feresaria/docs/ferese-window-manager-spec.md

# Ferese Window Manager Specification

Status: Draft for implementation  
Target: Ferese v0 core and desktop-tier roadmap
Language: Rust  
Display protocol: Wayland

## 1. Purpose

Ferese is a Wayland tiling compositor for a conventional, keyboard-friendly
desktop. It combines predictable window management with compositor-owned rounded
geometry, shadows, animation, transparency, and semantic surface materials.

This document is the implementation source of truth for Ferese v0 and records
the gated desktop-tier roadmap. The terms **MUST**, **MUST NOT**, **SHOULD**,
**SHOULD NOT**, and **MAY** are normative within the tier being specified.

## 2. Product principles

1. Window-management behavior is predictable and familiar.
2. The compositor owns composition effects; clients request semantic intent.
3. Core state has one authoritative representation.
4. Rendering and animation never block input.
5. Optional shell processes may fail without terminating the compositor.
6. Effects degrade gracefully when performance requires it.
7. The nested compositor is the primary development environment.
8. Security-sensitive operations are unavailable to untrusted clients.

### 2.1 Companion specification ownership

Ferese uses three normative documents with non-overlapping ownership:

| Concern | Normative owner |
| --- | --- |
| compositor mechanism, Wayland policy, focus, layout, rendering, IPC, security | this document |
| shell interaction, visibility, launcher, notifications, DND, shell focus | `ferese-shell-design.md` |
| colors, semantic surface tokens, typography, icons, and exact shell component geometry | `ferese-theme-ui-spec.md` |

The shell specification MUST reference visual tokens instead of duplicating
pixel, radius, color, shadow, blur, or typography values. The theme/UI
specification MUST NOT redefine focus, fullscreen, workspace, launcher,
notification, or security behavior.

If companion documents conflict, the owner in this table is authoritative for
that concern.

## 3. Scope

### 3.1 v0 core requirements

Ferese v0 is the smallest independently usable native-Wayland release. It MUST
provide:

- native Wayland compositing;
- automatic and manually adjustable tiling;
- floating and fullscreen windows;
- multiple workspaces and outputs;
- keyboard and pointer input;
- native Wayland clipboard, primary selection, and drag-and-drop;
- client-side and server-side decoration negotiation;
- rounded clipping, borders, shadows, and transparency;
- frame-timestamp-driven window and workspace animations;
- damage-aware rendering;
- validated live configuration reload;
- authenticated local IPC and a command-line client;
- direct application launching;
- standard layer-shell support under the policy in Section 8;
- a direct DRM/KMS session; and
- the required native protocol baseline in Section 8.1.

The completed v0 MUST support routine native-Wayland software-development work
without regular compositor restarts. The graphical Ferese shell is not required
for basic window management or application launching.

### 3.2 Desktop tier

The desktop tier builds on the v0 core and includes:

- semantic surface materials with glass, translucent, and solid rendering;
- the Ferese top bar, overview, launcher UI, workspace UI, OSD, and notifications;
- the graphical settings application;
- portal-backed screenshots and screen sharing; and
- X11 compatibility through `xwayland-satellite` unless an architectural
  decision record selects another design.

These features MUST NOT delay the v0 core. Each MUST degrade or fail without
terminating the compositor or invalidating managed-window state.

### 3.3 Non-goals

The following are outside v0:

- a file manager, display manager, or lock screen;
- network, Bluetooth, or package-management UI in v0 or the initial desktop-tier shell;
- a general plugin or scripting system, or arbitrary CSS/component-replacement theme engine;
- desktop widgets;
- advanced dynamic layout algorithms;
- exhaustive support for every Wayland protocol or toolkit edge case; and
- pixel-for-pixel imitation of another operating system.

Ferese MAY display a configured color or image, but a standalone wallpaper
daemon is not part of v0.

## 4. Architecture

### 4.1 Processes

| Executable | Responsibility |
| --- | --- |
| `ferese` | Compositing, policy, input, scene construction, and rendering |
| `ferese-shell` | Top bar, overview controls, launcher, workspace UI, notifications, and OSD |
| `ferese-settings` | Graphical configuration editor |
| `feresectl` | Command-line IPC client |

`ferese` MUST remain usable if another Ferese process exits. Shell and settings
code MUST NOT run inside the compositor.

```text
Wayland clients (plus optional X11 satellite)
          |
          v
  protocol adapters
          |
          v
 authoritative core state
          |
          +----> layout targets
          +----> animation state
          |
          v
      scene graph
          |
          v
 damage-aware renderer
          |
          v
 nested window or DRM/KMS output
```

Protocol handlers MUST translate requests into domain operations. Business
logic MUST NOT accumulate in Smithay callbacks.

### 4.2 Technology baseline

The initial implementation uses Rust, Smithay, calloop, Smithay's GLES renderer,
`glow`, targeted GLSL shaders, DRM/KMS, GBM, EGL, dma-buf, libinput, xkbcommon,
libseat, serde, TOML, serde JSON, clap, tracing, and GPUI.

Dependencies MAY change when an architectural decision record explains the
reason and migration impact.

### 4.3 Repository layout

```text
ferese/
|-- Cargo.toml
|-- crates/
|   |-- ferese-core/
|   |-- ferese-layout/
|   |-- ferese-render/
|   |-- ferese-animation/
|   |-- ferese-config/
|   |-- ferese-ipc/
|   |-- ferese-protocols/
|   `-- ferese-shell-protocol/
|-- compositor/
|-- shell/
|-- settings/
|-- feresectl/
`-- protocols/
    |-- ferese-effects-v1.xml
    `-- ferese-shell-v1.xml
```

`ferese-layout` MUST be pure Rust and MUST NOT depend on Smithay or Wayland
objects.

