diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..5c8681d
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,51 @@
+# Architecture Rules
+
+Follow these rules for the whole repository. More specific `AGENTS.md` files override/add rules for their folders.
+
+## Boundaries
+- `core/`: pure domain models only. See `core/AGENTS.md`.
+- `commands/`: the only write path for application state.
+- `editor/`: transient editor/app state types, e.g. viewport/camera and selection.
+- `renderer/`: renders the current `ImageDocument` using the graphics backend, e.g. WebGL.
+- `view/`: React UI shell and controls only.
+
+## State Ownership
+- All persistent document state is represented by `ImageDocument` and related `core/` models.
+- Transient editor state is application state too: viewport/camera, selection, tools, active artboard/layer, drag state, etc.
+- Commands are the only code allowed to create, replace, or mutate persistent or transient state.
+- React must not own, manage, derive authoritative, or alter document/editor state.
+- React may hold only local ephemeral UI details with no app meaning, e.g. open popover, hovered button, uncontrolled input draft before command submit.
+- Do not update state directly from React event handlers, renderer callbacks, effects, stores, services, or keybind handlers. Dispatch a command instead.
+
+## Commands
+- Every state change must be modeled as a command with an explicit id, payload, and context.
+- Commands must be deterministic and testable; avoid DOM, React, WebGL, timers, network, and filesystem access inside command execution.
+- Commands return/apply the next state; they should preserve domain invariants and validate payloads before changing state.
+- UI actions, menus, toolbar buttons, keybinds, and renderer interactions all request changes by dispatching commands.
+
+## React / View
+- React displays current state and exposes user intent.
+- React components receive state snapshots/selectors and command dispatch functions; they do not contain business rules.
+- Do not put rendering engine logic, document mutation logic, or editor workflow ownership in React components.
+- Effects are for UI integration/subscription setup only, not for deriving or correcting application state.
+
+## Renderer
+- The renderer draws the current `ImageDocument` plus read-only editor state overlays.
+- Renderer code must not mutate document/editor state directly.
+- Renderer interactions may emit intents/events that are translated into commands.
+- Keep rendering backend details isolated behind renderer APIs; do not leak WebGL objects into `core/`, `commands/`, or React state.
+
+## Keybinds
+- Keybind handling is ordered and explicit.
+- First check the global keybind consumer/map.
+- If the global consumer handles the keybind, stop.
+- If not consumed globally, the keybind may be consumed by dispatching a command.
+- Keybind handlers must not mutate state directly.
+- Avoid ad-hoc component-local shortcuts unless they are purely local UI behavior and cannot affect app/editor/document state.
+
+## Imports
+- `core/` imports nothing from app layers.
+- `commands/` may import `core/` and `editor/`; avoid importing React or renderer backend APIs.
+- `editor/` may import `core/` types; it must not import React, commands, renderer, storage, or backend APIs.
+- `renderer/` may import `core/` and `editor/` types; it must not import React components.
+- `view/` may import UI components and command dispatch interfaces; avoid importing renderer internals except through stable view-facing adapters.
diff --git a/commands/command.ts b/commands/command.ts
index a855412..ffc9bf3 100644
--- a/commands/command.ts
+++ b/commands/command.ts
@@ -1,11 +1,11 @@
-import type { ImageDocument } from "@core/document";
+import type { AppState } from "@editor/state";
 
 export type CommandContext = {
-  document: ImageDocument;
+  state: AppState;
 };
 
