komorebi/docs/dev/core-model.md

The core model: KDE and Windows compared, and the split into komorebi-core

Status: measurement and proposal (plan step 9 preparation, KDE side). Measured at the tip of wip-u-kfde (based on wip-main 633e7453); the Windows tree is komorebi/src, KDE is komorebi-for-kde/komorebi/src, macOS (komorebi-for-mac/komorebi/src) is listed only where it helps. Nothing here has been run on Windows or macOS.

1. Measured differences

"Code lines" drop // lines and blank lines and strip indentation, so KDE's much heavier doc comments do not count; the inline #[cfg(test)] modules are included. "Changed" is the number of </> lines of diff between the two stripped files (an insertion of n lines counts n, a replacement of n lines counts 2n). "Identical" is the number of stripped lines present in both in the same order (a common subsequence, so it is a lower bound on shared text).

file	code lines Windows / KDE / macOS	changed W vs K	changed K vs M	changed W vs M	identical W&K
container.rs	230 / 254 / 241	196	119	185	144
monitor.rs	643 / 666 / 675	613	205	616	348
workspace.rs	2203 / 2491 / 2196	2314	1097	2113	1190
window.rs	1134 / 916 / 1641	1168	1413	1767	441
window_manager.rs	4716 / 4023 / 4896	4543	1597	5434	2098

Whole-file raw diff sizes (comments included): container 271, monitor 752, workspace 3167, window 1520, window_manager 6358 changed lines (Windows vs KDE). ring.rs is already shared (crates/komorebi-collections, Ring, Lockable).

Two things stand out. First, every file KDE and macOS share is much closer to each other than either is to Windows (K vs M changed is a third to a half of W vs K for monitor, workspace, window_manager, static_config, state). Windows is the odd one out, mostly because it carries older and larger machinery (see section 2). Second, the structs themselves are almost the same: Workspace has 31 fields on both sides and they differ only in the order of work_area_offset_rules/work_area_offset; the differences are in the methods around them.

2. Platform-specific fields and methods, per layer

container (smallest)

• Same fields (id, locked, windows: Ring<Window>). Windows' windows is private and locked has #[serde(default)]; KDE's windows is pub.
• Window id type: hwnd: isize (Windows) vs id: u32 (KDE) in contains_window, idx_for_window, hide(omit).
• Windows only: hwnd_from_exe (KDE keeps only idx_from_exe), Window::restore_with_border / hide_with_border in load_focused_window (Windows' border and stackbar are separate windows). exe() returns Result on Windows, Option on KDE.
• After the converge revisions of this stack the signatures are the same (add_window(Window), hide(&self, Option<id>), restore(&self), load_focused_window(&mut self), no Result) and the item order is the same. What is left is the id type and the three Windows-only lines above.

monitor

• Windows only fields: name, device_id, workspace_names: HashMap<usize, String>; serial_number_id is Option<String> (KDE: String); id is isize (KDE u32).
• Windows only methods: none in the public API; KDE has assign_windows_to_workspaces (it pushes the workspace of each window to the compositor's desktops, Backend::set_window_workspace).
• Behaviour that differs: Windows load_focused_workspace restores/hides workspaces itself, KDE asks the compositor to switch desktops (Backend::switch_workspace) and tiles what is in front; the Windows update_workspaces_globals pushes padding/border/work area into every workspace (WorkspaceGlobals), KDE calls update_workspace_globals(idx, offset) for the focused one. KDE has a MonitorInformation with 4 fields, Windows 6.
• BORDER_ENABLED (Windows) vs BORDER_DRAWN (KDE): the compositor draws borders.

