WIP: noise reduction

Checkpoint committed by the coordinator, not by the authoring agent: the
session hit its API limit mid-task and left this work uncommitted. Committed
so it survives, NOT because it is finished - expect failing tests and
half-applied changes. The agent resumes from here.

core/dr-pipeline/src/ops/mod.rs

@@ -26,6 +26,12 @@
 //! parameters at all. A schema stretched to cover those would be a worse
 //! language than Rust, aimed at one caller each.
 //!
+//! [`noise_reduction`] is an exception for a different reason again: it is a
+//! *kernel*, and a declared node's `wgsl:` is handed a colour with no way back
+//! to a coordinate. It runs in [`crate::detail`] instead, deciding at each
+//! render how many dispatches to emit and converting a radius stated in sensor
+//! pixels into the render pixels this frame is being drawn at.
+//!
 //! Both publish the same [`crate::descriptor::OpDescriptor`], so nothing
 //! downstream can tell them apart. A hand-written node still declares its
 //! place in the chain in `ops/<id>.yaml` with `rust:`, so the directory
@@ -44,12 +50,14 @@ pub mod aberration;
 pub mod colour_mixer;
 pub mod curve;
 pub mod distortion;
+pub mod noise_reduction;
 pub mod vignetting;
 
 pub use aberration::Aberration;
 pub use colour_mixer::ColourMixer;
 pub use curve::ToneCurve;
 pub use distortion::Distortion;
+pub use noise_reduction::NoiseReduction;
 pub use vignetting::Vignetting;
 
 // The declared nodes, plus `helpers` and `chain`. Generated into OUT_DIR by