feat(kiosk): display-size presets in Settings (Auto/Large/Balanced/Native)

system.kiosk-display.get/set RPCs write /etc/archipelago/kiosk-display.conf
(sourced by the kiosk launcher) and try-restart the kiosk so the choice
applies immediately. The Settings section only appears on nodes that have
the kiosk unit installed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/dispatcher.rs

@@ -456,6 +456,8 @@ impl RpcHandler {
             "system.factory-reset" => self.handle_system_factory_reset(params).await,
             "system.settings.get" => self.handle_system_settings_get(params).await,
             "system.settings.set" => self.handle_system_settings_set(params).await,
+            "system.kiosk-display.get" => self.handle_system_kiosk_display_get().await,
+            "system.kiosk-display.set" => self.handle_system_kiosk_display_set(params).await,
 
             // Opt-in anonymous analytics
             "analytics.get-status" => self.handle_analytics_get_status().await,

core/archipelago/src/api/rpc/system/handlers.rs

@@ -719,4 +719,94 @@ impl RpcHandler {
             _ => anyhow::bail!("Unknown setting: {}", key),
         }
     }
+
+    /// system.kiosk-display.get — Current kiosk display preset + whether this
+    /// node has a kiosk at all (no kiosk unit -> the Settings section hides).
+    pub(in crate::api::rpc) async fn handle_system_kiosk_display_get(
+        &self,
+    ) -> Result<serde_json::Value> {
+        let has_kiosk = tokio::fs::metadata("/etc/systemd/system/archipelago-kiosk.service")
+            .await
+            .is_ok();
+        let conf = tokio::fs::read_to_string(KIOSK_DISPLAY_CONF)
+            .await
+            .unwrap_or_default();
+        let preset = if conf.contains("ARCHIPELAGO_KIOSK_SCALE=1") {
+            "native"
+        } else if conf.contains("ARCHIPELAGO_KIOSK_TARGET_CSS_WIDTH=1920") {
+            "balanced"
+        } else if conf.contains("ARCHIPELAGO_KIOSK_TARGET_CSS_WIDTH=1280") {
+            "large"
+        } else {
+            "auto"
+        };
+        Ok(serde_json::json!({ "has_kiosk": has_kiosk, "preset": preset }))
+    }
+
+    /// system.kiosk-display.set — Write the kiosk display preset and restart
+    /// the kiosk (only if it is running) so it takes effect immediately. The
+    /// launcher sources /etc/archipelago/kiosk-display.conf at startup.
+    pub(in crate::api::rpc) async fn handle_system_kiosk_display_set(
+        &self,
+        params: Option<serde_json::Value>,
+    ) -> Result<serde_json::Value> {
+        let params = params.ok_or_else(|| anyhow::anyhow!("Missing params"))?;
+        let preset = params
+            .get("preset")
+            .and_then(|v| v.as_str())
+            .ok_or_else(|| anyhow::anyhow!("Missing preset"))?;
+
+        let conf = match preset {
+            // Resolution-derived default: 4K -> 2.0 (1920-wide layout),
+            // 1080p TV -> 1.5, laptop panels -> 1.0.
+            "auto" => String::new(),
+            // Biggest UI: every panel targets a 1280-wide layout.
+            "large" => "ARCHIPELAGO_KIOSK_TARGET_CSS_WIDTH=1280\n".to_string(),
+            // Full-HD layout on any panel that can carry it.
+            "balanced" => "ARCHIPELAGO_KIOSK_TARGET_CSS_WIDTH=1920\n".to_string(),
+            // No scaling: native CSS viewport, most content, smallest UI.
+            "native" => "ARCHIPELAGO_KIOSK_SCALE=1\n".to_string(),
+            other => anyhow::bail!("Unknown display preset: {other}"),
+        };
+
+        host_sudo(&["/usr/bin/mkdir", "-p", "/etc/archipelago"]).await?;
+        if conf.is_empty() {
+            let _ = host_sudo(&["/usr/bin/rm", "-f", KIOSK_DISPLAY_CONF]).await;
+        } else {
+            // tee via sudo — the backend runs unprivileged and /etc is root's.
+            let mut child = tokio::process::Command::new("/usr/bin/sudo")
+                .args(["-n", "/usr/bin/tee", KIOSK_DISPLAY_CONF])
+                .stdin(std::process::Stdio::piped())
+                .stdout(std::process::Stdio::null())
+                .stderr(std::process::Stdio::piped())
+                .spawn()
+                .context("spawn sudo tee for kiosk display conf")?;
+            use tokio::io::AsyncWriteExt;
+            if let Some(mut stdin) = child.stdin.take() {
+                stdin.write_all(conf.as_bytes()).await?;
+            }
+            let out = child.wait_with_output().await?;
+            if !out.status.success() {
+                anyhow::bail!(
+                    "writing {} failed: {}",
+                    KIOSK_DISPLAY_CONF,
+                    String::from_utf8_lossy(&out.stderr).trim()
+                );
+            }
+        }
+
+        // try-restart: only bounces a kiosk that is actually running, so this
+        // never starts a kiosk an operator disabled.
+        let _ = host_sudo(&[
+            "/usr/bin/systemctl",
+            "try-restart",
+            "archipelago-kiosk.service",
+        ])
+        .await;
+
+        info!(preset, "Kiosk display preset applied");
+        Ok(serde_json::json!({ "preset": preset, "applied": true }))
+    }
 }
+
+const KIOSK_DISPLAY_CONF: &str = "/etc/archipelago/kiosk-display.conf";