Correct the `shell` tool description for sandboxed runs and add targeted
tests.
- Fix the WorkspaceWrite description to clearly state that writes
outside the writable roots require escalated permissions; reads are not
restricted. The previous wording/formatting could be read as restricting
reads outside the workspace.
- Render the writable roots list on its own lines under a newline after
"writable roots:" for clarity.
- Show the "Commands that require network access" note only in
WorkspaceWrite when network is disabled.
- Add focused tests that call `create_shell_tool_for_sandbox` directly
and assert the exact description text for WorkspaceWrite, ReadOnly, and
DangerFullAccess.
- Update AGENTS.md to note that `just fmt` can be run automatically
without asking.