Add optional command extensions

README.md

@@ -165,6 +165,29 @@ in Dosh's host config:
 dosh import-ssh palav homelab
 ```
 
+Optional command extensions are just config-side startup shortcuts; Dosh has no
+compile-time dependency on the tools they run. For example, to make a separately
+installed server-side `tm` dashboard easy to open:
+
+```toml
+# ~/.config/dosh/client.toml
+[extensions.tm]
+command = "tm {args}"
+description = "Open the server-side tmux dashboard"
+```
+
+Then `dosh palav tm` sends `tm`, and `dosh palav tm dosh` sends `tm 'dosh'`.
+Remove that table to remove the integration. Hosts can override or opt out:
+
+```toml
+# ~/.config/dosh/hosts.toml
+[palav.extensions.tm]
+command = "/opt/tm/bin/tm {args}"
+
+[other-host.extensions.tm]
+disabled = true
+```
+
 ## Develop
 
 Build:

docs/NATIVE_V1_SPEC.md

@@ -51,6 +51,7 @@ dosh -L 8080:127.0.0.1:80 host
 dosh -R 9000:127.0.0.1:9000 host
 dosh --session work host
 dosh --view-only --session work host
+dosh host tm
 ```
 
 Compatibility expectations:
@@ -107,6 +108,8 @@ Must work in v1:
 - `dosh update`.
 - `dosh doctor host` for config/auth/UDP reachability diagnostics.
 - `dosh sessions host` for session visibility.
+- Optional command extensions such as `dosh host tm` for companion tools that are
+  installed separately from Dosh.
 
 Should work in v1 if it does not compromise the transport schedule:
 