### 4.4 Domain operations

Wayland callbacks, input handlers, IPC handlers, configuration reload, and shell
requests MUST enter core policy through explicit domain operations rather than
mutating unrelated managers directly. A representative shape is:

```rust
pub enum Command {
    Focus(Direction),
    Move(Direction),
    Resize(Direction, f32),
    SwitchWorkspace(WorkspaceId),
    MoveToWorkspace(WindowId, WorkspaceId),
    ToggleFloating(WindowId),
    ToggleFullscreen(WindowId),
    SetConfig(ConfigChange),
}

pub enum Event {
    WindowMapped(WindowMapData),
    WindowUnmapped(WindowId),
    OutputConnected(OutputDescriptor),
    OutputDisconnected(OutputId),
    SurfaceCommitted(SurfaceCommit),
}

pub struct WindowMapData {
    pub window: WindowId,
    pub surface: SurfaceId,
    pub app_id: Option<String>,
    pub title: Option<String>,
    pub parent: Option<WindowId>,
    pub requested_fullscreen: bool,
    pub constraints: SizeConstraints,
}
```

A command or event is applied as one state transaction. Commands express
requested policy changes; events describe facts received from protocol or
backend adapters and include the metadata needed to apply policy. Neither type
MUST be used for emitted notifications.

The transaction MUST either
complete with all Section 5 invariants restored or leave authoritative state
unchanged. Rendering, protocol configure requests, IPC events, and persistence
are consequences emitted after the state transition; they MUST NOT become a
second source of policy state.

### 4.5 Threading and execution

The calloop thread owns the Wayland display, input dispatch, authoritative
`FereseState`, policy transactions, configure scheduling, and scene publication.
No other thread may mutate compositor state or Wayland objects.

Shader compilation, image decoding, configuration file I/O, IPC serialization,
and other bounded background work MAY run on workers. Workers receive immutable
snapshots or owned messages and return results through bounded channels. The
calloop thread validates each result against current identifiers and generations
before applying it. Rendering MAY run on the calloop thread initially; if moved
to a render thread, scene snapshots and buffer ownership MUST cross an explicit
handoff and never require input dispatch to wait for GPU completion.

Blocking filesystem, process-wait, D-Bus, portal, and client IPC operations MUST
NOT run on the calloop thread.

## 5. Authoritative state

The compositor MUST maintain one state root:

```rust
pub struct FereseState {
    pub outputs: OutputManager,
    pub workspaces: WorkspaceManager,
    pub windows: WindowManager,
    pub seat: SeatState,
    pub layout: LayoutManager,
    pub animations: AnimationManager,
    pub config: Config,
}
```

Smithay objects SHOULD remain behind adapter types rather than become the domain
model.

### 5.1 Identifiers

Outputs, workspaces, windows, layout nodes, and the logical seat MUST have stable
internal identifiers. An identifier MUST NOT be reused during one compositor
lifetime.

```rust
pub struct WindowId(u64);
pub struct WorkspaceId(u64);
pub struct OutputId(u64);
pub struct NodeId(u64);
pub struct SeatId(u64);
pub struct SurfaceId(u64);
```

Ferese v0 exposes exactly one logical seat. Multiple physical keyboards, mice,
and touch devices MAY feed that seat. Multi-seat policy is outside v0 and MUST
NOT be implied by the domain model.

### 5.2 Windows

```rust
pub struct Window {
    pub id: WindowId,
    pub app_id: Option<String>,
    pub title: Option<String>,
    pub workspace: WorkspaceId,
    pub placement: WindowPlacement,
    pub fullscreen: bool,
    pub constraints: SizeConstraints,
    pub urgent: bool,
    pub material: WindowMaterial,
}

pub enum WindowPlacement {
    Tiled,
    Floating { rect: RectF },
}
```

Fullscreen is a presentation state layered over the preserved tiled or floating
placement. Entering fullscreen MUST NOT remove a tiled window from its layout
tree or a floating window from its floating list. At most one window may be
fullscreen on a workspace. While fullscreen is active, that window is the sole
normal managed-window content presented for the workspace, although permitted
shell overlays and popups may still appear. Leaving fullscreen restores the
preserved placement without reconstructing it.

A window MUST NOT independently store an output. Its output is derived from its
workspace, preventing stale ownership after workspace migration. Authoritative
keyboard focus belongs to `SeatState` and MUST NOT be duplicated on every
window or workspace. Layout hierarchy MUST NOT be embedded in `Window`.

### 5.3 Workspaces

```rust
pub struct Workspace {
    pub id: WorkspaceId,
    pub name: String,
    pub output: Option<OutputId>,
    pub root: Option<NodeId>,
    pub floating: Vec<WindowId>,
    pub last_focused: Option<WindowId>,
}

pub struct SeatState {
    pub id: SeatId,
    pub keyboard_focus: FocusTarget,
    pub pointer_focus: Option<SurfaceId>,
    pub focused_output: Option<OutputId>,
    pub focused_workspace: Option<WorkspaceId>,
}

pub enum FocusTarget {
    None,
    Window(WindowId),
    Shell(SurfaceId),
}
```

`Workspace::last_focused` is restoration/history state only. It MUST NOT be
interpreted as current keyboard focus.

These invariants MUST hold after every state transaction:

1. Every managed window belongs to exactly one workspace.
2. Every attached workspace belongs to exactly one connected output; only a
   workspace awaiting an output may contain `None`.
3. An output exposes exactly one active workspace.
4. A window with `WindowPlacement::Tiled` appears exactly once in its workspace
   tree and not in the floating list.
5. A window with `WindowPlacement::Floating` appears exactly once in the
   floating list and not in the tree.
6. Fullscreen does not alter the window's underlying placement membership.
7. A `FocusTarget::Window` refers to a managed window on
   `seat.focused_workspace`; a `FocusTarget::Shell` refers to a live, authorized
   interactive shell surface.
8. `Workspace::last_focused`, when present, refers to a window belonging to that
   workspace.
9. At most one window is fullscreen on a workspace at a time.

Workspace migration MUST be atomic. If an output disappears, its workspaces move
to a deterministic remaining output. If none remains, they stay detached until
an output appears.

Numeric workspace names are unbounded, but the default bindings directly address
`1` through `9` and create them lazily. Named workspaces MAY be added after v0.

### 5.4 Focus semantics

The single v0 seat owns authoritative keyboard focus, pointer focus, focused
workspace, and focused output. A workspace stores only `last_focused` so focus
can be restored when that workspace becomes active.

When switching to a workspace that is already visible on another output, Ferese
MUST focus that output and workspace instead of moving or swapping the workspace.
Explicit workspace-move commands are responsible for relocating workspaces.

