## What changed
- Remove the legacy `shell_command` handler and runtime, leaving `exec_command`
and `write_stdin` as the shell execution tools.
- Treat legacy `shell_command` model metadata as `unified_exec`, and normalize
legacy user opt-outs so they do not disable command execution. Managed feature
requirements and `shell_tool` can still disable it.
- Preserve shell approvals, sandboxing, zsh-fork support, and output truncation
through the unified execution path.
## Testing
- Cover legacy configuration and model-metadata compatibility.
- Exercise unified shell execution, approvals, truncation, and `apply_patch`
serialization across the app-server and core test suites.
GitOrigin-RevId: 5c2fd6164fc3519cdae4944cb9db276b8467311c
8a40095ea3