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+# Downstroke Demo Games Design
+
+**Date:** 2026-04-05
+**Status:** Approved
+**Scope:** `demo/` folder, 5 demo games, Makefile `make demos` target, CLAUDE.md update
+
+---
+
+## Goal
+
+Provide 5 small self-contained demo games in `demo/` that collectively exercise every engine system. Each demo compiles to its own executable (`bin/demo-*`). They replace the macroknight integration test for Milestone 8 and serve as living documentation of the engine API.
+
+---
+
+## File Layout
+
+```
+demo/
+  assets/                        ← copied from macroknight/assets (not symlinked)
+    monochrome-transparent.png   ← tileset spritesheet
+    monochrome_transparent.tsx   ← tileset metadata (TSX)
+    level-0.tmx                  ← level used by platformer, topdown, sandbox
+    DejaVuSans.ttf               ← font for audio demo text
+    jump.wav                     ← sound effect (platformer jump, shmup shoot)
+    theme.ogg                    ← music (audio demo)
+  platformer.scm
+  shmup.scm
+  topdown.scm
+  audio.scm
+  sandbox.scm
+```
+
+**Omitted from copy:** `prefabs.scm`, `macroknight.tiled-project`, `macroknight.tiled-session` — macroknight-specific files not needed by any demo.
+
+**Audio modules:** `mixer.scm` and `sound.scm` are copied from `macroknight/` into the downstroke repo root and added to the build. They are engine-level modules and are required by any demo that uses audio.
+
+When copying `sound.scm`, add one function that macroknight's version omits:
+```scheme
+(define (stop-music!) (mix-halt-music))
+```
+The audio demo uses `stop-music!` to toggle music off.
+
+---
+
+## Build
+
+### Makefile additions
+
+```makefile
+DEMO_NAMES := platformer shmup topdown audio sandbox
+DEMO_BINS  := $(patsubst %,bin/demo-%,$(DEMO_NAMES))
+
+demos: engine $(DEMO_BINS)
+
+bin/demo-%: demo/%.scm $(OBJECT_FILES) | bin
+	csc demo/$*.scm $(OBJECT_FILES) -o bin/demo-$* -I bin
+```
+
+- `make` — builds engine modules only (unchanged)
+- `make demos` — builds all 5 demo executables; depends on engine being built first
+- Demos are compiled as programs (not units), linked against all engine `.o` files
+- `$(OBJECT_FILES)` includes `mixer` and `sound` once those modules are added to `MODULE_NAMES`
+
+### `render-scene!` nil guards
+
+`render-scene!` in `renderer.scm` is updated so that entity drawing is **nested inside** the tilemap guard:
+
+- Tilemap drawing only fires if `(scene-tilemap scene)` is not `#f`
+- Entity drawing only fires if **both** `(scene-tilemap scene)` AND `(scene-tileset-texture scene)` are not `#f`
+
+```scheme
+(when tilemap
+  (draw-tilemap renderer camera tileset-texture tilemap)
+  (when tileset-texture
+    (let ((tileset (tilemap-tileset tilemap)))
+      (draw-entities renderer camera tileset tileset-texture entities))))
+```
+
+**Consequence for shmup:** since shmup has no tilemap, the engine will not draw its entities. Shmup draws its player, bullets, and enemies as **colored SDL rectangles** in its `render:` hook — matching the original "colored rects" intent. This is acceptable because shmup entities are simple geometric shapes, not sprites.
+
+Audio (no scene at all) works because `engine.scm` guards `render-scene!` with `(when (game-scene game) ...)`.
+
+### CLAUDE.md update
+
+Add to the Build & Test section:
+
+> `make demos` must always succeed. A demo that fails to compile is a build failure. Run `make && make demos` to verify both engine and demos build cleanly.
