Combine files: a thumbnail grid, card sizes and card actions (refs #611) (#777)

Combine files shows each file as a card (the default; Grid/List kept in
the settings, --combine-view): the first page it adds, stacked when it
adds more, its name shortened in the middle. Cards select (click, Ctrl,
Shift, arrows by card and by row), drag to reorder (one undo step; the
grid scrolls at its edges) and share the list's toolbar, selection and
history. Locked, unreadable, bad-range and unmeasurable files say why.

Thumbnails render off the UI thread, only for cards in view: at most
three render threads at once, counted until they exit (no watchdog
replacements), a 32 MB texture budget, keys that never show another
page, password or file, and one heavy step per frame on the web.

Cards are sized from 60% to 200% (toolbar slider and buttons, Ctrl
+/-/0, Ctrl+wheel or pinch over the grid, kept in the settings,
--combine-zoom), keeping the card under the pointer in place. Hovering
a card shows its actions over the top of its page: remove that file,
and a magnifier that shows it large, flipping through the pages it
adds; the same on a right click, and Space by keyboard. The toolbar
wraps between groups at narrow widths.

RenderPool gains retire(), without_replacements() and threads() so a
caller can bound the render threads that exist at once.

Co-authored-by: Andrew Taylor <andrew.taylor@tayeng.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

parity/acrobat-features.toml

@@ -2951,7 +2951,19 @@ status = "shipped"
 commands = ["page.combine"]
 tools = ["doc_combine"]
 evidence = ["crates/ui-egui/tests/editing.rs::column_headings_sort_the_list_and_flip_on_the_second_click", "crates/ui-egui/tests/editing.rs::ctrl_and_shift_clicks_select_several_files_that_move_and_go_together", "crates/ui-egui/tests/editing.rs::undo_and_redo_restore_the_combine_list", "crates/automation/tests/automation.rs::combine_extract_and_split"]
-notes = "Sort by any column (name in natural order, pages, size, modified, warnings), ascending or descending; multi-select (Ctrl/Shift) and move up/down, Alt+arrows or drag; every change undoable. doc_combine combines in the order its paths are given."
+notes = "Sort by any column (name in natural order, pages, size, modified, warnings), ascending or descending; multi-select (Ctrl/Shift) and move up/down, Alt+arrows or drag (rows in the list, cards in the grid); every change undoable. doc_combine combines in the order its paths are given."
+
+[[feature]]
+id = "organize.combine-thumbnails"
+title = "Thumbnail (grid) view of the files before combining"
+area = "D"
+tier = "P2"
+milestone = "M4"
+status = "shipped"
+commands = ["page.combine"]
+tools = ["doc_combine"]
+evidence = ["crates/ui-egui/tests/combine_grid.rs::combine_shows_a_grid_by_default_and_the_view_is_kept_in_the_settings", "crates/ui-egui/tests/combine_grid.rs::cards_select_like_the_list_and_the_selection_survives_switching_views", "crates/ui-egui/tests/combine_grid.rs::dragging_a_card_moves_it_and_undo_puts_it_back", "crates/ui-egui/tests/combine_grid.rs::a_dragged_selection_moves_together_to_the_first_and_last_gaps", "crates/ui-egui/tests/combine_grid.rs::thumbnails_show_the_first_page_each_file_takes", "crates/ui-egui/tests/combine_grid.rs::many_files_render_only_what_is_in_view_a_few_at_a_time", "crates/ui-egui/tests/combine_grid.rs::long_thin_pages_get_thumbnails_within_the_size_limits", "crates/ui-egui/tests/combine_grid.rs::combine_follows_the_order_shown_in_the_grid", "crates/ui-egui/src/combine_grid.rs::render_threads_never_exceed_three_while_files_come_and_go", "crates/ui-egui/src/combine_grid.rs::textures_over_budget_go_longest_unseen_first_and_those_in_view_stay", "crates/ui-egui/src/combine_grid.rs::on_the_web_one_thumbnail_waits_at_a_time", "crates/ui-egui/tests/combine_grid.rs::a_file_whose_pages_cant_be_measured_says_there_is_no_preview", "crates/ui-egui/tests/combine_grid.rs::the_toolbar_sizes_the_cards_within_limits_and_the_size_is_kept_in_the_settings", "crates/ui-egui/tests/combine_grid.rs::ctrl_keys_and_ctrl_wheel_size_the_cards_and_leave_the_window_alone", "crates/ui-egui/tests/combine_grid.rs::zooming_keeps_the_card_under_the_pointer_in_place_and_thumbnails_never_go_blank", "crates/ui-egui/tests/combine_grid.rs::zooming_quickly_never_runs_more_than_three_render_threads", "crates/ui-egui/tests/combine_grid.rs::hovering_a_card_shows_its_trash_and_magnifier_and_only_then", "crates/ui-egui/tests/combine_grid.rs::the_card_trash_removes_only_that_file_and_undo_brings_it_back", "crates/ui-egui/tests/combine_grid.rs::the_magnifier_shows_the_file_large_and_flips_through_the_pages_it_adds", "crates/ui-egui/tests/combine_grid.rs::the_preview_closes_when_its_file_leaves_and_keeps_to_three_render_threads", "crates/ui-egui/tests/combine_grid.rs::a_right_click_on_a_card_offers_preview_and_remove", "crates/ui-egui/tests/combine_grid.rs::space_shows_the_selected_file_large_in_the_grid_and_the_list"]
+notes = "Combine files shows a card per file (the default; Grid/List toggle kept in the settings, --combine-view grid|list): the first page the file contributes (its page range's first page), stacked when it contributes more, and its name shortened in the middle. Cards are sized from 60% to 200% (toolbar slider, buttons and percentage reset, Ctrl/⌘ +/−/0, Ctrl/⌘ with the wheel or a pinch over the grid; kept in the settings, --combine-zoom 60..200), keeping the card under the pointer in place. Hovering a card shows its own actions along the top of its page: remove that file only (whatever else is selected; undoable) and a magnifier that shows the file large, flipping through the pages it adds (buttons, Left/Right; Esc, close or a click outside closes it), also on the card's right-click menu, and Space shows the selected file large (the way there by keyboard). Cards select (click, Ctrl, Shift, arrows by card and by row), drag to reorder (one undo step; the grid scrolls at its edges) and share the list's toolbar. Thumbnails render off the UI thread, only for cards in view, sized to both sides of the page and at most 768 px; at most three render threads at once, counted as threads until they exit (no watchdog replacements; a page stuck for good in one step that can't be interrupted keeps its thread, and so its place, for the rest of the run); textures out of view are dropped over a 32 MB budget (those in view are kept). Locked, unreadable and bad-range files show why instead of a page, and a file whose page size can't be read (e.g. opened with an RC4 owner password) says No preview; page ranges are edited in the list. On the web a thumbnail, and the page shown large, render on the UI thread (one per frame, and only one waits at a time), so a very slow or very large page stalls that frame. Missing: expanding a file into its pages, and moving or removing single pages before combining (#611)."
 
 [[feature]]
 id = "organize.combine-options"