feat: Niri-style scrolling layout, per-monitor layouts and morphing window motion (2.3.0)

AGENTS.md

@@ -10,12 +10,15 @@ single Rust `.exe` with no installer and no required config. Core hooks:
 
 - **Alt + left-drag** — move any window from anywhere on it (no title bar needed).
 - **Alt + right-drag** — resize from the nearest corner (red bracket marker).
-- **Tiling** — `dwindle` (spiral, default) or `master` layout.
+- **Tiling** — `dwindle` (spiral, default), `master`, `columns`, `grid`,
+  `monocle`, or Niri-style `scrolling` (column strip, off-screen columns
+  parked outside the virtual screen, tabbed columns; `plan/scrolling.md`).
+  Layout is per monitor (`monitor_layouts`).
 - **Up to 10 virtual workspaces**, shared or per-monitor.
 - **Per-monitor status bar** (workspace pills, title, clock, CPU/RAM/battery).
 - **Workspace-switch animation** — overlay compositor: off/slide/spring/fade.
 - **Window glide** — windows animate to their tile slot on open/move/resize/
-  re-tile via a per-window snapshot overlay (off/glide).
+  re-tile/scroll via an overlay of live DWM thumbnails (off/glide).
 - **App launcher** — Alt+Space opens a fuzzy app picker (Start Menu shortcuts),
   hook-driven with no foreground focus. See `plan/launcher.md`.
 - Coloured DWM borders, unfocused dimming, focus-follows-mouse, per-app rules,
@@ -49,7 +52,9 @@ cargo build                    # fast debug build of the whole workspace
 cargo run -p astur             # run the WM from source
 ```
 
-Quit: `Ctrl+C` in the console (runs `restore_all_windows`), or kill the process.
+Quit: tray Quit or `Ctrl+C` in the console (runs `restore_all_windows`: shows
+hidden windows and unparks parked ones), or kill the process (the next launch's
+crash rescue does the same from `~/.astur/rescue.lst`).
 
 Config lives in `%USERPROFILE%\.astur\astur.conf` + `navbar.conf`, both created
 on first run, fully commented, **hot-reloaded on save**.
@@ -58,10 +63,11 @@ on first run, fully commented, **hot-reloaded on save**.
 
 | File | Lines (approx) | What |
 |---|---|---|
-| `crates/astur/src/main.rs` | ~5500 | Everything Win32: hooks, worker threads, manager, bar, animations, launcher, file search, system menu. One big file by design (single TU, fast build). |
-| `crates/astur/src/layout.rs` | ~250 | `dwindle_layout` + `master_stack` geometry. `RECT` type only, no Win32 calls. |
-| `crates/astur-config/src/lib.rs` | ~600 | `Config` struct, documented-default file templates, key/value parser. **No Win32** — pure data, shared with the settings GUI (aliased `config` in the WM). |
-| `crates/astur-settings/` | stub | Settings GUI (egui, WIP). Separate process — a GUI crash can't touch the WM. |
+| `crates/astur/src/main.rs` | ~23800 | Everything Win32: hooks, worker threads, manager, scrolling strip model, bar, tab bars, compositors, launcher, file search, system menu. One big file by preference (see CLAUDE.md; splitting would not change build time). |
+| `crates/astur/src/layout.rs` | ~1300 | Pure tiling geometry (dwindle, master, columns, grid, monocle, scrolling strip: spans, offset clamp, peek/park `classify`, `park_spot`) + tests. `RECT` type only, no Win32 calls. |
+| `crates/astur/src/yasb.rs` | ~800 | GlazeWM-compatible workspace WebSocket API for YASB (loopback only, off by default). |
+| `crates/astur-config/src/lib.rs` | ~2900 | `Config` struct, `LAYOUTS` (the one list of layout names), documented-default file templates, key/value parser. **No Win32** — pure data, shared with the settings GUI (aliased `config` in the WM). |
+| `crates/astur-settings/` | ~1400 | Settings GUI (egui), shipped. Separate process — a GUI crash can't touch the WM. |
 | `Cargo.toml` (root) | — | `[workspace]` manifest + release profile. WM deps live in `crates/astur/Cargo.toml`. |
 
 `main.rs` is large but sectioned with `// ====` banners. Use the function map
@@ -70,22 +76,38 @@ on first run, fully commented, **hot-reloaded on save**.
 ## Threads (mental model)
 
 The process is a set of single-purpose threads talking over `Mutex`/`Condvar`
-queues. Keep it that way — do not move work onto the hook threads.
-
-- **Hook threads** (`mouse_proc`, `keyboard_proc`) — run inside `WH_MOUSE_LL` /
-  `WH_KEYBOARD_LL`. Must return fast. They push to queues; they do not do work.
