Spec baseline exposure, Camera Raw tone and profile sync (D21)

camera-profiles.md §11-§14 close what 0.20.0 left open. Baseline
exposure is the file's plus the profile's offset, applied as a gain on
the camera matrix, and a copied profile carries the DNG's baseline so a
CR2 lands at the same brightness. The view transform gains a Camera Raw
curve — the profile's ProfileToneCurve, else the ACR3 default — applied
Camera Raw's way, on the outer channels in linear ProPhoto, and it is
the default for every raw (D21, the user's choice). Profiles sync
through .darkroom-derived/profiles on the server as a step of the
derived sync pass, not as a catalog table.

docs/dev/requirements.md

@@ -2437,6 +2437,7 @@ Rationale, evidence, and the eliminated alternatives are recorded in
 | D12 | Scope versus pace | **DECIDED 2026-09-19** — settled by events; full scope stands, no v1 date |
 | D18 | Derived images | **DECIDED 2026-09-19** — a merge writes a new source file; no multi-source Version |
 | D19 | Scene-referred pipeline | **DECIDED 2026-09-27** — edits on unbounded scene-linear colour; one view transform, last; per-body base curves retired |
+| D21 | Camera Raw tone for raws | **DECIDED 2026-10-03** — the view transform gains a Camera Raw curve (profile's, else ACR3 default, via RGBTone in ProPhoto), the default for every raw; Sigmoid stays a choice |
 | D20 | DCP camera profiles | **DECIDED 2026-10-02** — HueSatMap and LookTable as a scene operation after exposure; embedded profile first, then a matched `.dcp`; tone curve not applied; none shipped |
 
 ### D11 — product positioning
@@ -2772,6 +2773,28 @@ matrix does.
 *What it costs.* Every DNG with an embedded profile renders differently; previews refresh only when
 rendered again; tablet and desktop release together. The profiles directory does not sync yet.
 
+### D21 — Camera Raw tone for raws · **DECIDED 2026-10-03**
+
+**The view transform has two curves, and Camera Raw's is the default for every raw.** It is the
+profile's `ProfileToneCurve`, or the ACR3 default curve where the profile has none or there is no
+profile, applied Camera Raw's way — on the largest and smallest channel in linear ProPhoto, the
+middle placed proportionally — after `BaselineExposure`. D19's sigmoid stays as the other choice.
+Design: [camera-profiles.md](camera-profiles.md) §11–§13.
+
+*Why.* Measured on the library's 6D DNGs after D20 (camera-profiles.md §1): the profile tables
+lowered saturation, because Adobe's look tables were tuned to sit under this curve. The user's
+complaint was that Lightroom's rendering is more colourful, and this curve is most of the reason.
+Chosen by the user over limiting it to raws with a profile, or making it opt-in.
+
+*What it reverses in D19.* D19 rejected per-body curves as defaults because their provenance was
+unknown. A DCP's curve and the ACR3 table have known provenance — Adobe's, published — and so the
+objection that retired the base curves does not apply. D19's other half stands: nothing before
+the view transform clamps, and the curve is the view transform, last.
+
+*What it costs.* Every raw renders differently again, and highlights above display white clip
+where the sigmoid rolled them off; Sigmoid is one click away. Previews refresh only when rendered
+again; tablet and desktop release together.
+
 ### D16 — plugin licensing · **OPEN, post-v1**
 
 > Deferred with §3.10 on 2026-09-19. Still to be answered before the format is published as