fix(ssh): log in as this machine's user when a host leaves User blank

The form says a blank User is resolved at connect, and the host card shows
$USER, but the empty string went to the server as the user name. sshd
refused it as an invalid user and tty7 reported every key as rejected.

crates/tty7-core/src/core/ssh_profile.rs

@@ -263,6 +263,22 @@ fn try_parse_port(s: &str) -> Option<u16> {
     s.parse::<u16>().ok().filter(|&p| p != 0)
 }
 
+/// The user a profile logs in as: its own, or — left blank, as the form's
+/// "resolved at connect" says — this machine's login name, the way `ssh`
+/// itself does. Sending the blank on was an empty user name the server
+/// refused, reported as every key being rejected.
+pub fn login_user(profile_user: &str) -> String {
+    if !profile_user.trim().is_empty() {
+        return profile_user.to_string();
+    }
+    ["USER", "LOGNAME", "USERNAME"]
+        .iter()
+        .filter_map(|var| std::env::var(var).ok())
+        .map(|name| name.trim().to_string())
+        .find(|name| !name.is_empty())
+        .unwrap_or_default()
+}
+
 pub fn to_connect_string(profile: &SshProfile) -> String {
     let host = if profile.host.contains(':') {
         format!("[{}]", profile.host)
@@ -366,6 +382,14 @@ fn default_identity_candidates_in(home: &str) -> Vec<String> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn a_blank_user_logs_in_as_this_machines_user() {
+        assert_eq!(login_user("deploy"), "deploy");
+        let here = login_user("");
+        assert!(!here.is_empty(), "a blank user must resolve to someone");
+        assert_eq!(login_user("  "), here);
+    }
+
     #[test]
     fn profiles_saved_before_the_switch_existed_default_to_integrated() {
         let profile: SshProfile =

src/ui/ssh_connect.rs

@@ -429,7 +429,7 @@ fn build_spec_inner(
     NativeSshSpec {
         host: profile.host.clone(),
         port: profile.port,
-        user: profile.user.clone(),
+        user: crate::core::ssh_profile::login_user(&profile.user),
         auth_mode: map_auth_mode(profile.auth),
         identity_files,
         agent_forward: profile.agent_forward,