Mapping a normal application while another window is fullscreen MUST preserve
the fullscreen window and place the new window into the underlying layout or
floating list without revealing or focusing it. An urgent indication MAY be
shown. A transient with a valid parent is floating by default, centered over and
constrained to the parent's visible output, and follows the parent's workspace.
Activation policy, not mapping alone, determines whether a transient receives
focus.

Window rules MAY match normalized `app_id`, title, and transient metadata and
set initial workspace, floating state, dimensions, or fullscreen state. Rules
MUST be evaluated deterministically before insertion. Title matching SHOULD be
avoided when a stable `app_id` exists.

### 5.5 Application identity and launch association

Ferese exposes normalized application identity to trusted shell clients without
making application identity part of layout policy.

```rust
pub struct ApplicationIdentity {
    pub desktop_id: Option<String>,
    pub app_id: Option<String>,
    pub startup_wm_class: Option<String>,
}

pub struct LaunchAssociation {
    pub id: LaunchId,
    pub desktop_id: Option<String>,
    pub activation_token: Option<String>,
    pub child_pid: Option<u32>,
    pub started_at: Instant,
}
```

Application identity resolution MUST prefer explicit desktop-entry association,
then normalized Wayland `app_id`, then `StartupWMClass`/X11 class metadata when
available. Ferese MUST NOT guess that unrelated strings are equivalent merely
because they are similar. Case and an optional `.desktop` suffix MAY be
normalized only where desktop-entry semantics make that comparison unambiguous.

A shell-initiated launch MUST be tracked until the resulting window is
associated or the launch expires. XDG activation information is the preferred
association; process ancestry and normalized application identity MAY be used as
fallbacks. The association exists to drive shell state such as `launching`,
`running`, and focus. It MUST NOT bypass ordinary window rules or workspace
policy.

## 6. Layout

```rust
pub enum Node {
    Window(WindowId),
    Split {
        axis: Axis,
        ratio: f32,
        first: NodeId,
        second: NodeId,
    },
    Stack {
        children: Vec<NodeId>,
        active: usize,
    },
}

pub enum Axis {
    Horizontal,
    Vertical,
}
```

Split ratios MUST be finite and clamped so descendants satisfy their minimum
sizes where possible. If all constraints cannot be met, the focused window takes
priority and the conflict MUST be logged.

The engine consumes a layout tree, usable logical geometry, size constraints,
and tiling configuration. It returns a deterministic `WindowId -> RectF` map and
constraint warnings. Identical input MUST produce identical output.

The following tree invariants MUST hold after every layout transaction:

1. The tree is acyclic and every reachable node has exactly one parent except
   the root, which has none.
2. Both children of a split exist and are distinct.
3. A stack contains at least two children and its `active` index is in bounds.
4. Removing a child collapses a one-child split or stack into its remaining
   child; removing the last child removes that branch.
5. Every tiled window is represented by exactly one reachable leaf and every
   reachable window leaf refers to a tiled window in the same workspace.
6. The focused leaf inside a stack is the active child's recursively focused
   window; directional operations enter a stack through its active child.

### 6.1 Automatic insertion

1. The first tiled window becomes the root.
2. A later window splits the focused leaf.
3. For `default_split = "automatic"`, use a horizontal split when the focused
   rectangle is wider than tall and a vertical split otherwise.
4. The new window becomes focused after its first mapped commit.

### 6.2 Required operations

Ferese MUST support directional focus, movement and resizing; explicit split
direction; floating and fullscreen toggles; tiled-divider resize; floating
move/resize; and tiled drag-and-drop.

Drag targets are `left`, `right`, `top`, `bottom`, and `center`. A drag MUST show
a live preview. Center creates or joins a stack; an edge creates a split.

### 6.3 Gaps

Gaps belong exclusively to `[tiling]`. `inner_gap` separates tiles and
`outer_gap` separates tiles from output bounds. With `smart_gaps = true`, a lone
tiled window has no outer gap.

## 7. Geometry and animation

Ferese MUST distinguish buffer, surface-local, logical-output, and physical
coordinates. Layout and input policy use logical coordinates. Rendering performs
physical conversion. Fractional scaling MUST avoid cumulative rounding errors
between adjacent tiles. The renderer MUST snap shared logical boundaries once
per output and derive adjacent physical rectangles from those same snapped
edges; it MUST NOT independently round each tile's origin and size.

A managed window has three geometry domains that MUST remain distinct:

1. **logical geometry:** the authoritative layout destination;
2. **visual geometry:** where the compositor currently presents the window while
   an animation is in progress; and
3. **client geometry:** the most recently configured and committed client content
   size.

A representative model is:

```rust
pub struct AnimatedRect {
    pub current: RectF,
    pub target: RectF,
    pub velocity: RectF,
}

pub struct ClientGeometry {
    pub last_configured_size: Size<i32>,
    pub committed_size: Size<i32>,
}

pub struct WindowGeometry {
    pub visual: AnimatedRect,
    pub client: ClientGeometry,
}
```

`visual.target` is the authoritative logical layout rectangle. The target becomes
authoritative immediately after the state transaction even if the client has not
yet committed a buffer matching its new size.

For a non-interactive layout transition Ferese MUST:

1. compute and store the final target geometry;
2. send a configure for the final client size rather than one configure per
   animation frame;
3. continue presenting the most recent committed client content while visual
   geometry interpolates toward the target;
4. map pointer coordinates through the inverse visual transform before
   delivering surface-local input; and
5. accept a newly committed target-sized buffer without restarting the visual
   transition.

The renderer MAY use a short-lived snapshot of the previously committed content
to avoid a visible source-size discontinuity. Whether using a live committed
buffer or snapshot, client content MUST remain aligned with the visual geometry
used for hit testing.

During a non-interactive resize, committed content is scaled uniformly to cover
the visual content box and clipped to that box, anchored at its top-left content
origin. Ferese MUST NOT expose uninitialized regions. When a matching commit
arrives it replaces the scaled source without restarting the animation. A commit
is matching when its acknowledged configure and effective buffer geometry match
the requested client size after scale and transform.

If a client has not acknowledged and committed the final configure within 500
ms, Ferese MUST stop waiting for visual completion, retain the target layout,
and continue presenting the latest valid content using the same scale-and-clip
policy. The timeout is diagnostic rather than permission to send repeated
configures. A client commit larger than its assigned tile is clipped to the
tile; it MUST NOT overlap adjacent managed windows or change layout geometry.