@@ -556,6 +559,10 @@ forward_agent = false
 send_env = ["LANG", "LC_*", "TERM", "COLORTERM"]
 set_env = {}
 forwardings = []
+
+[extensions.tm]
+command = "tm {args}"
+description = "Open an optional server-side tmux dashboard"
 ```
 
 Server:

docs/PUBLIC_READINESS.md

@@ -101,6 +101,29 @@ dosh import-ssh palav homelab
 This appends entries to `~/.config/dosh/hosts.toml` without trying to become an
 OpenSSH config parser.
 
+## Optional Command Extensions
+
+Dosh can expose companion tools without taking a dependency on them. Command
+extensions live in client or host config and expand only the first trailing word:
+
+```toml
+[extensions.tm]
+command = "tm {args}"
+description = "Open the server-side tmux dashboard"
+```
+
+With that config, `dosh palav tm` runs `tm` in the remote Dosh shell and
+`dosh palav tm dosh` runs `tm 'dosh'`. Removing the table removes the integration.
+Host config can override a global extension, or disable it:
+
+```toml
+[palav.extensions.tm]
+command = "/opt/tm/bin/tm {args}"
+
+[other-host.extensions.tm]
+disabled = true
+```
+
 ## Forwarding (Implemented)
 
 SSH forwarding cannot be copied by keeping the bootstrap SSH connection open,

src/bin/dosh-client.rs

@@ -212,11 +212,7 @@ async fn main() -> Result<()> {
         .unwrap_or_default();
     let raw_server = host.ssh.clone().unwrap_or_else(|| requested_server.clone());
     let server = ssh_with_user(&raw_server, host.user.as_deref());
-    let startup_command = startup_command(&args.command).or_else(|| {
-        host.default_command
-            .as_deref()
-            .map(startup_command_from_string)
-    });
+    let startup_command = resolved_startup_command(&args.command, &config, &host);
     let local_forwards = parse_local_forwards(&args.local_forward)?;
     let remote_forwards = parse_remote_forwards(&args.remote_forward)?;
     let dynamic_forwards = parse_dynamic_forwards(&args.dynamic_forward)?;
@@ -776,6 +772,73 @@ fn startup_command(args: &[String]) -> Option<Vec<u8>> {
     Some(command.into_bytes())
 }
 
+fn resolved_startup_command(
+    args: &[String],
+    config: &dosh::config::ClientConfig,
+    host: &dosh::config::HostConfig,
+) -> Option<Vec<u8>> {
+    if args.is_empty() {
+        return host
+            .default_command
+            .as_deref()
+            .map(startup_command_from_string);
+    }
+    match resolve_command_extension(args, config, host) {
+        ExtensionResolution::Command(command) => Some(startup_command_from_string(&command)),
+        ExtensionResolution::Disabled => None,
+        ExtensionResolution::NoMatch => startup_command(args),
+    }
+}
+
+enum ExtensionResolution {
+    Command(String),
+    Disabled,
+    NoMatch,
+}
+
+fn resolve_command_extension(
+    args: &[String],
+    config: &dosh::config::ClientConfig,
+    host: &dosh::config::HostConfig,
+) -> ExtensionResolution {
+    let Some(name) = args.first() else {
+        return ExtensionResolution::NoMatch;
+    };
+    if let Some(extension) = host.extensions.get(name) {
+        if extension.disabled {
+            return ExtensionResolution::Disabled;
+        }
+        if let Some(command) = extension.command.as_deref() {
+            return ExtensionResolution::Command(expand_command_extension(command, &args[1..]));
+        }
+    }
+    if let Some(extension) = config.extensions.get(name) {
+        if extension.disabled {
+            return ExtensionResolution::Disabled;
+        }
+        if let Some(command) = extension.command.as_deref() {
+            return ExtensionResolution::Command(expand_command_extension(command, &args[1..]));
+        }
+    }
+    ExtensionResolution::NoMatch
+}
+
+fn expand_command_extension(template: &str, args: &[String]) -> String {
+    let quoted_args = args
+        .iter()
+        .map(|arg| shell_word(arg))
+        .collect::<Vec<_>>()
+        .join(" ");
+    if template.contains("{args}") {
+        return template.replace("{args}", &quoted_args);
+    }
+    if args.is_empty() {
+        template.to_string()
+    } else {
+        format!("{template} {quoted_args}")
+    }
+}
+
 fn startup_command_from_string(command: &str) -> Vec<u8> {
     let mut command = command.to_string();
     command.push('\n');
@@ -4226,10 +4289,11 @@ mod tests {
         RemoteForward, SshConfig, StatusAction, auth_allows,
         load_first_native_identity_with_prompt, parse_dynamic_forward, parse_local_forward,
         parse_remote_forward, parse_ssh_config, raw_contains_host_table, recv_response_until,
-        render_status_clear, render_status_overlay, requested_env, ssh_destination_host,
-        ssh_username, ssh_with_user, startup_command, toml_bare_key_or_quoted,
+        render_status_clear, render_status_overlay, requested_env, resolved_startup_command,
+        ssh_destination_host, ssh_username, ssh_with_user, startup_command,
+        toml_bare_key_or_quoted,
     };
-    use dosh::config::{ClientConfig, HostConfig};
