LR-MASK-BRUSH: separate brush subtraction from erasing (#516)

docs/control-protocol.md

@@ -55,6 +55,12 @@ scrolling pans in both axes and respects the operating system's scrolling direct
 These gestures work in Detail (including editing tools and full-screen preview), Compare and Reference
 views, and only apply over their image areas. Panning stops at the image edges.
 
+Mask brushing uses the UI command `tool.brush` through `engine.execute`. With `{}` it activates
+painting on the current mask. `{"new": true}` creates a separate brush mask; `{"op": "add"}` or
+`{"op": "subtract"}` appends a brush component to the selected mask. Creating either starts in
+paint mode with the overlay visible. Brush Erase (or Alt while painting) removes strokes' coverage
+within that brush component; it is distinct from subtracting the component from the whole mask.
+
 ### When the library can't be saved
 
 With a persistent library, every command that changes something is written to the catalog journal (fsynced) before

docs/parity.md

@@ -31,7 +31,7 @@ and prints the summary; `cargo xtask parity --write` refreshes the summary table
 | H. Crop & rotate (CROP) | 9 | 0 | 0 | 1 | 6/6 (100%) | 3/3 (100%) |
 | I. Remove / healing (REM) | 7 | 1 | 2 | 2 | 4/4 (100%) | 2/3 (67%) |
 | J. Red eye (EYE) | 2 | 0 | 0 | 0 | — | 1/1 (100%) |
-| K. Masking (MASK) | 14 | 4 | 5 | 0 | 8/8 (100%) | 5/5 (100%) |
+| K. Masking (MASK) | 13 | 5 | 5 | 0 | 7/8 (88%) | 5/5 (100%) |
 | L. Presets (PRE) | 6 | 0 | 1 | 1 | 2/2 (100%) | 2/2 (100%) |
 | M. Versions & history (VER) | 5 | 0 | 0 | 0 | 1/1 (100%) | 3/3 (100%) |
 | N. Copy / paste / sync (SYNC) | 5 | 0 | 0 | 0 | 3/3 (100%) | 1/1 (100%) |
@@ -48,9 +48,9 @@ and prints the summary; `cargo xtask parity --write` refreshes the summary table
 | Y. Menus | 82 | 0 | 4 | 8 | 47/47 (100%) | 23/23 (100%) |
 | Z. Keyboard shortcuts (desktop) | 75 | 3 | 3 | 1 | 49/52 (94%) | 23/24 (96%) |
 | Lightroom Classic extras | 32 | 11 | 39 | 9 | — | 22/24 (92%) |
-| **Total** | 394 | 38 | 84 | 36 | 193/200 (97%) | 142/152 (93%) |
+| **Total** | 393 | 39 | 84 | 36 | 192/200 (96%) | 142/152 (93%) |
 
-Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **80.0%** of 516 in-scope rows — P0 98.2% of 200 · P1 95.7% of 152 · P2 42.9% of 163.
+Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **79.9%** of 516 in-scope rows — P0 98.0% of 200 · P1 95.7% of 152 · P2 42.9% of 163.
 <!-- /parity:summary -->
 
