LR-BEHAV-SIDEBAR-STICKY: a long section's header stays in sight; sections are easier to tell apart

Pinned header at the top of the sidebar, hairlines between sections, the fold
chevron in the rows' triangle column, a count on folded sections, fainter zero
counts. From review: a move nobody could see is no move, ui.set refuses
`sidebar` together with `collapsedSidebar` and unknown names in the latter.
Translations and What's New for the sidebar work.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/parity.md

@@ -44,13 +44,13 @@ and prints the summary; `cargo xtask parity --write` refreshes the summary table
 | U. Map & location (MAP) | 0 | 1 | 1 | 0 | — | 0/1 (0%) |
 | V. Preferences (PREF) | 6 | 2 | 2 | 2 | 1/1 (100%) | 4/5 (80%) |
 | W. Cloud & AI infrastructure (CLOUD / AI) | 1 | 0 | 1 | 2 | — | — |
-| X. Cross-cutting behaviours (BEHAV) | 21 | 6 | 1 | 1 | 8/8 (100%) | 6/9 (67%) |
+| X. Cross-cutting behaviours (BEHAV) | 22 | 6 | 1 | 1 | 8/8 (100%) | 6/9 (67%) |
 | Y. Menus | 83 | 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 | 33 | 15 | 35 | 9 | — | 23/25 (92%) |
-| **Total** | 401 | 49 | 73 | 36 | 192/200 (96%) | 143/155 (92%) |
+| **Total** | 402 | 49 | 73 | 36 | 192/200 (96%) | 143/155 (92%) |
 
-Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **81.4%** of 523 in-scope rows — P0 98.0% of 200 · P1 95.2% of 155 · P2 48.5% of 167.
+Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **81.4%** of 524 in-scope rows — P0 98.0% of 200 · P1 95.2% of 155 · P2 48.8% of 168.
 <!-- /parity:summary -->
 