During an interactive resize, configure events MAY follow pointer motion subject
to normal coalescing and client responsiveness. Keyboard navigation MUST use the
target layout topology, not transient visual geometry.

When animation is disabled or reduced motion is active, `visual.current` snaps
to `visual.target`. Geometry uses spring animation; opacity, dimming, blur
intensity, and overlays use bounded easing. Updates MUST use presentation or
monotonic frame timestamps and MUST NOT assume a fixed refresh rate.

The default geometry spring uses mass `1.0`, stiffness `320.0`, and damping
`36.0`, which is approximately critically damped. Geometry defaults MUST NOT
overshoot shared tile boundaries. User-configured underdamped geometry springs
MAY overshoot numerically, but their rendered content remains clipped to the
animated allocation and MUST NOT cover adjacent windows.

Animations MUST stop within configured tolerances. Hidden animations SHOULD stop
requesting frames. Opening, closing, or moving a window MUST never block input.

## 8. Wayland behavior

### 8.1 Required native protocols

Before the native desktop is usable, Ferese MUST support the following core
protocols and widely deployed extensions:

- compositor, subcompositor, shared memory, and outputs;
- xdg-shell;
- xdg-activation;
- seats, keyboard, pointer, and available touch devices;
- data-device clipboard and drag-and-drop;
- primary selection;
- xdg-decoration;
- relative pointer and pointer constraints;
- presentation timing;
- viewporter and fractional scaling;
- layer-shell;
- screencopy with the capture authorization policy from Section 13;
- cursor-shape-v1;
- text-input-v3 and input-method-v2;
- keyboard-shortcuts-inhibit-v1;
- idle-notify-v1 and idle-inhibit-v1;
- xdg-foreign-v2;
- single-pixel-buffer-v1; and
- Linux dma-buf where supported.

Layer-shell is a public standard role and MUST NOT require a Ferese private
capability. Ferese MUST enforce exclusive-zone, focus, namespace, and layer
policy so ordinary panels, launchers, and notification daemons can use it
without receiving unrestricted compositor authority. Input-method access,
screencopy, and shortcut inhibition MUST use explicit user/session policy;
binding a public global alone MUST NOT silently grant capture or persistent
keyboard interception.

Virtual input and session-lock MAY be added after their security and failure
policies are specified. Portal integration is not a Wayland protocol: the
desktop tier MUST separately provide an XDG Desktop Portal backend and PipeWire
integration for interactive screenshots and screen sharing.

### 8.2 Decorations

Ferese MUST support client-side decorations. If a client negotiates server-side
decorations, Ferese MUST provide usable move, resize, and close interactions.
Shadows, masks, and focus borders are compositor effects and may apply in either
mode.

### 8.3 XWayland

The desktop tier SHOULD use `xwayland-satellite`, launched on demand, so X11
clients become ordinary xdg-shell toplevels from Ferese's perspective. The
layout engine and `Window` abstraction MUST remain protocol-agnostic. Clipboard
and primary-selection interoperability depend on the corresponding public
Wayland protocols remaining available to the satellite.

An embedded X11 window manager requires an architectural decision record and
MUST justify the additional selection, focus, stacking, and override-redirect
policy. Tests MUST cover X11 menus, dialogs, games, and applications that request
absolute positioning; the satellite approach reduces compositor complexity but
does not guarantee every X11 positioning convention.

## 9. Scene and rendering

Ferese MUST build an explicit scene from authoritative state and current
animation values. Nodes SHOULD cover surfaces, popups, decorations, shadows,
masks, borders, materials, shell UI, drag icons, and cursors.

Scene order is background, windows back-to-front, shell/overlays, drag icons,
then cursor. Within a window, the shadow is behind clipped background and client
content; the border is above. Rounded clipping MUST be established before
drawing clipped content or through an equivalent offscreen pass. Client buffers
MUST NOT be modified to implement effects.

Rendering MUST be damage-driven. Damage includes commits, movement, animation,
shadows, borders, material invalidation, shell, cursor, and output changes.
Moving or removing a node MUST damage both old and new bounds. Expansion MUST
include shadow, blur-kernel, and sampling extents.

Direct scanout SHOULD be possible when one compatible fullscreen surface covers
an output and no transform, overlay, capture, conversion, or effect requires
composition.

Rounded corners use a GPU mask or equivalent. Fullscreen windows use zero radius.
Shadows SHOULD use analytic shaders, cached textures, or reduced-resolution
intermediates rather than full-resolution per-frame blur.

## 10. Material system

This section specifies compositor support for desktop-tier semantic surfaces. It
is not a v0 release gate. Theme token values and exact component geometry belong
to `ferese-theme-ui-spec.md`.

Initial semantic surface roles are:

```text
surface.panel
surface.panel_elevated
surface.popover
surface.menu
surface.notification
surface.hud
surface.modal
```

Clients request semantic roles rather than raw shader values.

The compositor resolves each role through the active material style:

```rust
pub enum MaterialStyle {
    Glass,
    Translucent,
    Solid,
}
```

`ferese-effects-v1` is private to trusted Ferese components. It MAY set or clear
a semantic surface role. It MUST NOT expose shader code, unrestricted capture,
arbitrary renderer state, or unbounded effect values. Its global MUST be
advertised only to Wayland clients granted the `effects` capability by the
private-client mechanism in Section 13.

For `Glass`, the compositor-owned rendering pipeline is:

```text
lower scene content
  -> capture expanded region
  -> downsample
  -> blur
  -> upsample
  -> saturation and brightness
  -> tint and optional noise
  -> semantic surface foreground
```

Blur MUST exclude the requesting surface and all content above it. Sampling
bounds MUST include the kernel radius.

For `Translucent`, the compositor applies semantic tint and alpha without
backdrop capture. For `Solid`, the compositor uses an opaque semantic surface
color. Changing material style MUST NOT change component geometry, focus, input
regions, layer-shell roles, or shell behavior.

A blur cache entry MUST identify its output and scale, visible and sample
regions, semantic role and resolved material parameters, contributing
lower-layer generations, and result texture. Changes to content, stacking,
geometry, scale, transform, resolved material, workspace, or output MUST
invalidate affected entries. A global generation MAY be used initially;
region-aware invalidation SHOULD replace it before performance tuning is
complete.