workspace

• Windows only methods: windows_on_show, border_kinds_on_show, hwnd_from_exe.
• KDE only methods: adopt_maximized_window, focus_floating_window, focus_previous_floating_window, prune_duplicate_windows, reap_invalid_windows, remove_floating_window (my reading, not verified: KDE learns of closes and moves through the bridge snapshot, so the workspace reaps and prunes).
• 42 of 45/48 pub fn names are common. Windows restore/hide take the monitor handle and wallpaper and do the showing and hiding (WindowsApi, 8 mentions in the file); KDE leaves showing to the compositor (5 backend() calls).
• Scrolling layout glue (scrolling.rs): 1328 lines KDE, 1315 macOS, ~2200 Windows; measured first, not part of this comparison.

window (not shared: the platform handle)

• Window { hwnd: isize } (Windows, methods that call WindowsApi, 1134 code lines) vs Window { id: u32 } (KDE, Copy, every method calls backend(), 916 code lines) vs macOS (AX element, application, observer; not Copy, 1641 code lines).
• Both Windows and KDE Window are Copy handles, which is what lets the container and workspace code hold windows by value. macOS is not (clone).
• Window is where the split goes: the core must not call a method of Window that does not exist on all three.

window_manager

• Windows only fields: known_hwnds, virtual_desktop_id, uncloack_to_ignore, has_pending_raise_op, pending_move_op with a handle and rect, already_moved_window_handles of isize.
• KDE only fields: opacity_applied, minimized_windows, pending_resize_op, live_resize, known_window_ids (a u32 map); pending_move_op has no rect.
• 43 WindowsApi mentions in Windows' window_manager.rs, 15 backend() in KDE's. Every one of them becomes a Backend call or a Window method in the core.
• process_command and process_event are not in this table (see section 4 and the plan).

3. Proposed split: komorebi-core

komorebi-core                 (new crate, no platform dependency)
  ring, container, monitor, workspace, window_manager      (generic)
  trait Platform: Backend + { type Window; hooks }         (what is not in Backend)
komorebi-backend              (exists: Backend, WindowId, MonitorId, WindowInfo, Error, Capability)
komorebi (windows) / (kde) / (mac)
  Window (the platform handle), the Backend implementation, event sources, borders, ...

Generic over what:

• WindowManager<P: Platform>, with Platform::Window: Copy + Eq + Hash + Serialize + Deserialize and fn id(&self) -> WindowId. The three id types (isize, u32, u32) disappear into WindowId (WindowId::from_hwnd/from_u32, already in komorebi-backend). macOS needs Clone instead of Copy: the generic code has to take &P::Window and clone, or macOS keeps a Copy handle and an id registry as the seam doc proposes (docs/dev/seam.md section 7, consequence 1).
• Backend is a trait object or a type parameter; docs/dev/seam.md and the KDE conversion show it can be the shared trait unchanged, plus KDE's extension (drag_*, look, wallpaper) behind Platform hooks.
• Methods that are still platform behaviour (Window::hide_with_border, showing and hiding a workspace on Windows vs asking for a desktop on KDE) move behind two hooks: Platform::show_workspace(monitor, idx) and Platform::hide_workspace(...), with the Windows implementation hiding/restoring windows and the KDE one calling Backend::switch_workspace.

Exact order of layers (bottom-up, as in the plan)

1. ring is done (komorebi-collections).
2. container (230 lines): needs Window generic and id(). Smallest; do first. Windows must rename hwnd parameters to WindowId or an id() accessor and give exe() the KDE return type (Option<String>) or both use Result.
3. monitor (643): needs Workspace generic, MonitorId, and the Platform show/hide hooks. Windows' extra fields (name, device_id, workspace_names) stay in the shared struct as Option/default fields or become a P::MonitorExtra associated type; KDE serial_number_id becomes Option<String> with "" mapped to None.
4. workspace (2203): by far the biggest; the platform split is restore/hide/windows_on_show/ border_kinds_on_show (Windows) and reap/prune/adopt_maximized (KDE). Scrolling glue is measured before it moves.
5. window_manager (4716): after the first three are shared. The platform fields (section 2) go in a P::State associated type.
6. the flat router and process_event (separate steps in the plan).

