Document that package.json aliases may target only direct subfolders of src

AGENTS.md

@@ -19,6 +19,11 @@ dependency. Keep the sources to erasable syntax and `.ts` imports, which
 type-checks, and `vp test` runs Vitest. Unit tests sit next to the code as
 `src/*.test.ts`; repository-level tests live in `tests/`.
 
+`src/` is flat, so `package.json` has no `imports` aliases and modules, tests,
+and `scripts/` import each other relatively. If one is ever added, it may point
+only at a direct subfolder of `src/` (its `index.ts`, or a `#x/*` pattern
+inside it); never at `src/` itself, a deeper folder, or anything outside `src/`.
+
 The only config files are `package.json`, `tsconfig.json`, and
 `vite.config.ts`, plus `package-lock.json`. Repo-local lint rules and the rule
 list live in `scripts/project-lint.ts`. Lint disable comments are not allowed;