### 10.1 Built-in visual profile

The desktop tier provides one restrained Ferese visual language with glass,
translucent, and solid profiles. Exact values for colors, radii, shadows,
typography, spacing, and material parameters are normative only in
`ferese-theme-ui-spec.md`.

Focused and foreground content MUST remain distinguishable without transparency.
Blur, borders, and shadows SHOULD establish hierarchy rather than compete for
attention. Settings, top bar, overview chrome, notifications, launcher, popovers,
and OSD MUST consume the same semantic surface and spacing tokens.

## 11. Shell and overview

This section specifies compositor-facing desktop-tier shell behavior. Detailed
interaction is normative in `ferese-shell-design.md`; visual tokens and exact
component geometry are normative in `ferese-theme-ui-spec.md`.

`ferese-shell` owns the top bar, overview controls, launcher, workspace UI,
notifications, and volume and brightness OSD. Screenshot UI MAY be added after
capture policy and implementation are complete. The shell uses a
capability-scoped private Wayland connection plus authenticated IPC.

Ferese deliberately has no persistent dock or bottom application bar.

Overview MUST NOT require copying each managed window into the shell process.
The compositor owns the live window presentation and enters an overview scene
mode in which existing window scene nodes receive temporary visual transforms.
`ferese-shell` supplies controls such as labels, selection affordances,
workspace UI, and later search.

The overview binding is `Super+Tab`. Entering overview MUST animate windows from
their current visible geometry into overview geometry. Pointer and keyboard
selection MUST target the compositor-owned live window nodes. Dismissing
overview MUST animate those same nodes back to the current layout targets.
Workspace switching from overview MUST obey Section 5.4.

### 11.1 Public layer-shell

`ferese-shell` MUST use standard layer-shell for the top bar, launcher,
workspace UI, notifications, popovers, and OSD surfaces. Such surfaces are not
managed application windows and MUST NOT enter tiling, workspace focus history,
or normal application task switching.

Layer-shell is a public standard role and remains available to ordinary
third-party panels, launchers, notification daemons, and wallpapers under
Section 8 policy. Binding layer-shell MUST NOT grant Ferese-specific metadata,
overview control, capture, virtual input, or semantic-surface capability.

The compositor enforces layer, exclusive-zone, keyboard-interactivity,
input-region, namespace, and output policy.

### 11.2 Top bar, fullscreen, and reservation

The Ferese top bar is the only persistent Ferese shell surface that reserves
workspace space.

Fullscreen is a presentation state over the preserved underlying workspace
layout. Entering fullscreen MUST hide the Ferese top bar visually without
changing the underlying workspace usable layout region. Leaving fullscreen MUST
restore the bar without reconfiguring hidden tiled windows merely because the
bar reappears.

A temporary top-bar reveal over fullscreen MUST use overlay presentation and
`exclusive_zone = 0`. It MUST NOT resize the fullscreen client or alter the
underlying workspace layout.

If `ferese-shell` disconnects unexpectedly, the compositor SHOULD retain the
last valid Ferese-owned top-bar reservation for a short bounded grace period.
If the shell reconnects with a compatible reservation before the lease expires,
tiled windows MUST NOT reflow. If the grace period expires, Ferese removes the
reservation and performs at most one ordinary layout reflow.

### 11.3 Private shell control protocol

`ferese-shell-v1` is a private control and metadata protocol. It MUST NOT
duplicate layer-shell roles, exclusive zones, or general surface placement.

Its initial responsibilities are limited to:

```text
managed-window list and lifecycle
application identity metadata
focused and urgent state
activate managed window
request close
enter / exit overview
select overview window / workspace
```

The protocol requires the `shell-control` capability from Section 13. Requests
MUST be validated against current stable identifiers and flow through the same
domain operations as keyboard, pointer, and IPC actions.

### 11.4 Launcher and application launching

The initial Ferese launcher is apps-only. Its default binding is `Super+Space`.
It discovers XDG desktop applications, searches application names and normalized
application identity, and launches selected applications.

The initial search placeholder is:

```text
Search apps…
```

Files, recents, settings, and command providers MAY be added later. The shell
MUST NOT display dead tabs for unavailable providers.

Before launch, the shell MUST obtain an xdg-activation token tied to the
triggering user interaction and make the token available to the child. The child
receives the public Wayland display and normal session environment. It MUST NOT
inherit a private Wayland descriptor, IPC capability, or bearer secret.

A private descriptor deliberately inherited when the compositor starts a trusted
component is the sole exception during that component's initial exec; the
component MUST mark it close-on-exec before it can launch any child.

### 11.5 Shell focus and modals

Interactive shell surfaces MAY receive `FocusTarget::Shell`. The persistent top
bar SHOULD remain non-keyboard-interactive during ordinary use.

The launcher receives keyboard focus while open and MUST restore the previous
valid managed-window focus on dismissal where possible. Interactive popovers and
modals follow the same restoration rule.

A shell modal is appropriate only for destructive confirmation,
security-sensitive confirmation, or an irreversible shell action. While a modal
is active, the compositor presents a scrim and directs keyboard focus to the
modal. Input outside the modal is consumed by the scrim and MUST NOT reach
managed applications.

Destroying a shell surface or disconnecting the shell MUST never leave a dead
`FocusTarget::Shell`.

Ferese does not ship a polkit authentication agent in the initial desktop tier.
System authentication requiring polkit uses an external agent until a separate
authentication-agent security specification exists.

### 11.6 Notifications and Do Not Disturb

`ferese-shell` MUST implement the standard `org.freedesktop.Notifications` D-Bus
service for basic notifications. The desktop tier MUST support summary, body,
icon metadata, expiry, replacement, close, actions, and urgency metadata.

Notification content is untrusted: markup, image paths, and action identifiers
MUST be parsed and rendered without command execution.

When Do Not Disturb is disabled, eligible notifications MAY create transient
toasts and enter notification history. When Do Not Disturb is enabled, normal
transient toasts are suppressed but notifications still enter history and
unread state still updates. A future explicitly defined critical-urgency policy
MAY bypass DND; application-name heuristics MUST NOT.

Network and Bluetooth control UI are outside the initial desktop-tier shell and
MUST NOT appear as required or placeholder controls.

If the shell restarts, it MUST reacquire the notification service and reconstruct
shell state without affecting managed windows.

