Adding more core layer stuff. Can now boot.

.agent/rules/coding-guidelines.md

@@ -22,3 +22,11 @@ Struct members: lower_snake_case. Exemple: data, node, next.
 global/static variables: lower_snake_case prefixed. Exemple: g_my_global.
 const variables: lower_snake_case prefixed. Exemple: k_my_const_var.
 Defines and Macros: ALL_CAPS_SNAKE. Exemple: MY_MACRO
+
+Modular Architecture & Include Rules:
+- Juliet uses a single-pass unity build pattern.
+- Layer aggregators `<layer>_inc.h` and `<layer>_inc.c` dictate header and source inclusion order.
+- Top-level translation units (e.g. `appbin_main.c`) include the layer `_inc` files in dependency order (`core` -> `render` -> `ui`...).
+- Sub-files within a module (e.g. `core.h`, `core_arena.c`, `render.c`) must NEVER directly `#include` other module headers, sibling headers, or configuration defines (`core_defines.h`).
+- Never add `#include` directives to sub-files to satisfy standalone LSP/compiler diagnostics. Tooling (`new_project_gen.c` / `compile_commands.json`) must supply preceding includes dynamically based on the base file include order.
+- Always explain root causes and confirm with the user before editing project architecture or files.