Whether FilesystemMiddleware may use capture-at-source offload for execute.
When True, large execute output is captured to a file in the sandbox and
only a preview is returned, avoiding a round-trip back through the agent
process. Defaults to False (opt-in) because the capture wrapper's shell and
coreutils assumptions are not guaranteed on every sandbox image; subclasses
known to be compatible set it to True. When False, execute_with_offload
runs the command unwrapped and the middleware falls back to inline execution
plus generic eviction.