## 12. Configuration

The primary file is `$XDG_CONFIG_HOME/ferese/config.toml`, falling back to
`~/.config/ferese/config.toml`.

Configuration has one authoritative representation. Namespace ownership is:

```text
[theme.*]         visual tokens/material mapping   ferese-theme-ui-spec.md
[shell.*]         shell behavior                   ferese-shell-design.md

[animations]      compositor animation policy      this document
[tiling]          layout policy                    this document
[input]           input policy                     this document
[commands]        launch command vectors           this document
[[bindings]]      compositor bindings              this document
[[window_rules]]  window placement rules           this document
```

There is no separate legacy visual namespace. Blur, opacity, radii, shadows,
surface colors, typography, and shell component geometry belong only to
`[theme.*]`.

Representative core configuration:

```toml
[animations]
enabled = true
reduced_motion = false
speed = 1.0

[animations.spring]
stiffness = 320.0
damping = 36.0
mass = 1.0

[tiling]
inner_gap = 10.0
outer_gap = 10.0
smart_gaps = true
default_split = "automatic"

[input]
focus_follows_mouse = false
xkb_layout = "us"
xkb_variant = ""
xkb_options = []
repeat_rate = 25
repeat_delay_ms = 600

[input.touchpad]
tap = true
natural_scroll = true
disable_while_typing = true

[commands]
terminal = ["foot"]

[[bindings]]
keys = "Super+Enter"
action = "spawn"
argument = "terminal"

[[bindings]]
keys = "Super+Q"
action = "close"

[[bindings]]
keys = "Super+Tab"
action = "show-overview"

[[bindings]]
keys = "Super+H"
match = "keysym"
action = "focus"
argument = "left"

[[bindings]]
keys = "Super+Space"
action = "show-launcher"

# Example: remove a built-in binding.
[[bindings]]
keys = "Super+Q"
disabled = true

[[window_rules]]
app_id = "org.example.DialogApp"
floating = true
```

Command values are argument arrays, never shell command strings. Binding records
use a normalized key chord, match mode, action, and optional argument. `keysym`
matching is the default and follows the active XKB layout. `physical` matching
uses XKB physical key names and is independent of the selected layout.

The complete built-in set is listed in Section 14; when a user supplies a record
for the same chord and match mode it replaces that default. A record with
`disabled = true` and no action explicitly unbinds the matching default.

Duplicate normalized bindings, unknown actions, invalid arguments, and
references to missing commands MUST fail validation. Every built-in binding
MUST be expressible, replaceable, and removable through this schema.

`ferese-config` MUST assemble all enabled namespace schemas and validate the
entire candidate configuration before applying any part of it. No companion
component may maintain an independent competing copy of visual or shell
configuration.

The launcher and overview actions are desktop-tier defaults and MUST be installed
only when their shell features are available. Their absence from a v0-only
installation is not a validation error.

Unknown fields SHOULD warn. Invalid types and invalid domain values MUST fail the
owning schema's validation.

Reload MUST debounce duplicate events, read the entire file, parse, validate,
construct, and apply the difference as one transaction. Invalid input MUST NOT
replace active configuration. Errors MUST be logged and emitted through IPC.

Settings and IPC MUST use the same validation path. Persistent changes MUST be
written atomically using a temporary file and rename.

## 13. IPC and security

### 13.1 Transport and trust

The user-control socket is `$XDG_RUNTIME_DIR/ferese/control.sock`. Its parent
directory MUST be owned by the user with mode `0700`; the socket MUST use `0600`.
The compositor MUST reject peers whose effective UID, read from OS peer
credentials, differs from its own.

Same-UID checks authorize user control only; they do not identify a trusted UI
client. Privileged Wayland access is capability-scoped per client. Initial
capabilities are:

```text
effects
shell-control
capture
virtual-input
```

Trusted UI processes MUST receive a private Wayland connection created by the
compositor. Ferese creates a socket pair, registers the server end as a Wayland
client, and passes the client end only through an inherited descriptor such as
`WAYLAND_SOCKET`. Privilege MUST NOT depend on PID, executable name, command-line
arguments, environment secrets, or a discoverable private socket path.

The compositor associates an explicit capability set with each private Wayland
client and filters private globals and requests against that set.

`ferese-effects-v1` requires `effects`. `ferese-shell-v1` requires
`shell-control`. `ferese-shell` receives only the capabilities required by
enabled shell features. `ferese-settings` MAY receive `effects` when spawned as
a trusted Ferese component; its configuration changes still use the normal
validated configuration/IPC path.

Public layer-shell does not require a private capability. The private `capture`
capability permits unattended capture only for a trusted component. Public
screencopy clients remain subject to interactive or configured capture policy
and do not acquire `capture` merely by binding a public global.

If a trusted component launches another privileged Ferese component, it MUST ask
the compositor to create and pass a new capability-scoped private connection;
it MUST NOT forward its own Wayland descriptor or capabilities.

Ferese does not ship a polkit authentication agent in the initial desktop tier.
Security-sensitive actions requiring system authentication MUST use an external
agent until a separate authentication-agent security specification exists.

### 13.2 Framing

IPC v0 uses unsigned 32-bit big-endian length-prefixed UTF-8 JSON:

```text
4-byte payload length | JSON payload bytes
```

The maximum payload is 1 MiB. Oversized, truncated, invalid UTF-8, or invalid
JSON frames close the connection after a rate-limited diagnostic.

```json
{
  "version": 1,
  "id": 42,
  "type": "command",
  "command": "focus",
  "args": { "direction": "left" }
}
```

Responses echo `id` and contain exactly one of `result` or `error`:

```json
{
  "version": 1,
  "id": 42,
  "result": {}
}
```

Errors have stable codes. Unknown fields MAY be ignored; unknown commands and
unsupported versions MUST return errors.

### 13.3 Commands and events

User-control commands are:

```text
focus                 move
resize                workspace
move-to-workspace     toggle-floating
toggle-fullscreen     close
reload-config         get-focused-window
get-workspaces        get-outputs
get-config            set-config
show-overview         hide-overview
show-launcher         hide-launcher
```

Managed-window enumeration, application identity metadata, shell activation,
close, and overview-selection operations used by `ferese-shell` belong to the
private `ferese-shell-v1` protocol rather than widening normal user-control IPC.

