diff --git a/CLAUDE.md b/CLAUDE.md
index 5d62d2cdcd..5395d6d938 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -91,6 +91,10 @@ LiteLLM is a unified interface for 100+ LLM providers with two main components:
 - Async/await patterns throughout
 - Type hints required for all public APIs
 - **Avoid imports within methods** — place all imports at the top of the file (module-level). Inline imports inside functions/methods make dependencies harder to trace and hurt readability. The only exception is avoiding circular imports where absolutely necessary.
+- **Use dict spread for immutable copies** — prefer `{**original, "key": new_value}` over `dict(obj)` + mutation. The spread produces the final dict in one step and makes intent clear.
+- **Guard at resolution time** — when resolving an optional value through a fallback chain (`a or b or ""`), raise immediately if the resolved result being empty is an error. Don't pass empty strings or sentinel values downstream for the callee to deal with.
+- **Extract complex comprehensions to named helpers** — a set/dict comprehension that calls into the DB or manager (e.g. "which of these server IDs are OAuth2?") belongs in a named helper function, not inline in the caller.
+- **FastAPI parameter declarations** — mark required query/form params with `= Query(...)` / `= Form(...)` explicitly when other params in the same handler are optional. Mixing `str` (required) with `Optional[str] = None` in the same signature causes silent 422s when the required param is missing.
 
 ### Testing Strategy
 - Unit tests in `tests/test_litellm/`
@@ -98,6 +102,8 @@ LiteLLM is a unified interface for 100+ LLM providers with two main components:
 - Proxy tests in `tests/proxy_unit_tests/`
 - Load tests in `tests/load_tests/`
 - **Always add tests when adding new entity types or features** — if the existing test file covers other entity types, add corresponding tests for the new one
+- **Keep monkeypatch stubs in sync with real signatures** — when a function gains a new optional parameter, update every `fake_*` / `stub_*` in tests that patch it to also accept that kwarg (even as `**kwargs`). Stale stubs fail with `unexpected keyword argument` and mask real bugs.
+- **Test all branches of name→ID resolution** — when adding server/resource lookup that resolves names to UUIDs, test: (1) name resolves and UUID is allowed, (2) name resolves but UUID is not allowed, (3) name does not resolve at all. The silent-fallback path is where access-control bugs hide.
 
 ### UI / Backend Consistency
 - When wiring a new UI entity type to an existing backend endpoint, verify the backend API contract (single value vs. array, required vs. optional params) and ensure the UI controls match — e.g., use a single-select dropdown when the backend accepts a single value, not a multi-select