diff --git a/.agents/rules/python.md b/.agents/rules/python.md
index c149130fe2..21f6671b93 100644
--- a/.agents/rules/python.md
+++ b/.agents/rules/python.md
@@ -18,10 +18,22 @@
   (e.g. `[missing-import]`) over `tags = ["no-pyrefly"]`.
 * **No blanket ignores**: NEVER use bare `# type: ignore` or literal
   `# type: ignore[...]`. Use error-specific ignores instead.
+* **Ignore comments**: When adding `# pyrefly: ignore[...]` or type
+  suppressions, add an explanatory comment indicating why it is suppressed.
 * **Type assertions**: When adding assertions for type narrowing, add an
   end-of-line comment: `assert foo is not None  # type assert`.
 * **Consent for `Any`**: Require user consent before changing type annotations
   to `Any`.
+* **Union syntax (`X | None`)**: Use `X | None` instead of `typing.Optional[X]`.
+  Add `from __future__ import annotations` if necessary.
+* **Collections generics**: Use `collections.abc` (e.g., `Sequence`, `Iterable`,
+  `Iterator`, `Callable`, `Mapping`) and builtin generics (`list`, `dict`,
+  `tuple`, `set`) instead of `typing.XXX` collection types.
+
+## Runfiles
+* **Fail-fast creation**: Prefer `runfiles.CreateOrRaise()` over
+  `runfiles.Create()` followed by manual `assert` when initializing runfiles in
+  tests and runtime scripts.
 
 ## Delegating Functions
 * Module-level functions delegating to class methods should have a docstring