4. What KDE has done (this stack) and what Windows must do before the crate exists

Landed on wip-u-kfde (all native tests green, none of it run on a VM):

• KDE's Backend extends the shared trait; ids, errors and info types are the shared ones at the trait; the core still holds Window { id: u32 } and converts at the call.
• container.rs and monitor.rs are in the same order as Windows', and Container has the Windows signatures (add_window(Window), infallible hide, restore, load_focused_window).
• All process_command arms longer than 20 lines are named methods (list in section 5).

I did not create the shared crate: the Windows tree still has isize handles in Container, Monitor::id: isize, and calls WindowsApi directly in 43 places of window_manager.rs. Windows (kfw) has to:

1. Finish adopting Backend in window_manager.rs, workspace.rs, monitor.rs (the 8 + 43 + 2 WindowsApi call sites there), so no core file names WindowsApi.
2. Give Container the same API KDE now has: accept a WindowId (or Window::id()), return Option from exe(), and drop hwnd_from_exe or move it to a platform extension.
3. Make Monitor.id and serial_number_id the shared types (MonitorId, Option<String>), which changes what komorebic state prints for Windows (a BEHAVIOUR change for the JSON; a test must pin it).
4. Convert its own multi-line process_command arms (the plan counts 22-23 per platform) into named methods with the same names KDE used (section 5), so the router can later be shared.

5. process_command: arms over 20 lines (KDE, before conversion)

arm	lines	now
ToggleWorkspaceLayer	90	toggle_workspace_layer()
EagerFocus	75	eager_focus(exe)
ResizeWindowAxis	60	resize_window_axis(axis, sizing)
IgnoreRule	55	add_ignore_rule(identifier, id)
Query	51	answer_query(query, reply)
SessionFloatRule	39	add_session_float_rule()
ReplaceConfiguration	34	replace_configuration(config)
CycleFocusEmptyWorkspace	32	cycle_focus_empty_workspace(direction)
CloseWorkspace	29	close_workspace()
MoveContainerToLastWorkspace	28	move_container_to_last_workspace(follow)
SendContainerToLastWorkspace	27	same method, follow = false
CycleFocusWorkspace	26	cycle_focus_workspace(direction)
LayoutRatios	23	set_layout_ratios(columns, rows)
BorderColour	21	set_border_colour(kind, r, g, b)
NamedWorkspaceRule	21	add_named_workspace_rule(identifier, id, workspace)
InitialNamedWorkspaceRule	21	add_initial_named_workspace_rule(identifier, id, workspace)
ToggleWorkspaceWindowContainerBehaviour	21	toggle_workspace_window_container_behaviour()

All are pub fn name(&mut self, ...) -> eyre::Result<()> in impl WindowManager (process_command.rs), except set_border_colour, which cannot fail.

6. First layer moved: Container is in komorebi-core (wip-u-core)

Done, on a throwaway merge of wip-u-kfde and wip-u-kfw (bookmark wip-u-core):

• crates/komorebi-core (root workspace member; KDE takes it by path) holds Container<W>, moved from the KDE file and made generic, and the trait ContainerWindow that says what a container asks of a platform window: type Id (isize on Windows, u32 on KDE), id, exe_name, hide_window, restore_window, and the pair hide_stacked / restore_stacked that load_focused_window uses (on Windows they leave the border alone, on KDE they are the plain ones). The container makes no Backend call itself.
• KDE and Windows each have type Container = komorebi_core::Container<Window> plus the ContainerWindow impl for their Window. Windows keeps hwnd_from_exe as the extension trait ContainerExt (workspace.rs imports it). The macOS tree does not use the crate yet and still type-checks.
• The JSON of a container is pinned by a test in each tree and in the crate (id, locked, windows: {elements, focused}); locked may be missing when read (KDE gained that from Windows); the schemars schema of Container<W> is renamed to Container, with a test.
• The Windows converge is marked BEHAVIOUR because it was only type-checked (clippy) and the crate's tests run natively; the Windows e2e scenarios it needs are in that revision's body.

