Merge branch 'worktree-agent-afd449f5e7a01e341' into integration

# Conflicts:
#	core/dr-gpu/src/adjust.rs
#	core/dr-pipeline/ops/README.md
#	core/dr-pipeline/src/lib.rs
#	docs/traceability.md

core/dr-pipeline/ops/README.md

@@ -250,6 +250,44 @@ count of source pixels (`RenderScale::source_pixels` — capture sharpening,
 luminance NR). `passes()` is given the scale and converts on the CPU. A radius
 in raw pixels is a different photograph on screen and in the exported file.
 
+## What is not a node, and why
+
+Three things act on every pixel and are deliberately not in this directory:
+the as-shot white balance, the camera matrix, and the **base curve**
+(FR-DEV-3e). They are emitted by [`../src/operation.rs`](../src/operation.rs)
+into the composed shader's fixed preamble, around the block of nodes.
+
+The test is not "does it transform a colour" — all three do. It is **whose
+decision is it**. A node is something a photographer chose: it has parameters,
+it moves off a neutral, it lands in the sidecar, it can be undone. These three
+are properties of the *file*, at the same standing as the masked-photosite crop
+(FR-RAW-3) and the stored orientation (FR-DEV-3h). Nobody chose the sensor's
+green sensitivity or the body's rendering; they are what reading the file
+correctly means.
+
+Making the base curve a node would have said the opposite in four places at
+once. It would have appeared in the develop panel as a control, so an
+unprofiled body would show a slider that does nothing. Its values would have
+gone into the sidecar, and sidecars are shared between devices and bodies
+(FR-NC-9) — one camera's rendering would follow an edit onto another camera's
+file. Its neutral would have had to be "the identity", so a profiled body would
+open reporting itself modified. And there is no seam through which a node could
+learn which camera took the frame: the profile arrives on the decoded image,
+travels through `DemosaicedImage` beside the matrix it belongs with, and is
+written into the uniform block by the same three lines in `dr-gpu` — which is
+exactly the path the matrix already took, because it is exactly the same kind
+of thing.
+
+What it *does* share with the tone curve node is the spline. The composer asks
+`ToneCurve` for its `curve_span`/`curve_eval` helpers rather than emitting a
+second copy, so a profile author placing a control point and a photographer
+dragging one mean the same thing by it.
+
+The order still reads correctly from this directory: the base curve runs after
+every node in the chain and before the conversion out of camera space. That is
+the same reasoning `exposure` records under `placement:` — corrections to
+capture are only meaningful on linear values, so the rendering goes last.
+
 ## Errors
 
 The build script reports failures by naming the key you got wrong, and exits