Effects: EXtractoR picks layers and channels of multi-layer EXRs (#295)

EXtractoR's Red, Green, Blue and Alpha are text parameters naming
channels, and Effect Controls drew nothing for text parameters: there
was no way to choose a layer or channel. And a multi-layer OpenEXR file
whose colour is only in named layers (`diffuse.R`, Blender's
`ViewLayer.Combined.R`) didn't import at all: the image decoder wants an
unnamed RGB layer ("does not contain non-deep rgb channels").

- Effect Controls: EXtractoR gets a Layer popup listing the footage's
  OpenEXR layers. Picking one sets red, green, blue and alpha to its
  channels in one undo step, as After Effects' EXtractoR dialog does (a
  one-channel layer such as depth goes in all three colours). Red /
  Green / Blue / Alpha are popups of the layer's own R, G, B, A, every
  channel of the file, and (none). The lists are read only while open,
  so playing an EXR sequence doesn't parse files on the UI thread.
- `layer.channels {layer}` lists a layer's EXR layers and channels and
  what each layer shows in red, green, blue and alpha, for agents.
- Media: an EXR without an unnamed RGB layer imports and shows its
  colour layer (one named combined, beauty or rgba first); its channels
  stay available to EXtractoR and the 3D Channel effects.
- Raster: AuxChannels::layers / layer_rgba and split_channel.

Test: extractor_shows_the_chosen_layer_and_channels_of_a_layered_exr
(host: a layered EXR written with the exr crate imports, layer.channels,
EXtractoR renders spec and depth; it failed to import before),
extractor_offers_the_exr_layers_and_channels (UI: Layer popup, one undo
step, channel popup), layered_exr_without_an_unnamed_rgb_layer_imports
(media).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/agents.md

@@ -207,6 +207,10 @@ build real projects through these interfaces; they are worked examples of everyt
   `{"colors":[[0,"#0080ff"],[1,[1,1,0]]],"opacities":[[0,1],[1,0.5]]}`.
 * **Image sequences** import at 30 fps (Settings ▸ Import); `file.interpretFootage {"items":[id],
   "frameRate":12}` conforms them (the item and layers that ran to its end get the new length).
+* **Multi-layer OpenEXR**: `layer.channels {layer}` lists a footage layer's EXR layers and
+  channels (`{"layers":[{"name":"diffuse","rgba":["diffuse.R","diffuse.G","diffuse.B",""]}]}`);
+  EXtractoR shows them when its `red` / `green` / `blue` / `alpha` are set to those names
+  (`prop.set {"path":"effects/#1/red","value":"depth.Z"}`). Effect Controls offers them as popups.
 * **Masks**: `layer.addMask {layer, shape: rect|ellipse, rect}` first, then `layer.mask.set
   {field: feather|expansion|opacity, value}`.
 * **Renders**: `renderQueue.add {comp, format: h264|prores|webm|png…, channels: rgba,

docs/parity.md

@@ -190,7 +190,7 @@ Mocha and Cineware are third-party and not counted.
 
 | Category | Effects | Notes |
 |---|---|---|
-| 3D Channel | 3D Channel Extract, Cryptomatte, Depth Matte, Depth of Field, EXtractoR, Fog 3D, ID Matte, IDentifier | Read auxiliary channels: multi-layer OpenEXR (any `layer.channel`, Cryptomatte manifests from the header) or the compositor's own depth / layer-ID / normal / UV / Cryptomatte pass for precomps of 3D comps. |
+| 3D Channel | 3D Channel Extract, Cryptomatte, Depth Matte, Depth of Field, EXtractoR, Fog 3D, ID Matte, IDentifier | Read auxiliary channels: multi-layer OpenEXR (any `layer.channel`, Cryptomatte manifests from the header; EXtractoR picks a layer and channels from popups of the footage's layers and channels, `layer.channels`, #295) or the compositor's own depth / layer-ID / normal / UV / Cryptomatte pass for precomps of 3D comps. |
 | Immersive Video | VR Blur, VR Chromatic Aberrations, VR Color Gradients, VR Converter, VR De-Noise, VR Digital Glitch, VR Fractal Noise, VR Glow, VR Plane to Sphere, VR Rotate Sphere, VR Sharpen, VR Sphere to Plane | Seam-aware equirectangular processing (wrap-around, pole continuation, latitude-scaled filters), mono / over-under / side-by-side layouts; VR Converter between equirectangular, cube maps (4:3, 3:2, 6:1), sphere map and 2D. |
 | Color Correction | OCIO CDL / Color Space / Display / File / Look Transform, Color Stabilizer | Built-in minimal OCIO-style config (ACES2065-1, ACEScg, ACEScct, sRGB, Rec.709, Rec.2020, Display P3, linear variants, XYZ) from published matrices and transfer functions; `.cube` / `.3dl` / `.csp` LUTs and ASC `.cc` / `.ccc` / `.cdl`. Custom `.ocio` config files are read (Configuration ▸ Custom: colorspaces, roles, displays/views; Matrix, File, Exponent, Log, LogAffine, CDL, Range and Group transforms). |
 | Distort | CC Flo Motion, Liquify, Rolling Shutter Repair | Liquify strokes are effect data replayed into a displacement mesh (`liquify.stroke` / `liquify.clear` commands; no interactive viewer brush yet). Rolling Shutter Repair uses the KLT tracker. |