-  `ANY_DRAG`/`ALT_DOWN` atomics let them early-out without locking.
-- **Manager loop** (`manager_loop` / `Manager`) — owns all window/workspace state.
-  Drains the command queue (`CMDQ`). All `SetWindowPos`/tiling/switching here.
-- **Position worker** (`position_worker`) — applies drag move/resize off the hook
-  so a slow app's `SetWindowPos` can't stall input.
+queues. Keep it that way — do not move work onto the hooks (main thread).
+
+- **Main thread** — installs and runs the hooks: `mouse_proc` / `keyboard_proc`
+  (`WH_MOUSE_LL` / `WH_KEYBOARD_LL`) and `win_event_proc` (out-of-context
+  WinEvents). Hooks must return fast: push a `Cmd`, do no work, no lock without
+  an atomic guard (`ANY_DRAG`/`ALT_DOWN`/`SCROLLMON_N` let them early-out).
+  Also owns the bar windows, the tray and the scrolling layout's tab-bar
+  windows (`astur_tabs`, synced from the manager's `TAB_SNAPSHOT` by
+  `tab_bars_sync`; clicks push `Cmd::TabClick`, nothing places windows).
+- **Manager loop** (`manager_loop` / `Manager`) — owns all window/workspace/
+  strip state. Drains the command queue (`CMDQ`). All `SetWindowPos`/tiling/
+  switching/parking here, live Alt-drag placement included (`place_drag_frame`).
 - **Transition worker** (`transition_worker` / `run_transition`) — owns the
   workspace-switch overlay, pumps its own message loop, GDI-composites frames
   (fade: DWM blends a second, layered overlay instead).
-- **Glide worker** (`glide_worker` / `run_window_glide`) — same pattern for the
-  per-window move/open/close/resize glide overlay.
+- **Motion worker** (`glide_worker` / `run_window_glide`, thread "glide") —
+  window motion overlay (move/open/close/reflow/scroll): live DWM thumbnails
+  of already-placed windows over the wallpaper, re-aimed in place while it
+  runs (`retarget_glide`). Owns its overlay, pump and every thumbnail.
+- **Wallpaper capture** (`wallpaper_capture_worker`) — renders the wallpaper
+  backdrop for both compositors (PrintWindow of the wallpaper window only).
+- **Cold-snapshot worker** (`cold_worker`) — PrintWindows cold parked tiles
+  (blank DWM surface: hidden, minimised, or never on screen since shown) into
+  the `COLD` cache so the motion can draw them. Besides the wallpaper capture,
+  the only thread that PrintWindows (never the manager, a compositor or a
+  hook). A hung app may block it; nothing waits on it.
 - **Stats worker** (`stats_worker`) — polls CPU/RAM/battery ~2s for the bar.
-- **Focus-follow worker**, **config watcher**, **bar windows** — as named.
+- **Disk writers** (`state_worker`, `mru_worker`, `rescue_worker`) — the
+  manager only fills a latest-wins slot; the disk I/O (state, launcher MRU,
+  `rescue.lst`) runs here, so a slow disk never delays a command.
+- **Focus-follow worker**, **config watcher**, **launcher**, **sysmenu**,
+  **icon/file-search workers**, **IPC**, **YASB**, **hook watchdog** — as named.
 
 ## Conventions
 
@@ -97,7 +119,9 @@ queues. Keep it that way — do not move work onto the hook threads.
 - Cosmetic threads get bitmap/rect data by **single-owner hand-off, never
   shared** — a handle the owner gives up, moved rather than copied (the
   incoming workspace snapshot is taken out of the cache; the outgoing capture
-  goes to the transition worker and is handed back as the snapshot). Exactly
+  goes to the transition worker and is handed back as the snapshot; a cold
+  window's snapshot is taken out of its cache into the motion request and
+  freed by the glide worker). Exactly
   one thread owns, and frees, each bitmap at any moment; the owned `Bmp` type
   (no `Clone`) enforces it for snapshots. Deselect, then `GdiFlush`, before
   every hand-off.
@@ -107,6 +131,8 @@ queues. Keep it that way — do not move work onto the hook threads.
 ## Where to go next
 
 - `plan/architecture.md` — deeper component + data-flow notes.
+- `plan/scrolling.md` — scrolling layout spec + contract: keys, config,
+  geometry, peek/park, safety, manual test checklist.
 - `plan/animations.md` — animation design: desktop-switch modes (off/slide/spring/
   fade) and the honest analysis of window open/close/move/resize animation.
 - `plan/win32-reference.md` — APIs used, doc links, gotchas (slow/buggy calls).