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I understand the concept, but I don't get what's the advantage over adding in the prompt instructions to use a specific bash command for a specific task, acting as a "custom tool".

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The harness clamps what the agent can do. `bash` allows full code execution; a dedicated `mvn` tool might only allow `mvn compile` but not `mvn spring-boot:run`. You could probably implement this with an `allow` list attached to your `bash` tool, but by doing it this way, you can enhance the outputs or perform mandatory checks too.

For instance, Claude likes to run little Python scripts; reviewing them is tedious. Removing `bash` and adding a `python` tool would allow the harness to pre-review and grep for common harmful patterns, or run the `python` script in a `krunvm` or `muvm` to isolate it, etc. This review/isolation would be handled programatically as it's part of the harness; leaving the agent to choose what to do as a skill means the agent can conveniently forget to enforce its own checks.

Good point. There might be a small advantage if one does not want to give bash access. But general answer to "how do add custom tools like we can in pi" is "you don't". Keep it simple.

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