@spec key_from_command([String.t()]) :: String.t() | nil

Extracts the first key from a Redis command for slot routing.

@spec keys_from_command([String.t()]) :: [String.t()]

Extracts the keys referenced by a command.

Commands with dynamic key positions (such as EVAL, XREAD, and the *MPOP family) and common multi-key commands are handled explicitly. Unknown commands fall back to Redis' usual first-argument key convention.

@spec slot(String.t()) :: non_neg_integer()

Computes the hash slot for a key.

@spec slot_for_command([String.t()]) ::
  {:ok, non_neg_integer()} | {:error, :no_key} | {:error, :cross_slot}

Extracts all keys from a command. For multi-key commands, validates they all hash to the same slot. Returns {:ok, slot} or {:error, :cross_slot}.

@spec validate_pipeline([[String.t()]]) ::
  {:ok, non_neg_integer()}
  | {:error, :cross_slot}
  | {:error, :empty}
  | {:error, :no_key}

Validates that all commands in a pipeline target the same slot.