Keep carrier handling inside publication ownership

Keep carrier handling inside publication ownership复制锚点链接

Command mounts accept { install, handle? } instead of an installer callback. The optional handler receives the captured Command, untrusted input, and carrier context; authorization, context projection, execution, and response presentation settle within the provider and publisher invocations. A custom handler can project its own output type and construct a command-specific context. Direct bindings still execute the selected Command unchanged.

Mounted endpoints carry an explicit marker and cannot be re-mounted as direct definitions. The new snapshotCommand() captures and validates the descriptor and execute function without creating a temporary registry, preserving the receiver and existing publication withdrawal.