The execution sandbox stops the agent from breaking out during development, but the real risk is what gets shipped downstream. Seeing more tools now that scan the generated code itself, not just contain the execution environment.
Sandboxes provide a "default-deny policy" which is the right starting point. But, current tools lack the right primitives to make fine grained data-access and data policy a reality.
Object-capabilities provide the primitive for fine-grained access. IFC (information flow control) for dataflow.