+
+---
+
+## Demo Code Pattern
+
+Every demo follows this ~30-line structure:
+
+```scheme
+(import (prefix sdl2 "sdl2:")
+        (prefix sdl2-ttf "ttf:")
+        (prefix sdl2-image "img:")
+        downstroke/engine
+        downstroke/world
+        downstroke/tilemap
+        downstroke/renderer
+        downstroke/input
+        downstroke/physics
+        downstroke/assets)
+
+(define *game*
+  (make-game
+    title: "Demo: <Name>" width: 600 height: 400
+    preload: (lambda (game) ...)   ;; load tilemap, tileset texture, sounds
+    create:  (lambda (game) ...)   ;; build scene, place entities
+    update:  (lambda (game dt) ...)  ;; input dispatch, physics calls
+    render:  (lambda (game) ...)))   ;; HUD overlay (optional)
+
+(game-run! *game*)
+```
+
+Tile IDs in entity plists are placeholder values — to be adjusted visually after first run.
+
+---
+
+## The 5 Demos
+
+### 1. `demo/platformer.scm` — Platformer
+
+**Systems exercised:** `input`, `physics` (gravity + tile collision), `renderer` (tilemap + entities), `world`/scene, camera follow, audio (sound effect)
+
+**Mechanics:**
+- Player entity with gravity, left/right movement, jump
+- Tile collision via `apply-physics` from `physics.scm`
+- Camera follows player horizontally
+- Jump sound via `(play-sound 'jump)` (loaded in preload: as `'(jump . "demo/assets/jump.wav")`)
+- Level: `demo/assets/level-0.tmx`
+- Tile IDs: placeholder (user adjusts)
+
+**Key entity plist:**
+```scheme
+(list #:type 'player
+      #:x 100 #:y 50
+      #:width 16 #:height 16
+      #:vx 0 #:vy 0
+      #:gravity? #t
+      #:on-ground? #f
+      #:tile-id 1)
+```
+
+**Update logic:** read input → set `#:vx` from left/right → jump sets `#:vy` → call physics step → update camera x to follow player x.
+
+---
+
+### 2. `demo/shmup.scm` — Shoot-em-up
+
+**Systems exercised:** `entity` (spawning/removal), manual AABB entity-entity collision (removal-based, not `physics.scm`), `input`, `renderer` (SDL colored rects), `world`/scene (no tilemap)
+
+**Mechanics:**
+- Player ship at bottom, moves left/right
+- Space bar fires bullet upward (new entity added to scene)
+- Enemies spawn from top at random x positions every N frames, move downward
+- Bullet-enemy collision: both entities removed from scene
+- No tilemap — plain background (black/SDL clear)
+- No gravity on any entity
+- `jump.wav` plays on shoot
+
+**Key entity plists:** (no `#:tile-id` — entities are drawn as colored rects)
+```scheme
+;; player
+(list #:type 'player #:x 280 #:y 360 #:width 16 #:height 16 #:vx 0 #:vy 0)
+;; bullet
+(list #:type 'bullet #:x px #:y 340 #:width 4 #:height 8 #:vx 0 #:vy -5)
+;; enemy
+(list #:type 'enemy  #:x rx #:y 0   #:width 16 #:height 16 #:vx 0 #:vy 2)
+```
+
+**Rendering:** shmup has no tilemap, so `render-scene!` draws nothing for this scene. Shmup implements its own `render:` hook using `sdl2:render-fill-rect!` with distinct colors (player = white, bullet = yellow, enemy = red). The camera is at (0,0) so screen coords == world coords.
+
+**Update logic:** move entities by vx/vy each frame → manual AABB collision check between bullets and enemies (not `resolve-entity-collisions` — shmup uses removal, not push-apart) → filter removed entities from scene → spawn new enemy every 60 frames → read input for player movement and shoot.
