Merge PR #2981: Issue #2819: the histogram stays SDR when HDR is switched off

crates/ui-egui/src/panels/edit/histogram.rs: live_hdr_histogram added above main's histogram() (now in edit/histogram.rs, pub(crate))
docs/parity-checklist.md: main's Histogram row with this PR's HDR-off clause

docs/parity-checklist.md

@@ -139,7 +139,7 @@ differences and missing bindings are in [ui-parity.md](ui-parity.md#shortcuts).
 | LR-VIEW-SLIDESHOW | Slideshow | P2 | ✅ | `cmd:view.slideshow` | View ▸ Slideshow (⌥⌘↩): the photos in view full screen from the selected one, played with the library's playback settings (see LRC-SS-PLAYBACK: fades, random order, repeat, previews prepared ahead; `interval` / any setting overrides one run); Space pauses, ←/→ step (a cut), Esc ends; playback controls on pointer movement |
 | LR-VIEW-SECONDWINDOW | Second display window [Classic] | P2 | ✅ | `cmd:view.secondWindow`, `crates/ui-egui/src/panels/second.rs` | Window ▸ Second Window (⌘F11): the active photo fitted in its own native window with its own render (a floating panel where there are no native windows); loupe view only (no grid / compare / survey there) |
 | LR-VIEW-CLIPPING | Clipping indicators | P0 | ✅ | `cmd:view.clipping` | |
-| LR-VIEW-HISTOGRAM | Histogram | P0 | ✅ | `cmd:view.histogram`, `crates/ui-egui/src/panels/edit/histogram.rs`, `crates/ui-egui/src/panels/right.rs`, `crates/pipeline/src/lib.rs` (`hdr_histogram`) | stays at the top of the Edit panel while its sliders scroll under it (issue #2679, `the_histogram_stays_in_view_while_the_sliders_scroll`); HDR edits: SDR on the left half, the HDR range (0 to 5 stops above SDR white, a fixed scale) on the right with the headroom limit marked; colour bar (white, or Visualize HDR range's colours when that is on) and SDR / HDR labels; the plot's five tonal zones also drag to adjust their Basic control (LRC-DEV-HISTOGRAM-DRAG); it follows slider drags live (a small render beside the drafts, `Slot::HdrHistogram`) and never drops to the SDR layout mid-drag |
+| LR-VIEW-HISTOGRAM | Histogram | P0 | ✅ | `cmd:view.histogram`, `crates/ui-egui/src/panels/edit/histogram.rs`, `crates/ui-egui/src/panels/right.rs`, `crates/pipeline/src/lib.rs` (`hdr_histogram`) | stays at the top of the Edit panel while its sliders scroll under it (issue #2679, `the_histogram_stays_in_view_while_the_sliders_scroll`); HDR edits: SDR on the left half, the HDR range (0 to 5 stops above SDR white, a fixed scale) on the right with the headroom limit marked; colour bar (white, or Visualize HDR range's colours when that is on) and SDR / HDR labels; the plot's five tonal zones also drag to adjust their Basic control (LRC-DEV-HISTOGRAM-DRAG); it follows slider drags of an HDR edit live (a small render beside the drafts, `Slot::HdrHistogram`) and never drops to the SDR layout mid-drag; an edit with HDR switched off keeps its SDR histogram while it is dragged (#2819) |
 | LR-VIEW-HDR-DISPLAY | HDR display output | P2 | ⬜ | |, `apps/lightcraft/src/hdr_display.rs` (`choose`, `preferred_hdr_format`) | SDR/HDR decision (platform, surface format, OS headroom, `LIGHTCRAFT_HDR_DISPLAY=0`) is unit-tested and logged at start; always SDR today because eframe configures an 8-bit surface; no OS headroom query yet;  |
 
 ## D. Search & filter (FILT)
@@ -799,6 +799,7 @@ Latin stays upright. Advanced Japanese composition remains open. Regression cove
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-27 | patch | LR-VIEW-HISTOGRAM: an edit with HDR switched off no longer shows the last HDR drag's histogram while it is dragged (#2819); status unchanged |
 | 2026-10-25 | patch | LR-BEHAV-TITLEBAR: the top bar's title-bar gestures come from craft-window's `title_bar`: a double-click follows the system setting, and a press on a button, the search field or a panel floating over the bar never moves the window; status counts unchanged |
 | 2026-10-24 | minor | KEYC-METADATA, LRC-LIB-KEYWORDS: ⌥0 / ⌥⇧0 (`keyword.nextSet`, `keyword.previousSet`) go to the next / previous keyword set; status counts unchanged (KEYC-METADATA stays 🟡) |
 | 2026-10-24 | minor | KEYC-METADATA: ⌘K / Ctrl+K (`panel.addKeywords`, Add Keywords) shows the Keywords panel, opens Keywording and puts the cursor in the Add keyword box; status counts unchanged (KEYC-METADATA stays 🟡) |

docs/whats-new.md

@@ -1,5 +1,12 @@
 # What's new in LightCraft
 
+## 2026-10-30
+
+### The histogram stays SDR when HDR is switched off
+- After an HDR edit was dragged and HDR was then switched off, dragging a slider showed the old HDR histogram (with its
+  SDR / HDR colour bar) again until the drag ended. The histogram now follows the edit: an SDR edit shows the SDR
+  histogram while you drag, too.
+
 ## 2026-10-27
 
 ### The Edit menu groups Select Only Active Photo and Paste Settings from Previous with their kin