Where it stops: Monitor

After kfw's convergence the Windows and KDE monitor.rs still differ by 657 changed code lines (710 vs 675 lines), and the difference is not mechanical:

• Fields: Windows has name, device_id, workspace_names: HashMap<usize, String>; serial_number_id is Option<String> (KDE String); id is a MonitorId that the Windows file serialises through hmonitor_json as an i64 (KDE: a plain u32). Making them the same changes what one daemon's komorebic state prints, so it is a decision, not a refactor: either a Monitor<P> with an associated MonitorExtra (Windows: the three fields) and MonitorId with a serde adapter per platform, or the extra fields as Options that KDE leaves None and skips when serialising.
• Methods: MonitorInformation has 6 fields on Windows and 4 on KDE; Windows has the two serde helpers, KDE has assign_windows_to_workspaces. The 16 other public methods are common, but load_focused_workspace (Windows hides and restores the workspaces itself, KDE asks the compositor for the desktop) and update_workspaces_globals / update_workspace_globals (Windows pushes the globals into every workspace, KDE into the focused one) differ in behaviour, and need the Platform::show_workspace / hide_workspace hooks of section 3.
• BORDER_ENABLED (Windows) vs BORDER_DRAWN (KDE) are separate statics.

What remains, in order

1. Monitor: decide the field-set question above, add the two workspace hooks to a Platform trait (the first thing in the crate that is a Platform rather than a window), converge the method bodies, then move. The diff after that decision should be a few dozen lines.
2. Workspace: 2314 changed code lines. Needs, besides the hooks, the Windows-only windows_on_show / border_kinds_on_show and the KDE-only reap_invalid_windows, prune_duplicate_windows, adopt_maximized_window, focus_floating_window, focus_previous_floating_window, remove_floating_window as optional Platform hooks or extension traits; the scrolling glue is measured before it moves.
3. WindowManager, then the router and process_event (unchanged from section 3).

7. Classification of the workspace.rs and monitor.rs differences

Method: each file is cut into functions (impl-level and free fns, tests apart), comments and blank lines are dropped, and each function is compared with its namesake on the other side (diff; a changed line counts on both sides). The earlier whole-file figures (workspace 2314, monitor 657) come from one diff of the stripped files, which misaligns after every insertion; per function the picture is much smaller. Classes: (a) cosmetic or ordering drift, (b) same behaviour written differently, (c) a real platform difference (a hook is needed), (d) a feature one side lacks. Measured at the tip of wip-u-core (Container already moved; the Windows tree is kfw's wip-u-kfw).

workspace.rs

	functions	changed lines
identical on both sides (non-test)	36	0
(a) drift	1	31
(b) same behaviour, different text	15	196
(c) platform difference	6	356
(d) feature on one side only	14	270
tests present on both sides	26	71 (all (b): the id rename)
tests only in KDE	20	275

(c) is update (161: Windows adds title bars, stackbars, the animation batch, the scrolling adopt_actual_widths pass and live_resize::is_stepping; KDE clamps layouts to the work area, has the percentage override, scrolling_placed and has_settled), apply_wallpaper (110: Windows writes the wallpaper through WindowsApi and builds the palette theme inline, KDE asks the backend and calls theme_manager::wallpaper_palette), remove_window (41: Windows deletes the border and returns (); KDE returns the Window and unmaximizes it), hide (28: KDE re-runs update for a scrolling workspace whose resize dimensions are set), reintegrate_maximized_window (12: KDE unmaximizes and adds through add_window; Windows loads the focused window) and new_floating_window (4: KDE unmaximizes).

(d) Windows: border_kinds_on_show (34), windows_on_show (10), hwnd_from_exe (26), custom layouts in load_static_config (23), promote_container (5), effective_layout_options (1). KDE: adopt_maximized_window (60), prune_duplicate_windows (40), reap_invalid_windows (33), remove_floating_window (19), focus_floating_window (4), focus_previous_floating_window (4), percentage_within_horizontal_bounds (11), and the scrolling_placed field.

