alt Hacker Newssandboxing is indeed an advantage (can be an important one!), but
1. bash can also express concurrency easily, with sync and async (using standard & syntax) support for each command, and standard cancellation (kill, though crude). 2. "way fewer instructions": It requires no instruction for agents to use bash either, except for merely listing the custom commands (view_image, apply_patch, etc.). Also, bash has standard progressive disclosure mechanism (--help) that models will automatically use with no instruction.
We might be talking past each other here. The point of codemode is to orchestrate the LLM side tool calls, not to orchestrate scripts that it might execute within Bash.
In a world where brain and hand are on different machines, getting the bash hands to reach back into the harness brain is something that requires a) putting tools in its hands that it does not know about b) are tricky to set up, usually involving some sort of socket based back channel.
I tried this quite a bit, by having pi be always there on the hands side, but it causes a lot of complexity and the LLMs really do not understand it well at all.