph.snap` and `timeline.graph.reference`. Use `ui.elements` to see what is on screen.
 

docs/effects-parity.md

@@ -26,7 +26,7 @@ corpus compares renders, each effect is assumed to differ somewhere, and users k
 
 | Category | Effects | On the GPU | Known differences or bugs |
 |---|---:|---:|---|
-| 3D Channel | 8 | 8 | Cryptomatte's GPU path is slow (#473; the Selection is picked in the viewer with an eyedropper, quoted names with commas fixed); multi-layer EXR: one decode per frame for the picture and the channels, cache softly bounded at 1 GB (#474; holding channels as f16 is still to do) |
+| 3D Channel | 8 | 8 | Cryptomatte's GPU path is slow (#473; the Selection is picked in the viewer with an eyedropper, or with the Selection tool while the effect is selected as in After Effects (#2839), quoted names with commas fixed); multi-layer EXR: one decode per frame for the picture and the channels, cache softly bounded at 1 GB (#474; holding channels as f16 is still to do) |
 | Audio | 13 | 0 | CPU by design (applied in the mixdown) |
 | Blur & Sharpen | 16 | 15 | Radial Blur keeps the layer edges as After Effects 2026 (713 now pixel-identical); Gaussian Blur interaction and output to be measured first ([fidelity/ae-2026-acceptance.md](fidelity/ae-2026-acceptance.md)) |
 | Channel | 13 | 13 | — |