+
+---
+
+### 3. `demo/topdown.scm` — Top-down explorer
+
+**Systems exercised:** `input` (8-directional), `renderer` (tilemap + entity), `world`/scene, camera follow (both axes), `physics` (no gravity)
+
+**Mechanics:**
+- Player entity moves in 8 directions (WASD or arrows)
+- No gravity (`#:gravity? #f`)
+- Camera follows player on both x and y axes
+- Level: `demo/assets/level-0.tmx` (same tilemap, different movement feel)
+- Tileset texture loaded in preload: — required for entity sprite rendering (tilemap + tileset-texture both present so render-scene! draws entities via tileset)
+- No audio
+
+**Update logic:** read input → set `#:vx` and `#:vy` from direction keys → apply tile collision (no gravity component) → update camera to center on player.
+
+---
+
+### 4. `demo/audio.scm` — Audio showcase
+
+**Systems exercised:** audio (sound effects + music), `renderer` (text via `draw-ui-text`), `input`, `assets`
+
+**Mechanics:**
+- Static screen with text instructions rendered via `draw-ui-text`
+- Press **J** → play `jump.wav`
+- Press **M** → toggle `theme.ogg` music on/off
+- Press **Escape** → quit
+- No tilemap, no physics, no moving entities
+- Uses `DejaVuSans.ttf` for text
+- Audio calls via `sound.scm` functions: `load-sounds!`, `play-sound`, `load-music!`, `play-music!`, `stop-music!` (added when copying sound.scm — see File Layout)
+
+**Display:** colored rectangle background + text labels for each key binding.
+
+---
+
+### 5. `demo/sandbox.scm` — Physics sandbox
+
+**Systems exercised:** `physics` (gravity + tile collision + entity-entity collision), `renderer`, `world`/scene, no player input
+
+**Mechanics:**
+- 10 entities spawned at random x positions near the top of the screen
+- All have `#:gravity? #t` and `#:solid? #t` (required for `resolve-entity-collisions` to participate)
+- Physics step runs each frame (gravity accelerates, tile collision stops them)
+- Entities rest on floor tiles or bounce (depending on physics.scm behavior)
+- No player — pure observation of physics pipeline
+- Level: `demo/assets/level-0.tmx`
+- After all entities settle (or after 10 seconds), loop: despawn all, respawn at new random positions
+
+---
+
+## Systems Coverage Matrix
+
+| System / Module | platformer | shmup | topdown | audio | sandbox |
+|---|---|---|---|---|---|
+| `engine` (make-game, game-run!) | ✓ | ✓ | ✓ | ✓ | ✓ |
+| `input` | ✓ | ✓ | ✓ | ✓ | — |
+| `physics` (gravity) | ✓ | — | — | — | ✓ |
+| `physics` (tile collision) | ✓ | — | ✓ | — | ✓ |
+| `physics` (entity collision) | — | — | — | — | ✓ |
+| manual AABB (removal) | — | ✓ | — | — | — |
+| `renderer` (tilemap) | ✓ | — | ✓ | — | ✓ |
+| `renderer` (entities) | ✓ | — | ✓ | — | ✓ |
+| `renderer` (SDL colored rects) | — | ✓ | — | — | — |
+| `renderer` (text) | — | — | — | ✓ | — |
+| `world` / scene | ✓ | ✓ | ✓ | — | ✓ |
+| `assets` registry | ✓ | ✓ | ✓ | ✓ | ✓ |
+| audio (sound) | ✓ | ✓ | — | ✓ | — |
+| audio (music) | — | — | — | ✓ | — |
+| camera follow | ✓ (x) | — | ✓ (xy) | — | — |
+
+---
+
+## Out of Scope
+
+- Animation state machine (`animation.scm`) — not yet extracted to downstroke
+- AI (`ai.scm`) — not yet extracted
+- Prefab system — not yet extracted
+- Scene transitions — Milestone 9
+- Asset-type-specific load helpers (`game-load-tilemap!` etc.) — Milestone 6
diff --git a/docs/superpowers/specs/2026-04-05-milestone-8-game-object-lifecycle-design.md b/docs/superpowers/specs/2026-04-05-milestone-8-game-object-lifecycle-design.md
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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