fix: preserve plugins during live handoff

refs #893

3 files changed, 104 insertions, 0 deletions

diff --git a/docs/next/CHANGELOG.md b/docs/next/CHANGELOG.md
index 3ee3ae06..b15f009b 100644
--- a/docs/next/CHANGELOG.md
+++ b/docs/next/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+### Fixed
+- Live handoff now preserves installed plugins and no longer lets the next plugin installation overwrite the existing registry. (#893)
+
 ## [0.7.4] - 2026-07-15
 
 ### Added
diff --git a/src/app/mod.rs b/src/app/mod.rs
index a77f2536..6ea84746 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -786,6 +786,7 @@ impl App {
         let pane_id_aliases = crate::persist::handoff_pane_aliases(snapshot, &workspaces);
 
         app.no_session = false;
+        app.state.installed_plugins = load_plugin_registry(app.no_session);
         let now = Instant::now();
         if background_update_check_enabled(app.no_session, app.update_version_check_enabled) {
             app.next_auto_update_check = app
diff --git a/tests/live_handoff.rs b/tests/live_handoff.rs
index 6302ed68..b2fb9ef6 100644
--- a/tests/live_handoff.rs
+++ b/tests/live_handoff.rs
@@ -154,6 +154,7 @@ fn spawn_default_session_server(config_home: &Path, runtime_dir: &Path) -> Spawn
     cmd.arg("server");
     cmd.env("XDG_CONFIG_HOME", config_home);
     cmd.env("XDG_RUNTIME_DIR", runtime_dir);
+    cmd.env("XDG_STATE_HOME", runtime_dir.join("state"));
     cmd.env_remove("HERDR_SESSION");
     cmd.env_remove("HERDR_SOCKET_PATH");
     cmd.env_remove("HERDR_CLIENT_SOCKET_PATH");
@@ -301,6 +302,58 @@ fn wait_for_api(socket_path: &Path, timeout: Duration) {
     );
 }
 
+fn write_plugin_manifest(root: &Path, plugin_id: &str) {
+    fs::create_dir_all(root).unwrap();
+    fs::write(
+        root.join("herdr-plugin.toml"),
+        format!(
+            r#"id = "{plugin_id}"
+name = "Live handoff test"
+version = "0.1.0"
+min_herdr_version = "0.6.10"
+platforms = ["linux", "macos", "windows"]
+"#
+        ),
+    )
+    .unwrap();
+}
+
+fn link_plugin(socket_path: &Path, root: &Path) {
+    assert_ok(request(
+        socket_path,
+        serde_json::json!({
+            "id": "test:plugin:link",
+            "method": "plugin.link",
+            "params": {"path": root, "enabled": true}
+        }),
+    ));
+}
+
+fn listed_plugin_ids(socket_path: &Path) -> Vec<String> {
+    let response = request(
+        socket_path,
+        serde_json::json!({"id":"test:plugin:list","method":"plugin.list","params":{}}),
+    );
+    assert_ok(response.clone());
+    response["result"]["plugins"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .map(|plugin| plugin["plugin_id"].as_str().unwrap().to_string())
+        .collect()
+}
+
+fn saved_plugin_ids(registry_path: &Path) -> Vec<String> {
+    let mut ids =
+        serde_json::from_str::<Vec<serde_json::Value>>(&fs::read_to_string(registry_path).unwrap())
+            .unwrap()
+            .into_iter()
+            .map(|plugin| plugin["plugin_id"].as_str().unwrap().to_string())
+            .collect::<Vec<_>>();
+    ids.sort();
+    ids
+}
+
 fn wait_for_output(socket_path: &Path, pane_id: &str, needle: &str) {
     let deadline = Instant::now() + Duration::from_secs(5);
     let mut last_text = String::new();
@@ -670,6 +723,53 @@ fn live_handoff_preserves_client_socket_env_without_api_socket_env() {
 }
 
 #[test]
+fn live_handoff_preserves_installed_plugins() {
+    let _lock = test_lock();
+    let base = unique_test_dir();
+    let config_home = base.join("config");
+    let runtime_dir = base.join("runtime");
+    let api_socket = config_home.join("herdr-dev/herdr.sock");
+    let registry_path = config_home.join("herdr-dev/plugins.json");
+    let existing_plugin = base.join("plugins/existing");
+    let added_plugin = base.join("plugins/added");
+    write_plugin_manifest(&existing_plugin, "test.live-handoff-existing");
+    write_plugin_manifest(&added_plugin, "test.live-handoff-added");
+
+    let spawned = spawn_default_session_server(&config_home, &runtime_dir);
+    wait_for_socket(&api_socket, Duration::from_secs(10));
+    register_runtime_dir(&runtime_dir);
+
+    link_plugin(&api_socket, &existing_plugin);
+    assert_eq!(
+        listed_plugin_ids(&api_socket),
+        ["test.live-handoff-existing"]
+    );
+
+    assert_ok(request(
+        &api_socket,
+        serde_json::json!({"id":"test:handoff","method":"server.live_handoff","params":{}}),
+    ));
+    drop(spawned);
+    wait_for_api(&api_socket, Duration::from_secs(10));
+
+    assert_eq!(
+        listed_plugin_ids(&api_socket),
+        ["test.live-handoff-existing"]
+    );
+    link_plugin(&api_socket, &added_plugin);
+    assert_eq!(
+        saved_plugin_ids(&registry_path),
+        ["test.live-handoff-added", "test.live-handoff-existing"]
+    );
+
+    let _ = request(
+        &api_socket,
+        serde_json::json!({"id":"test:stop","method":"server.stop","params":{}}),
+    );
+    cleanup_test_base(&base);
+}
+
+#[test]
 fn live_handoff_preserves_pane_process_io() {
     let _lock = test_lock();
     let base = unique_test_dir();