(b) is almost all of: hwnd: isize against window_id: u32 (contains_window, contains_managed_window, container_idx_for_window, container_for_window, focus_container_by_window, is_focused_window_monocle_or_maximized, move_container_to_workspace of the monitor), WindowsApi::foreground_window() / cursor_pos() against backend(), let _ = backend().hide(WindowId::from_hwnd(..)) against window.hide() (also restore, focus, maximize), Option against Result for the title, exe and class (resolve_placement_index, location_from_exe), try_into against into (visible_window_details), new_container_for_window(Window) against (&Window) -> Result<()>, and by value against &self.maximized_window patterns.

monitor.rs

	functions	changed lines
identical (non-test)	8	0
(b)	2	18 (move_container_to_workspace, add_container)
(c)	3	40 (load_focused_workspace, update_workspaces_globals, update_workspace_globals)
(d)	9	113 (the Windows name, device_id and workspace_names fields: new, placeholder, From, focus_workspace, the id serde adapter; Custom layouts in add_container_with_direction; KDE assign_windows_to_workspaces)

What each remaining cluster needs

KDE-side converge revisions (this stack): the (a) and (b) clusters where the Windows form is the better one. What stays, and what kfw does (the list to hand over):

1. id parameter name and type (b): KDE keeps window_id; kfw renames hwnd to window_id and takes the id as the ContainerWindow::Id (isize) so the text is the same.
2. Backend calls inline (b): kfw's backend().hide(WindowId::from_hwnd(..)) and KDE's window.hide() both become ContainerWindow::hide_window() / restore_window() (already in the crate); focus and maximize become Window::focus and Window::maximize on both. kfw: Windows Window needs focus, maximize, unmaximize that call backend(); the Windows result handling (let _ =) moves inside them.
3. Option against Result for title, exe, class, path (b): kfw's Window::title/exe/class/path return Option (as KDE) or both return Result; recommended Option, since Windows never distinguishes the failures.
4. WindowDetails (b): From (KDE) against TryFrom (Windows); kfw makes Windows' infallible (the Err arms were never distinguished).
5. new_container_for_window(Window) (b): KDE adopts the Windows form in this stack.
6. remove_focused_floating_window (b): kfw adopts KDE's two-line form over remove_floating_window (which Windows lacks: add it, it is 19 lines).
7. Error strings of reintegrate_maximized_window (b): KDE's ("no maximized restore index") are right; Windows' copy the monocle ones. kfw adopts KDE's.
8. (c) hooks, to be a WorkspacePlatform trait the workspace is generic over: update needs before_layout / after_layout (Windows: animation batch, INITIAL_CONFIGURATION_LOADED, title bars, stackbar; KDE: clamp, scrolling_placed), place_window(window, rect) (set_rect with the top flag against set_position), and apply_wallpaper; remove_window needs on_window_removed (Windows: border_manager::delete_border) and a decision on the return value (KDE's Window is what callers need: kfw returns it too); hide needs the scrolling step as a hook (after_hide) or moves into KDE only; reintegrate_maximized_window and new_floating_window need unmaximize_window, a no-op on Windows if its native maximize is not undone there (kfw to state which).
9. (d) Windows-only features become optional hooks or extension traits (border_kinds_on_show, windows_on_show, custom layouts) and KDE-only ones likewise (adopt_maximized_window, prune_duplicate_windows, reap_invalid_windows, floating-window focus helpers, scrolling_placed). Custom layouts exist in komorebi-layouts for both; KDE ignores them today (Layout::Custom arms): the question for the owner is whether KDE gains them (a behaviour change) or the shared code keeps #[cfg]-free arms that KDE never reaches.
10. Monitor fields (d): Monitor<P> with #[serde(flatten)] platform: P (decided: the schemars required order of the runtime notification and socket schemas changes, nothing checked in does).

