No production LeafSpec uses LeafInt64; devapp only needs LeafInt
(non-zero-only putInt semantics). The default MCP dispatch and Server
routing stay — they are the framework's documented main path for
future MCP-direct products.
Plain Required now validates the effective value (primary flag -> aliases
-> env) instead of only the primary flag, matching the declared fallback
semantics; whitespace-only values under Trim count as missing. Extracted
cmdutil.MissingRequiredFlagsError to keep the unified error format.