Per-request wrapper over PlatformEntitiesClient extracted from Launch Pipeline:
reads (inventory/product/shop_names) cached by (user_key, op, arg) with TTL,
writes invalidate the user cache; token=None -> PlatformTokenMissingError,
auth failure -> PlatformTokenRejectedError(mode). TtlCache injectable,
reset_default_cache() for test fixtures.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>