sync guidelines to AGENTS v9

AGENTS.md

@@ -1,24 +1,21 @@
 # AI Agents - Project Rules
 
-**Document Version:** v8 (independent, incremented on structural changes)
+**Document Version:** v9 (independent, incremented on structural changes)
 
 Language-agnostic rules for AI assistants (Claude Code, Cursor, Copilot, etc.).
 
-Everything language-specific — package manager, formatter, linter, test framework,
+Everything specific — package manager, formatter, linter, test framework, logging library,
-logging library, line length, project layout — lives in the matching design document:
+line length, project layout, interface conventions — lives in the design documents.
 
-| Project type       | Design document                    |
+**Find them, do not look them up in a list:** every file matching `DESIGN_DOCUMENT*.md` in the
-|--------------------|------------------------------------|
+project root applies to this project. The suffix says what it covers — the language
-| Python application | `DESIGN_DOCUMENT_PYTHON.md`        |
+(`DESIGN_DOCUMENT_PYTHON.md`), whether it is an application or a library
-| Python library     | `DESIGN_DOCUMENT_PYTHON_MODULE.md` |
+(`..._PYTHON_MODULE.md`), or a part of the system that has conventions of its own
-| Rust application   | `DESIGN_DOCUMENT_RUST.md`          |
+(`..._WEBAPP.md`). A project carries as many as it needs and nothing collides, so no list here
-| Rust library       | `DESIGN_DOCUMENT_RUST_LIB.md`      |
+needs maintaining and none can go stale.
-| Godot              | `DESIGN_DOCUMENT_GODOT.md`         |
 
-The language is part of the file name, so a project that mixes languages carries one design document
+Where this file and a design document disagree, **the design document wins**. Where two design
-per language and nothing collides.
+documents disagree, the more specific one wins for what it covers.
-
-Where this file and a design document disagree, **the design document wins**.
 
 ## First-time setup