server: reject unknown startup flags

Cargo.lock

@@ -1652,7 +1652,7 @@ checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
 [[package]]
 name = "lesavka_client"
-version = "0.22.39"
+version = "0.22.40"
 dependencies = [
  "anyhow",
  "async-stream",
@@ -1686,7 +1686,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_common"
-version = "0.22.39"
+version = "0.22.40"
 dependencies = [
  "anyhow",
  "base64",
@@ -1698,7 +1698,7 @@ dependencies = [
 
 [[package]]
 name = "lesavka_server"
-version = "0.22.39"
+version = "0.22.40"
 dependencies = [
  "anyhow",
  "base64",

client/Cargo.toml

@@ -4,7 +4,7 @@ path                    = "src/main.rs"
 
 [package]
 name                    = "lesavka_client"
-version                 = "0.22.39"
+version                 = "0.22.40"
 edition                 = "2024"
 
 [dependencies]

common/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name                    = "lesavka_common"
-version = "0.22.39"
+version = "0.22.40"
 edition                 = "2024"
 build                   = "build.rs"
 

server/Cargo.toml

@@ -10,7 +10,7 @@ bench                   = false
 
 [package]
 name                    = "lesavka_server"
-version                 = "0.22.39"
+version                 = "0.22.40"
 edition                 = "2024"
 autobins                = false
 

server/src/main/entrypoint.rs

@@ -1,19 +1,37 @@
 /*──────────────── main ───────────────────────*/
-fn print_version_and_exit_requested() -> bool {
-    if std::env::args()
-        .skip(1)
-        .any(|arg| arg == "--version" || arg == "-V")
-    {
-        println!("{} {}", PKG_NAME, lesavka_server::VERSION);
-        return true;
+fn usage_line() -> &'static str {
+    "Usage: lesavka-server [--version|-V] [--help|-h]"
+}
+
+fn handle_startup_args() -> anyhow::Result<bool> {
+    let args = std::env::args().skip(1).collect::<Vec<_>>();
+    match args.as_slice() {
+        [] => Ok(false),
+        [arg] if arg == "--version" || arg == "-V" => {
+            println!("{} {}", PKG_NAME, lesavka_server::VERSION);
+            Ok(true)
+        }
+        [arg] if arg == "--help" || arg == "-h" => {
+            println!("{}", usage_line());
+            Ok(true)
+        }
+        [arg] if arg.starts_with('-') => {
+            let suggestion = if "--version".starts_with(arg.as_str()) {
+                "; did you mean --version?"
+            } else {
+                ""
+            };
+            anyhow::bail!("unknown option {arg:?}{suggestion}; {}", usage_line())
+        }
+        [arg] => anyhow::bail!("unexpected positional argument {arg:?}; {}", usage_line()),
+        _ => anyhow::bail!("too many arguments; {}", usage_line()),
     }
-    false
 }
 
 #[cfg(not(coverage))]
 #[tokio::main(worker_threads = 4)]
 async fn main() -> anyhow::Result<()> {
-    if print_version_and_exit_requested() {
+    if handle_startup_args()? {
         return Ok(());
     }
 
@@ -58,7 +76,7 @@ async fn main() -> anyhow::Result<()> {
 #[cfg(coverage)]
 #[tokio::main(worker_threads = 2)]
 async fn main() -> anyhow::Result<()> {
-    if print_version_and_exit_requested() {
+    if handle_startup_args()? {
         return Ok(());
     }
 

tests/contract/server/main/server_main_process_contract.rs

@@ -134,6 +134,33 @@ fn server_binary_reports_version_without_starting_relay() {
     }
 }
 
+#[test]
+#[serial]
+fn server_binary_rejects_truncated_version_flag_without_starting_relay() {
+    let Some(bin) = find_binary("lesavka-server") else {
+        return;
+    };
+    let output = Command::new(bin)
+        .arg("--versio")
+        .output()
+        .expect("run lesavka-server --versio");
+    assert!(
+        !output.status.success(),
+        "truncated flag should fail instead of starting a second relay"
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("unknown option")
+            && stderr.contains("did you mean --version")
+            && stderr.contains("Usage: lesavka-server"),
+        "truncated flag should produce a helpful CLI error; stderr was:\n{stderr}"
+    );
+    assert!(
+        !stderr.contains("Address already in use") && !stderr.contains("open singleton lock"),
+        "argument validation should happen before relay, log, or UVC startup; stderr was:\n{stderr}"
+    );
+}
+
 #[test]
 #[serial]
 fn server_binary_stays_up_with_missing_hid_nodes_and_current_version() {