Coding style: Add a section about separators

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

Author: dedekind

.github/copilot-instructions.md

@@ -46,6 +46,8 @@ Compact reference for AI code generation. Human docs: [CONTRIBUTING.md](../CONTR
   its public `test_foo()`. Do not group all helpers at top and all public functions at bottom
 - [ ] Tests: use `pytest.skip("reason")` when a platform/topology condition is not met; never
   use bare `return` as a silent skip
+- [ ] No separator comments (`# ---- Section ----`); needing them signals the file/class is too
+  large and should be split
 
 ---
 
@@ -198,6 +200,10 @@ from __future__ import annotations # Remove when switching to Python 3.10+.
 
 Refer to callables as `'configure()'`, `'close()'`; non-callables as `'outdir'`, `'_pman'`.
 
+Do not use separator/divider comments (e.g., `# ---- Section ----`) to split a file or class into
+sections. If a file or class feels large enough to need visual separators, it should be refactored
+into smaller files or classes instead.
+
 Violation regex: `^\s*#[^#].*[^.]$`
 
 ---

CONTRIBUTING.md

@@ -537,6 +537,22 @@ When referring to a function, method, or other identifier in a comment, use sing
 parentheses for callables: `'configure()'`, `'close()'`. For non-callables, use single quotes
 without parentheses: `'outdir'`, `'_pman'`.
 
+### No Separator Comments
+
+Do not use separator or divider comments to split a file or class into visual sections:
+
+```python
+# WRONG: separator comment.
+# ---------- Set functions ------------------
+
+# WRONG: any variation of a visual divider.
+# ============================================
+# ############################################
+```
+
+If a file or class feels large enough to need such separators, treat it as a signal that the code
+should be refactored into smaller files or classes instead.
+
 ### Messages
 
 #### Small vs Capital Letters in Messages