Apply the masks to the thumbnail and the export, not only the screen

Reported as a thumbnail bug; the export had it too, which is the serious
half. You would have exported a photograph missing every local adjustment.

Both called the unmasked `render`, and the failure is silent by
construction: the generated shader always declares the mask binding and
always emits a block per active layer, so binding the empty placeholder
multiplies each of them by zero. No error, no warning, no missing texture —
the adjustments are simply not there. From inside either path there is
nothing to see.

Every path that produces pixels now goes through one helper that binds the
array, and that is the point of it being one helper rather than three
correct call sites. The array is rasterised in source space at proxy size
and sampled through the framing map, so one array serves every output size:
a 256px thumbnail and a 24 MP export bind the same texture.

Three tests, and the first is the fault stated directly — render the same
edit with and without the array and assert they *differ*. If binding it ever
stops mattering, the masks have stopped reaching the shader. The third
checks the masked share of the frame is the same at 32px and 128px, because
"both non-empty" would pass while a mask that scaled wrongly still ruined
every thumbnail.

core/dr-pipeline/src/lens.rs

@@ -54,7 +54,7 @@
 
 use std::fmt::Write as _;
 
-use crate::descriptor::{Attribute, OpDescriptor, ParamId};
+use crate::descriptor::{OpDescriptor, ParamId};
 use crate::operation::{Helper, Uniform};
 
 /// A coordinate-domain operation, applied before the source is sampled.
@@ -205,6 +205,7 @@ fn sanitise(id: &str) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::descriptor::Attribute;
     use crate::descriptor::{LocalizedKey, OpDescriptor, OpId, ParamDescriptor};
 
     static DESC_A: OpDescriptor = OpDescriptor {

core/dr-pipeline/src/operation.rs

@@ -24,7 +24,7 @@ use std::fmt::Write as _;
 
 use dr_types::{ColourSpace, Transfer};
 
-use crate::descriptor::{Attribute, OpDescriptor, ParamId, Presentation};
+use crate::descriptor::{OpDescriptor, ParamId, Presentation};
 use crate::framing::{Framing, FRAMING_UNIFORM_FIELDS};
 use crate::mask::MaskStack;
 
@@ -714,6 +714,7 @@ pub(crate) fn sanitise(id: &str) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::descriptor::Attribute;
     use crate::descriptor::{LocalizedKey, OpId, ParamDescriptor};
 
     static DESC_A: OpDescriptor = OpDescriptor {