Events include `window-opened`, `window-closed`, `window-focused`,
`window-moved`, `workspace-changed`, `output-added`, `output-removed`,
`config-changed`, and `config-error`.

Subscribers have bounded queues. The server MUST disconnect a subscriber whose
queue overflows rather than block the compositor.

## 14. Input

Ferese MUST support click-to-focus, configurable focus-follows-pointer, floating
move/resize, tiled rearrangement and divider resizing, pointer constraints,
relative pointer, cursor-shape, text input, configurable XKB layout and repeat,
touchpad tap/natural-scroll policy, and configurable bindings. Default bindings
match keysyms, so `Super+H/J/K/L` follows the active keyboard layout. Users MAY
select physical matching per binding when spatial key positions are desired.

A focused client MAY inhibit compositor shortcuts only while its requesting
surface is visible and holds keyboard focus. Ferese MUST retain an emergency
escape binding that cannot be inhibited. Input-method activation MUST follow the
focused text-input request and MUST NOT grant the input-method client general
shortcut or capture authority.

```text
Super+Enter             terminal
Super+Q                 close window
Super+H/J/K/L           focus left/down/up/right
Super+Shift+H/J/K/L     move left/down/up/right
Super+1..9              switch workspace
Super+Shift+1..9        move window to workspace
Super+F                 toggle fullscreen
Super+Shift+Space       toggle floating
Super+Space             launcher
Super+Tab               overview
```

The launcher and overview bindings are desktop-tier defaults and MUST be
installed only when their actions are available. Their absence from a v0-only
installation is not a binding error.

Bare `Super` MUST NOT activate overview. Interactive grabs MUST have explicit
cancellation. Losing a device, seat, surface, or output during a grab MUST end it
safely.

## 15. Outputs

Each connected output has a mode, scale, transform, logical position, usable
region, and one active workspace. v0 MAY choose preferred modes automatically
but MUST handle hotplug without losing windows.

On startup, the first output creates and activates workspace `1`. Selecting an
uncreated numeric workspace from `1` through `9` creates it on the focused
output. A newly connected output receives the lowest unused numeric workspace
name and activates it; this MUST NOT silently move an existing workspace.

Output removal selects a target from the remaining outputs in this order:

1. the v0 seat's focused output, if it remains connected;
2. nearest output to the removed output by logical-center distance;
3. lowest stable `OutputId` as a tie-breaker.

A workspace MAY move between outputs but MUST NOT appear on two outputs at once.
Switching to a workspace already visible on another output changes the seat's
focused output/workspace to that existing presentation and MUST NOT implicitly
move or swap workspaces.

When an output is removed, the migration target keeps its current active
workspace unless the removed output held the seat focus. In that case, the
removed output's active workspace becomes active on the target and the seat's
managed-window focus is restored there where possible.

Ferese MUST derive a persistent output identity from stable connector and EDID
properties and record the workspaces evacuated during the compositor lifetime.
When that output returns, those workspaces return to it atomically if they still
reside on their automatic migration target and have not been explicitly moved
since disconnection. Its previous active workspace is restored when available.
Explicit user movement wins; Ferese MUST NOT take a workspace back from a new
assignment. If no recorded workspace can return, normal new-output assignment
applies.

## 16. Performance and observability

The target is sustained output refresh at 60 Hz on integrated graphics during
ordinary use. Animation MUST also work at higher and variable refresh rates.

Ferese SHOULD track frame, render, layout and blur duration; damaged pixels;
missed presentation deadlines; surface, semantic-material, and blur-region counts; and active
animations. Performance tracing MUST be optional. Suggested targets are
`ferese::wayland`, `ferese::layout`, `ferese::render`, `ferese::input`,
`ferese::ipc`, and `ferese::xwayland`.

## 17. Testing

### 17.1 Layout

Unit tests MUST cover insertion, deletion, focus, movement, ratios, constraints,
resize, stacks, floating transitions, fullscreen placement preservation,
workspace migration and restoration, gaps, shared-edge rounding, and
deterministic geometry. They MUST NOT require Wayland. Property tests SHOULD
prove arbitrary operation sequences preserve acyclic trees, valid parentage and
stack cardinality, and do not duplicate or lose windows.

### 17.2 Configuration

Tests MUST cover defaults, partial files, unknown fields, invalid and non-finite
values, duplicate key chords, unknown binding actions, missing command
references, keysym versus physical matching, default unbinding, window-rule
ordering, theme/shell namespace ownership, reload rollback, serialization, and atomic updates.

### 17.3 IPC and security

Tests MUST cover partial reads, multiple frames per read, oversized frames,
unsupported versions, subscriptions, slow clients, peer-UID rejection, and
denial of privileged commands without capability, `shell-control` filtering, and
public layer-shell remaining unprivileged. Launch tests MUST prove that
children receive the public display and activation token but cannot inherit any
private Wayland or privileged IPC descriptor.

### 17.4 Rendering and integration

Pure tests MUST cover clipping, shadow bounds, damage expansion, blur sampling,
cache invalidation, transforms, animated hit testing, and refresh-rate-independent
interpolation. Geometry tests MUST cover mismatches between logical target,
visual geometry, configured client size, and committed client size. Nested
integration tests SHOULD cover configure/commit behavior, inverse-transformed
input during animation, clipboard, popups, drag-and-drop, focus, fullscreen,
xdg-activation, output removal, private-client capability filtering, overview
scene transitions, top-bar reservation restart grace, application-identity association,
DND behavior, notification replacement/actions, and shell restart.

## 18. Milestones

A milestone is complete only when its acceptance criteria pass. M0 through M6
form the v0 release path. M7 through M10 are independently gated desktop-tier
work and MUST NOT delay the v0 release.

### M0: Native window on screen

Implement the nested backend, public Wayland socket, output, seat, xdg-shell,
basic renderer, and commit handling.

Acceptance: `foot` opens and redraws; keyboard, pointer, and popups work; closing
a client leaves the compositor running.

### M1: Essential native protocols

Implement clipboard, primary selection, drag-and-drop, decoration negotiation,
xdg-activation, relative pointer, pointer constraints, presentation timing, and
scaling.