 ## Top gaps
@@ -529,6 +529,7 @@ under the UI command that wraps it (a no-op error); the UI command now wins.
 | LR-BEHAV-SIDEBAR-SECTIONS | Left-sidebar sections share one frame and one arrangement | P2 | ✅ | `crates/ui-egui/src/sidebar.rs` (`SidebarSection`, `SidebarLayout`), `crates/ui-egui/src/panels/left.rs` (`section`, `section_header`, `tree_toggle`), `crates/ui-egui/src/tests_panels.rs` | Albums, Local, By Date, Folders and Keywords are drawn by one `section` frame (the same gap above, header, fold and accessibility name) from one arrangement, `sidebar` in the UI state: a list of `{id, hidden, collapsed}` top to bottom, also settable with `ui.set`. Whatever is read, every section is in it exactly once (unknown and repeated entries are dropped, the rest follow in the usual order), so a damaged or newer settings file never loses the other settings. Rows that open (album folders, Local folders, dates, library folders, keywords) share `tree_toggle`: the same triangle, the same remembered open state, announced as Expand / Collapse. A section with nothing to list (Folders before anything is imported, Keywords before any is added) stays, open, with a one-line note in place of rows (`sidebarEmpty:<id>`) instead of disappearing. `ui.set` reads `sidebar` strictly (`SidebarLayout::parse`): an unknown or repeated section, or a flag that is not true / false, is refused and changes nothing; sections left out follow in the usual order, shown and open; the older `collapsedSidebar` list still folds and unfolds. My Photos (All Photos, Recently Added, Picks, Missing Photos, Recently Deleted) is not a section: it stays on top |
 | LR-BEHAV-SIDEBAR-HIDE | Show and hide left-sidebar sections | P2 | ✅ | `cmd:view.sidebarSection`, `cmd:view.sidebarReset`, `crates/ui-egui/src/sidebar.rs`, `crates/ui-egui/src/panels/left.rs` (`sections_menu`), `crates/ui-egui/src/menubar.rs`, `crates/ui-egui/src/tests_panels.rs` | View ▸ Sidebar Sections lists Albums, Local, By Date, Folders and Keywords in the sidebar's order, each checked while shown; unchecking one takes its header and rows off the sidebar, checking it puts it back where and how it was (still folded if it was). The same list opens with a right-click on any section header (with Hide This Section first; widgets `sidebarMenu:hide`, `sidebarMenu:section:<id>`, `sidebarMenu:reset`) and on the My Photos title (`sidebarTitle`), which is always there, so hidden sections can always come back. Reset Sidebar Sections (enabled once something changed) shows and opens every section in the usual order. `view.sidebarSection` `{section, show?, collapsed?}` flips shown / hidden when neither flag is given and refuses an unknown section or a flag that is not true / false. Hiding the section of what the grid shows (an album, a keyword filter) leaves the grid as it is; an album made while Albums is hidden or folded brings Albums back, open. Kept with the UI state (`sidebar`). My Photos itself can't be hidden |
 | LR-BEHAV-SIDEBAR-REORDER | Reorder left-sidebar sections | P2 | ✅ | `cmd:view.sidebarMoveSection`, `crates/ui-egui/src/sidebar.rs` (`move_before`, `move_by`), `crates/ui-egui/src/panels/left.rs` (`section_drag`, `section_drop_before`, `section_drag_feedback`), `crates/ui-egui/src/tests_panels.rs` | drag a section by its header: its name follows the pointer, a line (`sidebarSectionDrop`) shows the gap it would go to (above the section whose upper half the pointer is over, or below the last), releasing over the sidebar moves it there, Esc or releasing elsewhere leaves it; the sidebar scrolls when the drag nears its top or bottom edge. A click on the header still folds the section, and an album dragged onto the Albums header is still an album drag. The header's menu has Move Up / Move Down (`sidebarMenu:moveUp` / `moveDown`), one shown section at a time, stepping over hidden ones, disabled at the ends. `view.sidebarMoveSection` `{section, direction: up\|down}` or `{section, before: <section>\|null}` (null: last) answers `{moved, order}`. The order is kept with the UI state (`sidebar`). Recently Deleted is listed with My Photos (below Picks / Missing Photos), not after the sections. Not here: dragging My Photos, or rows from one section into another |
+| LR-BEHAV-SIDEBAR-STICKY | Pinned section header and section look | P2 | ✅ | `crates/ui-egui/src/panels/left.rs` (`pinned_header`, `section_header`, `empty_hint`), `crates/ui-egui/src/tests_panels.rs` | while the rows of an open section are in view but its header has scrolled away, a copy of the header (`sidebarSectionPinned:<id>`, with the section's buttons and menu) stays at the top of the sidebar; the next section's header pushes it out; folding from it brings the section's own header into view. Sections are told apart by a hairline in the gap above each; the fold chevron sits in the gutter, in the column of the rows' triangles (`sidebarSectionChevron:<id>`); a header highlights under the pointer; a folded section shows how many top-level rows it holds (`sidebarSectionCount:<id>`, with Show Photo Counts); a count of 0 is fainter. Not here: a height of its own per section (one scroll area serves the whole sidebar), a count for Recently Added, Local's Browse Folder… as a header button |
 | LR-BEHAV-PANEL-RESIZE | Resizable side panels | P1 | ✅ | `crates/ui-egui/src/panels/mod.rs` (`resizable_side`), `crates/ui-egui/src/state.rs` (`LEFT_WIDTH`, `RIGHT_WIDTH`), `crates/ui-egui/src/tests_panels.rs` | drag the left sidebar's right edge (200–480 pt) or the right panel's left edge (250–520 pt); the photo area keeps ≥ 360 pt; widths are kept across panels, views and restarts (`leftWidth` / `rightWidth` in the UI state); the Presets column stays fixed |
 | LR-BEHAV-EMPTY-STATES | Empty states | P1 | ✅ | `crates/ui-egui/src/panels/mod.rs` (`empty_message`) | |
 | LR-BEHAV-TOOLTIPS | Tooltips with shortcuts | P0 | ✅ | `crates/ui-egui/src/panels/bottombar.rs` | |

docs/whats-new.md

@@ -2,6 +2,19 @@
 
 ## October 2026
 
+### Sidebar sections
+- Arrange the left sidebar your way: drag Albums, Local, By Date, Folders or Keywords by its header to move it (a line
+  shows where it will go), or right-click a header for Move Up / Move Down.
+- Hide the sections you don't use: View ▸ Sidebar Sections, or right-click a header ▸ Hide This Section. Right-click
+  the My Photos title to bring one back, or choose Reset Sidebar Sections. The arrangement is remembered.
+- In a long section, the header stays at the top of the sidebar while you scroll through its rows, so you always see
+  which section you are in and can fold it from there.
+- Sections are easier to tell apart: a hairline between them, the fold chevron in the same column as the rows'
+  triangles, a highlight under the pointer. A folded section shows how many rows it holds, counts of 0 are fainter,
+  and a section with nothing in it says so instead of disappearing.
+- Recently Deleted is listed with All Photos, Recently Added and Picks under My Photos.
+- Agents: `view.sidebarSection`, `view.sidebarMoveSection`, `view.sidebarReset`; `ui.set` takes `sidebar`.
+
 ### Activity stack
 - Long-running tasks show in one place, top left under the top bar, as in Lightroom Classic (issue #345): imports and
   folder scans, exports (and the contact sheet PDF), Synchronize Folder, Build / Smart Previews, Lightroom catalog import, Photo Merge, model downloads, the face scan,