+    use dosh::config::{ClientConfig, CommandExtension, HostConfig};
     use dosh::native::EnvVar;
     use dosh::protocol::{self, Frame, PacketKind};
     use ed25519_dalek::{SigningKey, VerifyingKey};
@@ -4775,6 +4839,100 @@ mod tests {
         );
     }
 
+    #[test]
+    fn resolved_startup_command_expands_global_extension() {
+        let mut config = ClientConfig::default();
+        config.extensions.insert(
+            "tm".to_string(),
+            CommandExtension {
+                command: Some("tm {args}".to_string()),
+                description: Some("server tmux dashboard".to_string()),
+                disabled: false,
+            },
+        );
+        let host = HostConfig::default();
+
+        assert_eq!(
+            resolved_startup_command(&["tm".into(), "work space".into()], &config, &host),
+            Some(b"tm 'work space'\n".to_vec())
+        );
+    }
+
+    #[test]
+    fn resolved_startup_command_uses_host_extension_override() {
+        let mut config = ClientConfig::default();
+        config.extensions.insert(
+            "tm".to_string(),
+            CommandExtension {
+                command: Some("tm {args}".to_string()),
+                description: None,
+                disabled: false,
+            },
+        );
+        let mut host = HostConfig::default();
+        host.extensions.insert(
+            "tm".to_string(),
+            CommandExtension {
+                command: Some("/opt/tm/bin/tm --remote {args}".to_string()),
+                description: None,
+                disabled: false,
+            },
+        );
+
+        assert_eq!(
+            resolved_startup_command(&["tm".into(), "dosh".into()], &config, &host),
+            Some(b"/opt/tm/bin/tm --remote 'dosh'\n".to_vec())
+        );
+    }
+
+    #[test]
+    fn resolved_startup_command_host_can_disable_global_extension() {
+        let mut config = ClientConfig::default();
+        config.extensions.insert(
+            "tm".to_string(),
+            CommandExtension {
+                command: Some("tm {args}".to_string()),
+                description: None,
+                disabled: false,
+            },
+        );
+        let mut host = HostConfig::default();
+        host.extensions.insert(
+            "tm".to_string(),
+            CommandExtension {
+                command: None,
+                description: None,
+                disabled: true,
+            },
+        );
+
+        assert_eq!(
+            resolved_startup_command(&["tm".into(), "dosh".into()], &config, &host),
+            None
+        );
+    }
+
+    #[test]
+    fn resolved_startup_command_keeps_raw_command_fallback_and_default_command() {
+        let config = ClientConfig::default();
+        let mut host = HostConfig {
+            default_command: Some("tm".to_string()),
+            ..HostConfig::default()
+        };
+
+        assert_eq!(
+            resolved_startup_command(&["echo".into(), "ok".into()], &config, &host),
+            Some(b"echo ok\n".to_vec())
+        );
+        assert_eq!(
+            resolved_startup_command(&[], &config, &host),
+            Some(b"tm\n".to_vec())
+        );
+
+        host.default_command = None;
+        assert_eq!(resolved_startup_command(&[], &config, &host), None);
+    }
+
     #[test]
     fn parses_local_forward_with_default_bind() {
         assert_eq!(

src/config.rs

@@ -136,6 +136,11 @@ pub struct ClientConfig {
     pub send_env: Vec<String>,
     #[serde(default)]
     pub set_env: HashMap<String, String>,
+    /// Optional client-side command extensions. These are just shell command
+    /// templates expanded into the remote session's startup input; Dosh does not
+    /// depend on the tools they name.
+    #[serde(default)]
+    pub extensions: HashMap<String, CommandExtension>,
 }
 
 #[derive(Debug, Clone, Default, Serialize, Deserialize)]
@@ -151,6 +156,22 @@ pub struct HostConfig {
     pub send_env: Option<Vec<String>>,
     #[serde(default)]
     pub set_env: HashMap<String, String>,
+    /// Per-host extension overrides. A host can replace a global extension or set
+    /// `disabled = true` to opt out of it.
+    #[serde(default)]
+    pub extensions: HashMap<String, CommandExtension>,
+}
+
+#[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq, Eq)]
+pub struct CommandExtension {
+    /// Remote shell command template. `{args}` expands to shell-quoted extra
+    /// words after the extension name. When absent, extra args are appended.
+    #[serde(default)]
+    pub command: Option<String>,
+    #[serde(default)]
+    pub description: Option<String>,
+    #[serde(default)]
+    pub disabled: bool,
 }
 
 #[derive(Debug, Clone, Default, Serialize, Deserialize)]
@@ -186,6 +207,7 @@ impl Default for ClientConfig {
             disconnect_status: true,
             send_env: default_send_env(),
             set_env: HashMap::new(),
+            extensions: HashMap::new(),
         }
     }
 }