Acceptance: text copies between native clients; drag-and-drop completes;
decorated and undecorated clients can move and resize; scaled hit testing matches
rendered content; a user-initiated test launch receives a valid activation token.

### M2: Tiling and workspaces

Implement identifiers, layout trees, insertion, focus, movement, resize, gaps,
floating, fullscreen, and workspaces.

Acceptance: five terminals tile without overlap; navigation works in all
directions; close reflows layout; modes restore correctly; randomized tests
preserve all invariants.

### M3: Animated geometry

Implement logical, visual, and client geometry separation plus timestamp-driven
animation.

Acceptance: layout changes do not jump; one non-interactive reflow does not send
per-frame configure events; a client may commit its final size mid-animation
without restarting the transition; inverse-transformed hit testing matches the
visible surface; input stays responsive.

### M4: Early hardware session

Implement the smallest useful libseat, DRM/KMS, GBM, libinput, and session-
lifecycle path for one output. Record page-flip presentation timestamps and
missed-deadline metrics. Keep the nested backend for development.

Acceptance: Ferese starts from a TTY, renders the M3 workload directly, survives
session deactivate/reactivate, and drives animation from measured presentation
timing. Frame pacing and animation are measured on the reference integrated GPU
before blur or shell work begins.

### M5: Native desktop interoperability

Implement layer-shell, cursor-shape, text-input/input-method, shortcut inhibit,
idle notify/inhibit, xdg-foreign, single-pixel-buffer, screencopy authorization,
multi-output hotplug, and the remaining Section 8.1 protocols.

Acceptance: representative native panels, launchers, notification daemons, IMEs,
VM/remote-desktop clients, and screenshot clients exercise their protocols;
output removal and return obey Section 15; security-sensitive requests are
denied without the required policy decision.

### M6: Shippable v0 core

Implement rounded clipping, shadows, active borders, transparency, damage
expansion, validated textual configuration, input settings, window rules,
direct application launching, IPC, and `feresectl`. Complete native-client crash,
soak, and performance testing.

Acceptance: masks and damage are correct; configuration reload is transactional;
defaults can be replaced or unbound; `feresectl` commands work reliably; a
configured terminal launches without shell parsing; malformed clients do not
affect availability; a 24-hour native-client soak has no compositor crash or
unbounded resource growth; all Section 3.1 requirements pass.

### M7: Semantic surface materials

Before choosing a shell toolkit, build a minimal `wayland-client` probe that
creates a layer-shell surface and requests `surface.panel` through
`ferese-effects-v1`. Then implement semantic role resolution for glass,
translucent, and solid styles plus backdrop capture, blur, tint, saturation,
optional noise, caching, and invalidation.

Acceptance: the probe can switch among glass, translucent, and solid without
changing geometry; glass blurs only content behind its surface; backdrop changes
invalidate correctly; the effects global is visible only to a client with the
`effects` capability; a public client cannot bind it; the demo meets its frame
budget on the reference integrated GPU.

### M8: Overview and shell

First spike GPUI layer-surface creation, output discovery, focus, configure, and
shutdown behavior. If the spike fails its lifecycle tests, use a thin native
Wayland shell adapter or record a toolkit decision before proceeding. Implement
the compositor overview scene, minimal `ferese-shell-v1` control/metadata
protocol, top bar, apps-only launcher UI, workspace UI, OSD, and the standard
notifications D-Bus service.

Acceptance: normal shell surfaces use public layer-shell; `Super+Tab` controls
overview; managed windows remain compositor-owned live scene nodes; selection
follows visual geometry; the apps-only launcher uses application identity and
XDG activation; DND and notification replacement/actions work; fullscreen hides
the top bar without changing underlying layout geometry; shell restart preserves
the top-bar reservation through its grace period; each trusted process receives
only its assigned capabilities.

### M9: Settings and portals

Build Theme/Appearance, Tiling, Shortcuts, Input, Workspaces, Displays, and About.
Implement the portal backend and PipeWire integration for screenshots and screen
sharing.

Acceptance: controls preview live; invalid changes do not replace active config;
changes survive restart; shortcut editing can replace and unbind defaults; the
Displays page represents hotplug and return behavior; portal requests require an
interactive authorization path and produce working screenshots/streams.

### M10: X11 compatibility and desktop stabilization

Integrate `xwayland-satellite` on demand and complete desktop-tier crash, soak,
compatibility, and performance testing. Replacing the satellite with an embedded
X11 window manager requires the architectural decision from Section 8.3.

Acceptance: representative X11 applications tile and float; clipboard works both
ways; menus, dialogs, games, and absolute-position requests have documented test
results; a 24-hour mixed-client soak has no compositor crash or unbounded
resource growth; all Section 3.2 desktop-tier requirements pass.

## 19. First implementation slice

```text
nested Smithay compositor
  -> two xdg-shell terminals
  -> deterministic two-window tiling
  -> logical/visual/client geometry separation
  -> spring reflow with coalesced final configure
```

The slice succeeds when A and B tile automatically; closing B immediately updates
the logical layout while A expands visually; A receives no per-frame configure
flood; pointer input remains aligned through inverse transforms; shared edges
round identically; terminal changes damage the correct regions; and all
interaction remains responsive.

M4 follows this nested slice immediately so frame pacing is validated on real
hardware. Semantic materials, GPUI, Settings, XWayland, notifications, portals, and the
graphical shell MUST NOT delay it or the v0 core.

## 20. Definition of v0

Ferese v0 is complete when a user can:

1. start a direct Ferese session;
2. run ordinary native Wayland applications and layer-shell utilities;
3. copy, paste, drag, and use application popups;
4. tile, focus, move, resize, float, fullscreen, and close windows;
5. use multiple workspaces and outputs;
6. configure input, bindings, rules, gaps, corners, borders, shadows, and
   animations through validated live reload;
7. launch configured applications directly;
8. use an IME, inhibit shortcuts where allowed, take an authorized screenshot,
   and resume after output removal or session switching;
9. control permitted behavior through `feresectl`; and
10. perform routine native-Wayland programming work without regular compositor
    restarts.

The intended v0 result is a low-latency, independently usable tiling compositor.
The desktop tier adds a coherent Ferese shell, semantic surface materials,
graphical settings,
portals, and X11 compatibility without redefining core correctness. Visual
effects support hierarchy and usability; they do not replace correctness,
responsiveness, or security.