8. Design: the platform hooks of a shared Workspace (not implemented)

Status: design from kfw (Windows side), written against wip-u-core plus the revisions of wip-u-kfw2 (items 1 to 7 of section 7 are done on Windows: window_id, hide_window/restore_window, Window::focus/maximize/unmaximize over backend(), Option lookups, WindowDetails: From, remove_floating_window, the shared error strings). Nothing below is code; no trait exists yet.

8.1 Shape

Workspace<P: WorkspacePlatform> lives in komorebi-core, like Container<W>; P::Window is the ContainerWindow (Copy, with the Id). Windows and KDE implement WorkspacePlatform on a unit struct; the daemon uses the alias type Workspace = komorebi_core::Workspace<WindowsPlatform>. Every hook has a default that does nothing (or the generic behaviour), so a platform lists only its differences. The trait is a generic parameter, not dyn: the calls are in the layout hot path and the platform is fixed at compile time. All hooks take &mut Workspace<Self> or the relevant parts, never the WindowManager, so the layer below window_manager stays independent of it.

The window-facing operations are NOT hooks: focus, maximize, unmaximize, hide_window, restore_window, title/exe/class/path (all Option) are methods the ContainerWindow bound (extended with focus, maximize, unmaximize, title, exe, class, path) requires, which both Window types now have under these names. Hooks are only for behaviour the shared code cannot express with window operations.

8.2 The (c) hooks

Where	Hook	Windows does	KDE does	Default
update start	fn begin_update(&mut self_ws) -> Flow	returns Skip until INITIAL_CONFIGURATION_LOADED; opens the AnimationBatch (a guard returned in Flow::Run(guard), dropped at the end of update, so every move of the pass animates together)	nothing	Run(())
update per layout	fn adjust_layout(&self_ws, layouts: &mut [Rect], work_area: &Rect)	nothing (the borders/padding are already applied by calculate)	clamps every layout to the work area, applies the percentage override	no-op
update, a window gets its rect	fn place_window(&self_ws, window: &P::Window, rect: &Rect, first: bool) -> eyre::Result<()>	title-bar removal or restore (REMOVE_TITLEBARS and the per-window rules), set_position(rect, top) with the top flag set for the maximized and monocle windows, stackbar update for stacks	set_rect, scrolling_placed bookkeeping	backend().set_rect
update end	fn end_update(&mut self_ws)	the scrolling adopt_actual_widths pass when animations are on and the user is not stepping a live resize (live_resize::is_stepping); stackbar redraw	has_settled	no-op
apply_wallpaper	fn apply_wallpaper(&self_ws, monitor: &MonitorId, wallpaper: &Wallpaper) -> eyre::Result<()>	WindowsApi::set_wallpaper plus the palette theme built inline	asks the backend and calls theme_manager::wallpaper_palette	Ok(()) (wallpaper is KDE/Windows only: the trait has no wallpaper operation, D36)
remove_window	fn on_window_removed(&mut self_ws, id: P::Window::Id)	border_manager::delete_border(id)	nothing	no-op
remove_window result	none: the shared version returns eyre::Result<Option<P::Window>>; Windows callers that used () ignore it (KDE's callers need the window to unmaximize it)
hide	fn after_hide(&mut self_ws)	nothing	re-runs update for a scrolling workspace whose resize dimensions are set (the windows would otherwise stay where the hidden layout left them)	no-op
reintegrate_maximized_window, new_floating_window	fn unmaximize_window(w: &P::Window)	none needed: Window::unmaximize is ShowWindow(SW_NORMAL), and update re-places the window afterwards; KDE needs the compositor told. Statement for the owner: Windows does not need to unmaximize there, and does not today (reintegrate_maximized_window loads the focused window; new_floating_window does not unmaximize), so the hook is a no-op on Windows and the shared code calls it in both	window.unmaximize()?	no-op

Flow for begin_update is Option<Guard>-like: enum Flow<G> { Skip, Run(G) } with type UpdateGuard on the trait, () by default. place_window carries the whole per-window part of update; the shared update computes the layouts, walks containers, asks place_window for each window and nothing else. That is where most of the 161 changed lines of update go.

