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+# Milestone 8 — The Game Object and Lifecycle API
+
+**Date:** 2026-04-05
+**Status:** Approved
+**Scope:** `engine.scm`, `assets.scm`, macroknight port
+**Milestone numbering:** Follows `downstroke.org` / `TODO-engine.org` (Milestone 8). CLAUDE.md refers to the same work as "Milestone 7".
+
+---
+
+## Goal
+
+Introduce `make-game` and `game-run!` as the public entry point for downstroke. A minimal game becomes ~20 lines of Scheme. This is the "Phaser moment" — the API stabilises around a game struct with lifecycle hooks.
+
+---
+
+## Architecture
+
+Two new files:
+
+- **`engine.scm`** — `make-game` struct, `game-run!`, the frame loop, and all public accessors.
+- **`assets.scm`** — minimal key→value asset registry. No asset-type-specific logic; that is Milestone 6's domain.
+
+`engine.scm` imports: `renderer.scm`, `input.scm`, `world.scm`, `assets.scm`, the sdl2 egg (prefix `sdl2:`), `sdl2-ttf` (prefix `ttf:`), and `sdl2-image` (prefix `img:`).
+
+**Audio / mixer is not initialised by the engine in this milestone.** `mixer.scm` and `sound.scm` remain in macroknight and are not yet extracted. macroknight's `preload:` hook calls `init-audio!` directly from `sound.scm` until those modules are extracted.
+
+`physics.scm` is **not** imported by the engine. Physics is a library; the user requires it if needed and calls physics functions from their `update:` hook.
+
+### New function in `renderer.scm`
+
+`render-scene!` does not yet exist. It must be added to `renderer.scm` as part of this milestone. The module uses `export *` so no explicit export update is needed.
+
+Existing signatures in `renderer.scm` that `render-scene!` calls:
+- `(draw-tilemap renderer camera tileset-texture tilemap)` — 4 args
+- `(draw-entities renderer camera tileset tileset-texture entities)` — 5 args
+- `tilemap-tileset` is a field accessor on the `tilemap` struct (defined in `tilemap.scm`)
+
+```scheme
+(define (render-scene! renderer scene)
+  (let ((camera          (scene-camera scene))
+        (tilemap         (scene-tilemap scene))
+        (tileset-texture (scene-tileset-texture scene))
+        (tileset         (tilemap-tileset (scene-tilemap scene)))
+        (entities        (scene-entities scene)))
+    (draw-tilemap renderer camera tileset-texture tilemap)
+    (draw-entities renderer camera tileset tileset-texture entities)))
+```
+
+### Build order (Makefile)
+
+Only modules that currently exist in downstroke are listed. Modules still in macroknight (`animation`, `ai`, `prefabs`, `mixer`, `sound`) are not prerequisites for this milestone.
+
+```
+entity → tilemap → world → input → renderer → assets → engine
+```
+
+`physics` is not a link dependency of `engine` and is omitted from this chain. It is a separate build target.
+
+---
+
+## Data Structures
+
+### `game` struct (`engine.scm`)
+
+`defstruct` is called with `constructor: make-game*` so the generated raw constructor does not collide with the public keyword constructor `make-game`.
+
+```scheme
+(defstruct (game constructor: make-game*)
+  title width height
+  window renderer
+  input                ;; input-state record (accessor: game-input)
+  input-config         ;; input-config record (accessor: game-input-config)
+  assets               ;; asset registry hash table (from assets.scm)
+  frame-delay
+  preload-hook         ;; (lambda (game) ...)
+  create-hook          ;; (lambda (game) ...)
+  update-hook          ;; (lambda (game dt) ...)
+  render-hook          ;; (lambda (game) ...) — post-render overlay
+  scene)               ;; current scene struct (accessor: game-scene)
+```
+
+**Note:** There is no separate `camera` field. The camera lives inside the scene (`scene-camera`). `game-camera` is a convenience accessor (see Accessors section).
+
+### `make-game` keyword constructor
+
+```scheme
+(define (make-game #!key
+    (title "Downstroke Game")
+    (width 640) (height 480)
+    (frame-delay 16)
+    (input-config *default-input-config*)
+    (preload #f) (create #f) (update #f) (render #f))
+  (make-game*
+    title: title width: width height: height
+    window: #f renderer: #f scene: #f
+    input: (create-input-state input-config)  ;; create-input-state takes one arg: config
+    input-config: input-config
+    assets: (make-asset-registry)
+    frame-delay: frame-delay
+    preload-hook: preload
+    create-hook: create
+    update-hook: update
+    render-hook: render))
+```
+
+### Asset registry (`assets.scm`)
+
+```scheme
+(define (make-asset-registry)    (make-hash-table))
+(define (asset-set! reg key val) (hash-table-set! reg key val))
+(define (asset-ref reg key)      (hash-table-ref reg key (lambda () #f)))
+```
+
+---
+
+## Lifecycle: `game-run!`
+
+```scheme
+(define (game-run! game)
+  ;; 1. SDL2 init (no audio — mixer not yet extracted, user calls init-audio! in preload:)
+  (sdl2:init! '(video joystick game-controller))
+  (ttf:init!)
