docs(guidelines): Define Structural Dependency Mapping (SDM) convention

conductor/code_styleguides/python.md

@@ -65,6 +65,22 @@ is processed by AI agents, while preserving readability for human review.
 - Hard limit: None — let the formatter handle wrapping if needed.
 - Rationale: 80-char limits cause excessive line continuations that waste tokens.
 
-## 10. Main Guard
+## 11. Structural Dependency Mapping (SDM)
 
-- All executable files should have `if __name__ == "__main__":` calling `main()`.
+To assist AI agents in evaluating refactoring impact across dynamic codebases, all major definitions SHOULD include terse SDM tags at the end of their docstrings.
+
+- **Format:** Tags are enclosed in square brackets at the end of the docstring body.
+- **For Functions/Methods:** `[C: CallerA, CallerB]` — List of primary internal callers within the codebase.
+- **For State Variables:**
+  - `[M: File:Line, Method]` — List of primary mutation points (where the value is assigned).
+  - `[U: File]` — Major codepaths of use (where the value is read but not changed).
+
+### Example:
+```python
+def start_services(self) -> None:
+ """
+ Initialises background threads and MCP servers.
+ [C: App.run, _cb_load_project]
+ """
+ ...
+```