diff --git a/docs/build.md b/docs/build.md
index 8139ab3..28e57c3 100644
--- a/docs/build.md
+++ b/docs/build.md
@@ -27,7 +27,7 @@ For automatic rebuilds, install `watchexec` or `fswatch` and run:
 just dev
 ```
 
-`just run` starts the hot-reload loader in the foreground; use `just reload` manually from another terminal after editing `src/game`. `just dev` starts the loader in the background and keeps a file watcher running in the foreground to call `just reload` automatically when `src/game` changes.
+`just run` starts the hot-reload loader in the foreground; use `just reload` manually from another terminal after editing `src/game` or `src/sim`. `just dev` starts the loader in the background and keeps a file watcher running in the foreground to call `just reload` automatically when either package changes.
 
 ## Release
 
diff --git a/docs/tickets/001-architecture.md b/docs/tickets/001-architecture.md
index 221083f..c180f68 100644
--- a/docs/tickets/001-architecture.md
+++ b/docs/tickets/001-architecture.md
@@ -10,22 +10,25 @@ The current `src/game` package is intentionally flat and almost empty. Before ad
 
 This ticket should not build gameplay. It should create the places gameplay will live.
 
-## Proposed Shape
+## Implemented Shape
 
-Keep everything in the `game` package for now. Split by responsibility, not by abstraction layer.
+Split platform-facing game code from deterministic simulation code. The `game` package owns Raylib, exported entry points, input sampling, and rendering. The `sim` package owns authoritative gameplay state, fixed-tick mutation, replay data, and world data.
 
-Suggested files:
+Current files:
 
 - `src/game/app.odin`: exported `game_*` API coordination and top-level update flow.
 - `src/game/memory.odin`: `Game_Memory` and long-lived allocations/state roots.
-- `src/game/sim.odin`: fixed-step simulation types and entry points.
-- `src/game/input.odin`: platform input sampling and normalized simulation commands.
-- `src/game/replay.odin`: run input history, replay cursors, and deterministic replay helpers.
-- `src/game/world.odin`: prototype world state, actors, rooms, and gameplay data.
+- `src/game/input.odin`: platform input sampling into normalized simulation commands.
+- `src/game/keymap.odin`: action-to-hardware binding configuration.
 - `src/game/render.odin`: rendering from simulation state.
-- `src/game/config.odin`: constants and compile-time config.
+- `src/game/config.odin`: window and app-facing compile-time config.
+- `src/sim/sim.odin`: fixed-step simulation state and entry points.
+- `src/sim/input.odin`: normalized simulation commands.
+- `src/sim/replay.odin`: run input history, replay cursors, and deterministic replay helpers.
+- `src/sim/world.odin`: prototype world state, actors, rooms, and gameplay data.
+- `src/sim/config.odin`: simulation constants and replay-affecting config.
 
-Exact names can change if implementation reveals a better split, but the ownership boundaries should remain clear.
+The main boundary is that `src/sim` should stay free of Raylib, rendering, frame-time, and platform APIs so replay behavior can be tested without opening a window.
 
 ## Requirements
 
@@ -39,7 +42,7 @@ Exact names can change if implementation reveals a better split, but the ownersh
 
 ## Acceptance Criteria
 
-- `src/game` has a clear file structure for app lifecycle, simulation, input, replay, world, and rendering.
+- `src/game` and `src/sim` have a clear file structure for app lifecycle, simulation, input, replay, world, and rendering.
 - `game_update` delegates to explicit update/render functions instead of owning all behavior inline.
 - `Game_Memory` is the only persistent root needed by the hot-reload API.
 - No gameplay behavior is implemented beyond what is necessary to keep the app running.
diff --git a/justfile b/justfile
index a28a0c5..cda9171 100644
--- a/justfile
+++ b/justfile
@@ -54,10 +54,10 @@ reload: build-game
 dev: build-game build-loader
     @if command -v watchexec >/dev/null 2>&1; then \
         ./{{ hot_exe }} & \
-        watchexec -w {{ game_pkg }} -e odin -- just reload; \
+        watchexec -w {{ game_pkg }} -w {{ sim_pkg }} -e odin -- just reload; \
     elif command -v fswatch >/dev/null 2>&1; then \
         ./{{ hot_exe }} & \
-        fswatch -o {{ game_pkg }} | while read -r _event; do just reload; done; \
+        fswatch -o {{ game_pkg }} {{ sim_pkg }} | while read -r _event; do just reload; done; \
     else \
         printf "watchexec or fswatch is required for 'just dev'. Install one or use 'just run' + 'just reload'.\n"; \
         exit 1; \