+  (img:init! '(png))
+
+  ;; 2. Create window + renderer
+  (game-window-set! game
+    (sdl2:create-window! (game-title game) 'centered 'centered
+                         (game-width game) (game-height game) '()))
+  (game-renderer-set! game
+    (sdl2:create-renderer! (game-window game) -1 '(accelerated vsync)))
+
+  ;; 3. preload hook
+  (when (game-preload-hook game) ((game-preload-hook game) game))
+
+  ;; 4. create hook
+  (when (game-create-hook game) ((game-create-hook game) game))
+
+  ;; 5. Frame loop
+  (let loop ((last-ticks (sdl2:get-ticks)))
+    (let* ((now    (sdl2:get-ticks))
+           (dt     (- now last-ticks))
+           (events (sdl2:collect-events!))
+           (input  (input-state-update (game-input game) events (game-input-config game))))
+      (game-input-set! game input)
+      (unless (input-held? input 'quit)
+        (when (game-update-hook game) ((game-update-hook game) game dt))
+        (sdl2:render-clear! (game-renderer game))
+        (when (game-scene game)
+          (render-scene! (game-renderer game) (game-scene game)))
+        (when (game-render-hook game) ((game-render-hook game) game))
+        (sdl2:render-present! (game-renderer game))
+        (sdl2:delay! (game-frame-delay game))
+        (loop now))))
+
+  ;; 6. Cleanup
+  (sdl2:destroy-window! (game-window game))
+  (sdl2:quit!))
+```
+
+**Notes:**
+- `sdl2:collect-events!` pumps the SDL2 event queue and returns a list of events (from the sdl2 egg).
+- `input-state-update` is the existing function in `input.scm`: `(input-state-update state events config)`. It is purely functional — it returns a new `input-state` record and does not mutate the existing one.
+- `create-input-state` in `input.scm` takes one argument: `(create-input-state config)` — it initialises all actions to `#f`.
+- Quit is detected via `(input-held? input 'quit)` — the `'quit` action is in `*default-input-config*` mapped to `escape` key: `(escape . quit)` in `keyboard-map`.
+- `sdl2:render-clear!` and `sdl2:render-present!` are called directly from the sdl2 egg (no wrapper needed).
+- The loop exits when `input-held?` returns true for `'quit`. No user-settable `game-running?` flag in this milestone.
+
+---
+
+## `render:` Hook Semantics
+
+Following Phaser 2.x: the engine draws the full scene first via `render-scene!` (tilemap layers + entities), then calls the user's `render:` hook. The hook is for post-render overlays only — debug info, HUD elements, custom visuals. It does not replace or suppress the engine's render pass.
+
+---
+
+## Physics
+
+Physics (`physics.scm`) is a library, not a pipeline. `game-run!` does not call any physics function automatically. Users who want physics `(require-extension downstroke/physics)` and call functions from their `update:` hook.
+
+---
+
+## Public Accessors
+
+All `game-*` readers and `game-*-set!` mutators are generated by `defstruct` and exported. Additional convenience accessors:
+
+| Accessor | Description |
+|---|---|
+| `game-renderer` | SDL2 renderer — available from `preload:` onward |
+| `game-window` | SDL2 window |
+| `game-scene` / `game-scene-set!` | Current scene struct; user sets this in `create:` |
+| `game-camera` | Convenience: `(scene-camera (game-scene game))` — derived, not a struct field. Only valid after `create:` sets a scene; calling before that is an error. |
+| `game-assets` | Full asset registry hash table |
+| `game-input` | Current `input-state` record |
+| `game-input-config` | Current `input-config` record |
+| `(game-asset game key)` | Convenience: `(asset-ref (game-assets game) key)` |
+| `(game-asset-set! game key val)` | Convenience: `(asset-set! (game-assets game) key val)` |
+
+`game-camera` is not a struct field — it is a derived accessor:
+```scheme
+(define (game-camera game)
+  (scene-camera (game-scene game)))
+```
+
+---
+
+## Scene-Level Preloading
+
+Out of scope for this milestone. A `preload:` slot will be reserved in the scene struct when `scene-loader.scm` is implemented (Milestone 7), and the two-level asset registry (global + per-scene) will be designed then.
+
+---
+
+## macroknight Port
+
+macroknight's `game.scm` must be ported to use `make-game` + `game-run!` as part of this milestone. It is the primary integration test.
+
+**What moves to the engine:** SDL2 init block (lines 87–137), the main loop (line 659+), and all frame-level rendering.
+
+**What stays in macroknight `game.scm`:** Only the three lifecycle hooks and `game-run!`:
+- `preload:` — load fonts, sounds, tilemaps (currently scattered across lines 87–137)
+- `create:` — build initial scene (currently `make-initial-game-state`, line 196)
+- `update:` — game logic, input dispatch, physics calls (currently the per-frame update functions)
+
+**Acceptance criterion:** macroknight compiles (`make` succeeds), the game runs and plays correctly (title screen → stage select → gameplay), and `game.scm` is ≤50 lines with no SDL2 init or frame-loop boilerplate.
+
+---
+
+## Out of Scope
+
+- Scene-level preloading (Milestone 7)
+- Asset-type-specific load functions (`game-load-tilemap!`, `game-load-font!`, etc.) — Milestone 6
+- `game-running?` quit flag
+- Scene state machine (Milestone 9)
+- AI tag lookup (Milestone 10)
+- Extraction of `animation`, `ai`, `prefabs`, `mixer`, `sound` modules into downstroke