fix(updater): package installs update through their package manager

On CachyOS the in-app update failed with "Permission denied (os error 13)
at path /usr/bin/tauri_current_app…": the app was installed from the
Arch package, and Tauri's Linux updater can only replace an AppImage — for
anything else it tries to write next to the binary in /usr/bin.

- update_install_kind command: "in-app" on Windows and for an AppImage
  ($APPIMAGE set); on Linux package installs "pacman" (ID/ID_LIKE arch:
  Arch, CachyOS, Manjaro, EndeavourOS…), "deb" (debian/ubuntu and
  derivatives) or "manual". The web UI shows the matching update command.
- install_update refuses up front on a package install
  ("install: package-managed (…)") instead of downloading the whole
  update and failing at the last step.

Tests: CachyOS/Arch → pacman; Ubuntu/Debian/Mint → deb; Fedora/unknown →
manual; AppImage and Windows → in-app.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src-tauri/src/lib.rs

@@ -189,6 +189,47 @@ mod update_retry {
     }
 }
 
+/// How this copy of the app gets updated.
+///
+/// Tauri's updater can replace the Windows install and a Linux AppImage, but
+/// not a copy installed by a package manager: it tries to write next to the
+/// binary in /usr/bin and fails with "Permission denied (os error 13)"
+/// (reported on CachyOS). Those installs update through their package
+/// manager instead; the web UI shows the right command.
+pub(crate) fn install_kind(linux: bool, appimage: bool, os_release: &str) -> &'static str {
+    if !linux || appimage {
+        return "in-app";
+    }
+    let field = |key: &str| {
+        os_release
+            .lines()
+            .find_map(|l| l.strip_prefix(key).and_then(|v| v.strip_prefix('=')))
+            .map(|v| v.trim().trim_matches('"').to_ascii_lowercase())
+            .unwrap_or_default()
+    };
+    let ids = format!("{} {}", field("ID"), field("ID_LIKE"));
+    let has = |name: &str| ids.split_whitespace().any(|w| w == name);
+    if has("arch") {
+        "pacman"
+    } else if has("debian") || has("ubuntu") {
+        "deb"
+    } else {
+        "manual"
+    }
+}
+
+#[tauri::command]
+fn update_install_kind() -> &'static str {
+    let linux = cfg!(target_os = "linux");
+    let appimage = std::env::var_os("APPIMAGE").is_some();
+    let os_release = if linux {
+        std::fs::read_to_string("/etc/os-release").unwrap_or_default()
+    } else {
+        String::new()
+    };
+    install_kind(linux, appimage, &os_release)
+}
+
 #[tauri::command]
 async fn check_for_update(app: tauri::AppHandle) -> Result<UpdateInfo, String> {
     #[cfg(not(any(target_os = "android", target_os = "ios")))]
@@ -211,6 +252,15 @@ async fn install_update(app: tauri::AppHandle) -> Result<(), String> {
     {
         use std::time::{Duration, Instant};
 
+        // A package-manager install can't be replaced in place (see
+        // install_kind); refuse before downloading anything.
+        let kind = update_install_kind();
+        if kind != "in-app" {
+            return Err(format!(
+                "install: package-managed ({kind}): update Lotus Chat with your package manager"
+            ));
+        }
+
         let emit = |detail: serde_json::Value| {
             native::emit_to_web(&app, "lotus-update-progress", &detail.to_string());
         };
@@ -939,6 +989,7 @@ pub fn run() {
             send_notification,
             check_for_update,
             install_update,
+            update_install_kind,
             native::power::set_call_active,
             native::jumplist::set_jump_list,
             native::thumbbar::set_thumbbar,
@@ -1333,6 +1384,36 @@ mod webview2_args_tests {
     }
 }
 
+#[cfg(test)]
+mod install_kind_tests {
+    use super::install_kind;
+
+    #[test]
+    fn package_installs_update_through_their_package_manager() {
+        let cachy = "NAME=\"CachyOS Linux\"\nID=cachyos\nID_LIKE=arch\n";
+        let arch = "NAME=\"Arch Linux\"\nID=arch\n";
+        let ubuntu = "NAME=\"Ubuntu\"\nID=ubuntu\nID_LIKE=debian\n";
+        let debian = "ID=debian\n";
+        let mint = "ID=linuxmint\nID_LIKE=\"ubuntu debian\"\n";
+        let fedora = "ID=fedora\n";
+        assert_eq!(install_kind(true, false, cachy), "pacman");
+        assert_eq!(install_kind(true, false, arch), "pacman");
+        assert_eq!(install_kind(true, false, ubuntu), "deb");
+        assert_eq!(install_kind(true, false, debian), "deb");
+        assert_eq!(install_kind(true, false, mint), "deb");
+        assert_eq!(install_kind(true, false, fedora), "manual");
+        assert_eq!(install_kind(true, false, ""), "manual");
+        // ID_LIKE mentioning arch only as part of a longer word doesn't count.
+        assert_eq!(install_kind(true, false, "ID=x\nID_LIKE=archlike\n"), "manual");
+    }
+
+    #[test]
+    fn appimage_and_windows_update_in_app() {
+        assert_eq!(install_kind(true, true, "ID=cachyos\nID_LIKE=arch\n"), "in-app");
+        assert_eq!(install_kind(false, false, ""), "in-app");
+    }
+}
+
 #[cfg(test)]
 mod tray_tests {
     use super::*;