fix(app): preserve featureless build support

The shared with_shutdown_flag helper, and the AtomicBool/Arc/
install_signal_handler imports it uses, only exist when at least one
applet feature (client, server, tui) is enabled. Gate them accordingly
instead of leaving them unconditionally compiled, which broke
`--no-default-features` workspace CI under -D warnings (unused
function/dead-code).

Also correct the README installation section: tui is already part of
the default feature set, so an ordinary `cargo install` already
produces irtt-tui alongside the other three binaries. Document a
lightweight `--no-default-features --features client` install instead
of the previous (incorrect) framing of tui as an opt-in extra, and fix
the same gap in the binaries/features table.

README.md

@@ -38,12 +38,14 @@ This installs:
 
 * `irtt-rs`, the canonical multi-applet dispatcher
 * `irtt-client`, the stream and text client
+* `irtt-tui`, the terminal UI
 * `irtt-server`, the UDP server
 
-To also install the optional terminal UI:
+Each applet can also be built in isolation with `--no-default-features` plus
+the applet's own feature. For example, a lightweight client-only install:
 
 ```sh
-cargo install --path crates/irtt-app --features tui
+cargo install --path crates/irtt-app --no-default-features --features client
 ```
 
 ## Quick start
@@ -311,13 +313,13 @@ synchronous callers. Callers that already own Tokio can drive
 
 ## Binaries and features
 
-| Build                                     | Binaries                                          |
-| ----------------------------------------- | ------------------------------------------------- |
-| `--no-default-features`                   | `irtt-rs`                                         |
-| `--no-default-features --features server` | `irtt-rs`, `irtt-server`                          |
-| Default features                          | `irtt-rs`, `irtt-client`, `irtt-server`           |
-| `--features tui`                          | `irtt-rs`, `irtt-client`, `irtt-server`, `irtt-tui` |
-| `--all-features`                          | `irtt-rs`, `irtt-client`, `irtt-server`, `irtt-tui` |
+| Build                                       | Binaries                                            |
+| -------------------------------------------- | --------------------------------------------------- |
+| `--no-default-features`                     | `irtt-rs`                                           |
+| `--no-default-features --features client`   | `irtt-rs`, `irtt-client`                            |
+| `--no-default-features --features server`   | `irtt-rs`, `irtt-server`                            |
+| `--no-default-features --features tui`      | `irtt-rs`, `irtt-tui`                               |
+| Default features (or `--all-features`)      | `irtt-rs`, `irtt-client`, `irtt-tui`, `irtt-server`  |
 
 `irtt-client` requires the `client` feature, `irtt-server` the `server` feature,
 and `irtt-tui` the `tui` feature. The `irtt-rs` dispatcher is always built, and

crates/irtt-app/src/entry.rs

@@ -1,14 +1,10 @@
-use std::{
-    env,
-    ffi::OsString,
-    process::ExitCode,
-    sync::{atomic::AtomicBool, Arc},
-};
+#[cfg(any(feature = "client", feature = "server", feature = "tui"))]
+use std::sync::{atomic::AtomicBool, Arc};
+use std::{env, ffi::OsString, process::ExitCode};
 
-use crate::{
-    applet::{dispatch_from_argv, AppletDispatch, RequestedApplet},
-    signal::install_signal_handler,
-};
+use crate::applet::{dispatch_from_argv, AppletDispatch, RequestedApplet};
+#[cfg(any(feature = "client", feature = "server", feature = "tui"))]
+use crate::signal::install_signal_handler;
 
 /// Entry point for the `irtt-rs` multicall dispatcher binary.
 ///
@@ -81,6 +77,7 @@ fn run_dispatcher_from_env() -> Result<(), Box<dyn std::error::Error>> {
 
 /// Installs the shutdown signal handler shared by every applet and hands the
 /// resulting flag to `f`.
+#[cfg(any(feature = "client", feature = "server", feature = "tui"))]
 fn with_shutdown_flag(
     f: impl FnOnce(&AtomicBool) -> Result<(), Box<dyn std::error::Error>>,
 ) -> Result<(), Box<dyn std::error::Error>> {