Prevent `rad` from panicking when its stdout is a closed pipe, e.g.
when running `rad config | head`.
The broken pipes are handled at the output boundaries using three
layers of defence:
1. Inner: Route all stdout output through `term::print()` and
`term::print_inline()`, which use explicit `writeln!`/`write!` to
a locked stdout and silently ignore write errors. All `println!`
calls in `radicle-cli` and `radicle-term` are converted.
2. Middle: Catch `BrokenPipe` errors that propagate up via `anyhow`
from subcommands in `main::run()`, and exit cleanly with code 0.
3. Outer: Install a panic hook that intercepts `println!` panics
containing "Broken pipe" (from dependencies like clap) and exits
cleanly, chained in front of human_panic's hook.
To prevent regressions, `#![deny(clippy::print_stdout)]` is added to
`radicle-cli`, requiring all future stdout output to go through the
safe `term::` functions.
Note: `eprintln!` calls (stderr) are not handled, as broken stderr
pipes are extremely rare in practice.
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