 export type Command<TPayload = void> = {
   id: string;
   name: string;
-  execute(context: CommandContext, payload: TPayload): ImageDocument;
+  execute(context: CommandContext, payload: TPayload): AppState;
 };
diff --git a/core/AGENTS.md b/core/AGENTS.md
new file mode 100644
index 0000000..cf7ee0d
--- /dev/null
+++ b/core/AGENTS.md
@@ -0,0 +1,34 @@
+# Core Domain Model Rules
+
+Follow these rules for all changes in `core/`.
+
+## Purpose
+- `core/` contains pure domain types for the image editor: documents, artboards, layers, assets, ids, and geometry.
+- Keep it framework-free, runtime-light, and reusable by renderer, commands, persistence, and tests.
+
+## Hard Rules
+- Do not import React, DOM APIs, UI components, storage, networking, filesystem, command handlers, or renderer code.
+- Do not add side effects, global state, caches, singletons, or environment-dependent behavior.
+- Prefer exported TypeScript `type`s. Add runtime code only when it is pure, deterministic, and domain-generic.
+- Keep domain files small and focused. One concept per file; re-export public types from `core/index.ts`.
+- Use `import type` / `export type` for type-only dependencies.
+- Preserve discriminated unions. Every `Layer` variant must have a stable `type` string.
+- Do not weaken domain types with `any`, broad `string | number` unions, optional fields, or nullable values unless the domain truly allows absence.
+- IDs are opaque aliases from `id.ts`; do not inline plain `string` ID fields in models.
+- Do not duplicate geometry shapes outside `geometry.ts`. Use `Vec2D`, `Size`, `Rect`, `Bounds`, `Transform`, `Mat2D`, and `CoordinateSpace`.
+- Avoid app/workflow concerns in names and fields. Domain models describe image-editing state, not UI state.
+
+## Model Invariants
+- `ImageDocument` owns `artboards` and shared `assets`.
+- `Artboard` owns top-level `layers` and has document-space `bounds`.
+- `LayerGroup.children` owns nested layers; only groups have children.
+- `ImageLayer.assetId` must reference an `Asset.id` in the same document.
+- `BaseLayer.opacity` is normalized `0..1`; `visible` and `locked` are explicit booleans.
+- `Transform` stores position, scale, and rotation only; derived matrices/bounds should not be persisted on models.
+- `clippingMask.maskLayerId` references another layer by `LayerId`; do not embed mask layer objects.
+
+## Changing Models
+- Before adding a field, decide whether it is core persisted state or derived/UI state. Derived/UI state does not belong here.
+- When adding a new domain type, create a focused file and export it from `index.ts`.
+- When adding a new layer kind, update the union in `layer.ts`, add a discriminant, and document its required relationships.
+- Keep names stable and serialization-friendly; assume these types may be saved, loaded, diffed, and migrated.
diff --git a/editor/index.ts b/editor/index.ts
new file mode 100644
index 0000000..7b77577
--- /dev/null
+++ b/editor/index.ts
@@ -0,0 +1 @@
+export type { AppState, EditorState, SelectionState, ViewportState } from "./state";
diff --git a/editor/state.ts b/editor/state.ts
new file mode 100644
index 0000000..f881bc8
--- /dev/null
+++ b/editor/state.ts
@@ -0,0 +1,25 @@
+import type { ImageDocument } from "@core/document";
+import type { Angle, Size, Vec2D } from "@core/geometry";
+import type { ArtboardId, LayerId } from "@core/id";
+
+export type ViewportState = {
+  center: Vec2D;
+  zoom: number;
+  rotation: Angle;
+  size: Size;
+};
+
+export type SelectionState = {
+  artboardId?: ArtboardId;
+  layerIds: LayerId[];
+};
+
+export type EditorState = {
+  viewport: ViewportState;
+  selection: SelectionState;
+};
+
+export type AppState = {
+  document: ImageDocument;
+  editor: EditorState;
+};
diff --git a/tsconfig.json b/tsconfig.json
index 7c34690..6088890 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -27,7 +27,8 @@
       "@view/*": ["./view/*"],
       "@core/*": ["./core/*"],
       "@renderer/*": ["./renderer/*"],
-      "@commands/*": ["./commands/*"]
+      "@commands/*": ["./commands/*"],
+      "@editor/*": ["./editor/*"]
     },
 
     // Some stricter flags (disabled by default)