Order of the calls inside update: begin_update -> (maximized/monocle/floating first: place_window) -> for each container: layouts from adjust_layout, place_window per visible window -> end_update. Both platforms already order it this way; the Windows AnimationBatch guard is dropped after end_update (so end_update still sees the batch open, as adopt_actual_widths does today).

8.3 The (d) features

Feature	Where	Becomes
border_kinds_on_show, windows_on_show (Windows)	workspace.rs, read by the border manager and update	an extension trait WorkspaceWindowsExt for Workspace<WindowsPlatform> in the Windows crate: they only read fields (containers, monocle_container, maximized_window, floating_windows), so they need those to be pub, which they are
hwnd_from_exe (Windows)	ContainerExt today	stays an extension trait in the Windows crate (ContainerExt, WorkspaceExt::window_id_from_exe)
custom layouts in load_static_config and add_container_with_direction (Windows)	Layout::Custom arms	stay in shared code behind the Layout enum, which already has Custom in komorebi-layouts; KDE's arms for it return the default layout. Open question for the owner (section 7 item 9): whether KDE should gain custom layouts (a KDE behaviour change)
promote_container, effective_layout_options (Windows, 5 and 1 lines)		shared as they are; KDE gains them unchanged (they are generic)
adopt_maximized_window, prune_duplicate_windows, reap_invalid_windows, percentage_within_horizontal_bounds, the scrolling_placed field (KDE)		a KDE-only extension trait WorkspaceKdeExt; scrolling_placed moves into P::WorkspaceState, an associated type with Default + Serialize-skipping (#[serde(skip)]) that the platform owns
focus_floating_window, focus_previous_floating_window, remove_floating_window's focus step (KDE)		the focus step of remove_floating_window is a hook fn after_floating_removed(&mut self_ws) (no-op on Windows, which does not refocus), the two helpers become shared methods (they are generic)
the Windows-only Monitor fields (name, device_id, workspace_names)	monitor.rs	section 7 item 10: Monitor<P> with #[serde(flatten)] platform: P; P is a MonitorExtra, () on KDE

8.4 What this needs first

1. ContainerWindow (or a WorkspaceWindow: ContainerWindow supertrait) grows focus, maximize, unmaximize, title, exe, class, path. Both Windows have them with the same signatures after the revisions above (focus returns eyre::Result<()>, the others ()/Option).
2. WindowDetails and WindowKind-keyed border data are already plain data; Wallpaper and WorkspaceLayer are in komorebi-protocol.
3. The statics that update reads (REMOVE_TITLEBARS, INITIAL_CONFIGURATION_LOADED, the padding and border globals) are read inside the hooks, not in shared code. WorkspaceGlobals (padding, border offset/width, work-area offset) is plain data and is the only global state the shared Workspace takes, through update_globals as today.
4. border_manager and stackbar_manager stay in the Windows crate and are reached only from place_window, on_window_removed and end_update.

8.5 Order of work and gates

(1) the ContainerWindow extension (pure), (2) move the identical and (b) functions of workspace.rs into the crate generic over the window, keeping the hooks as direct calls under #[cfg] for one revision each (pure move), (3) introduce WorkspacePlatform with the defaults and implement it for both platforms (behaviour-preserving on both), one hook per revision in the order of the table: on_window_removed, apply_wallpaper, place_window, begin_update/end_update, after_hide, unmaximize_window. Gates: Windows commands, workspaces, stacking, scrolling, resize, borders, animation scenarios per hook; KDE fast tier and VM for adjust_layout, after_hide, unmaximize_window.