 ## Top gaps
@@ -352,13 +352,13 @@ under the UI command that wraps it (a no-op error); the UI command now wins.
 | LR-MASK-OBJECTS | Object selection | P2 | 🟡 | `cmd:mask.add` (`object`, `prompt`), `cmd:mask.objectPoint`, `cmd:mask.refineDetail`, `cmd:segment.prepare`, `cmd:segment.model.status`, `cmd:segment.model.download`, `cmd:segment.model.cancel`, `crates/segment`, `crates/engine/src/segment/mod.rs` | SAM 3 in pure Rust (candle; Metal on macOS, CPU elsewhere): Object tile → click to include, ⌥-click to leave out; Describe tile → a text prompt selects every instance ("sky", "the red car"); both also as Add/Subtract/Intersect components; + / − under the selected mask; comma lists (`car, road`); a zoomed-in detail pass for 5–10× finer edges on small objects; per-selection Edge (hard ↔ soft). The model runs on its own worker thread (the UI never waits; panics become errors), is unloaded after 10 min idle, and is optional: the segmentation is stored with the mask (288² logits), so renders and exports never need it. Weights are never bundled (SAM License): without them the app offers a consented background download (mirrors, resume, timeouts, SHA-256) — **but no default download location is configured yet** (users set `LIGHTCRAFT_SAM3_MIRRORS` or install by hand: the dialog names the three files, shows the model folder and links docs/ai-masks.md). Not verified against Lightroom's Select Object; no brush/box object mode; the first click on a photo waits for its analysis (~4 s on an M4 Pro, much longer on CPU) |
 | LR-MASK-PEOPLE | People parts | P2 | ⬜ | | shape exists (no UI): uses the photo's person / skin / hair / teeth / glasses mattes when it carries them (DNG semantic masks), else the subject heuristic |
 | LR-MASK-LANDSCAPE | Landscape classes | P2 | ⬜ | | shape exists, evaluates empty |
-| LR-MASK-BRUSH | Brush mask | P0 | ✅ | `cmd:tool.brush`, `cmd:mask.brushStroke` (`autoMask`), `crates/pipeline/src/masks.rs` | size/feather/flow/density/erase; Auto Mask: dabs weighted by similarity to the colour under the dab centre, refined by a guided filter on luminance (CPU + GPU); no A/B brushes, no pressure |
+| LR-MASK-BRUSH | Brush mask | P0 | 🟡 | `cmd:tool.brush`, `cmd:mask.brushStroke` (`autoMask`), `crates/pipeline/src/masks.rs` | size/feather/flow/density/erase; Create New Mask starts a separate brush in paint mode; live-preview gaps (#517) and stationary accumulation (#518) remain; Auto Mask: dabs weighted by similarity to the colour under the dab centre, refined by a guided filter on luminance (CPU + GPU); no A/B brushes, no pressure |
 | LR-MASK-LINEAR | Linear gradient | P0 | ✅ | `cmd:tool.linear`, `cmd:mask.update` | |
 | LR-MASK-RADIAL | Radial gradient | P0 | ✅ | `cmd:tool.radial`, `cmd:mask.update` | |
 | LR-MASK-COLORRANGE | Colour range | P1 | ✅ | `cmd:mask.add` (`colorRange`), `cmd:mask.sampleColor`, `cmd:mask.update`, `crates/pipeline/src/lib.rs` (`color_range_sample`) | Color tile → click the photo to sample (⇧-click adds, up to 5; samples taken in the space the mask compares in), Pick button, Refine slider |
 | LR-MASK-LUMRANGE | Luminance range | P1 | ✅ | `cmd:mask.add` (`luminanceRange`), `cmd:mask.update`, `crates/ui-egui/src/panels/masking.rs` (`range_controls`) | range bar with two handles (one undo step per drag), Smoothness, Show Luminance Map (B&W photo with the range tinted) |
 | LR-MASK-DEPTHRANGE | Depth range | P2 | ⬜ | | shape exists, needs depth data |
-| LR-MASK-COMBINE | Add / subtract / intersect | P0 | ✅ | `cmd:mask.addComponent` | |
+| LR-MASK-COMBINE | Add / subtract / intersect | P0 | ✅ | `cmd:mask.addComponent`, `cmd:tool.brush` | Add/Subtract > Brush creates a component with the chosen operation; Erase removes paint within that brush component |
 | LR-MASK-INVERT | Invert | P0 | ✅ | `cmd:mask.invert` | |
 | LR-MASK-AMOUNT | Mask amount | P1 | ✅ | `cmd:mask.adjust` (`amount`), `crates/ui-egui/src/panels/masking.rs` | |
 | LR-MASK-FEATHER-EDGE | Refine mask edges | P2 | ✅ | `cmd:mask.refine`, `crates/pipeline/src/masks.rs` (`evaluate_one`) | Refine Edges slider per mask: guided filter on the photo's luminance snaps soft mask edges to the photo's edges (rendered on the CPU) |