fix(acp): uninstall before reinstall on npx agent upgrade

Plain `npm install -g <pkg>@<version>` over an existing install does not
reliably re-resolve platform-specific optionalDependencies, leaving the
native CLI binary missing or stale (e.g. 'Native CLI binary for darwin-x64
not found' after the claude-agent-sdk upgrade). The Upgrade button now
runs npm uninstall -g first as a best-effort step, forcing npm to rebuild
the dependency graph from scratch on the subsequent install. If the clean
upgrade fails midway, the DB and the Settings UI resync to the actual
on-disk state instead of showing a phantom version.

src-tauri/src/commands/acp.rs

@@ -2735,6 +2735,7 @@ pub async fn acp_detect_agent_local_version(
 pub(crate) async fn acp_prepare_npx_agent_core(
     agent_type: AgentType,
     registry_version: Option<String>,
+    clean_first: bool,
     task_id: String,
     db: &AppDatabase,
     emitter: &EventEmitter,
@@ -2759,6 +2760,30 @@ pub(crate) async fn acp_prepare_npx_agent_core(
                 .flatten()
                 .and_then(|m| m.installed_version);
 
+            // Best-effort uninstall before reinstall. Forces npm to re-resolve
+            // the dependency graph from scratch, which is required for
+            // platform-specific optionalDependencies (e.g. native CLI binaries
+            // shipped as `<pkg>-darwin-x64`) to be picked up after an upgrade.
+            // Failures here are logged and swallowed so we still attempt the
+            // install — for example when nothing is currently installed.
+            if clean_first {
+                let package_name = package_name_from_spec(package);
+                emit_agent_install_event(
+                    emitter,
+                    &task_id,
+                    AgentInstallEventKind::Log,
+                    format!("$ npm uninstall -g {package_name} (clean reinstall)"),
+                );
+                if let Err(e) = uninstall_npm_global_package(package).await {
+                    emit_agent_install_event(
+                        emitter,
+                        &task_id,
+                        AgentInstallEventKind::Log,
+                        format!("(warning) uninstall step failed, continuing: {e}"),
+                    );
+                }
+            }
+
             emit_agent_install_event(
                 emitter,
                 &task_id,
@@ -2813,6 +2838,23 @@ pub(crate) async fn acp_prepare_npx_agent_core(
             );
         }
         Err(e) => {
+            // When clean_first was true the uninstall step may already have
+            // succeeded by the time install failed, leaving the DB pointing at
+            // a version that no longer exists on disk. Resync the DB to the
+            // actual filesystem state so the UI doesn't mislead the user into
+            // thinking they can connect.
+            if clean_first {
+                let detected = detect_local_version(agent_type).await;
+                if let Err(sync_err) =
+                    agent_setting_service::set_installed_version(&db.conn, agent_type, detected)
+                        .await
+                {
+                    eprintln!(
+                        "[acp] failed to resync installed_version after clean upgrade failure: {sync_err}"
+                    );
+                }
+                emit_acp_agents_updated(emitter, "npx_prepare_failed", Some(agent_type));
+            }
             emit_agent_install_event(
                 emitter,
                 &task_id,
@@ -2829,12 +2871,21 @@ pub(crate) async fn acp_prepare_npx_agent_core(
 pub async fn acp_prepare_npx_agent(
     agent_type: AgentType,
     registry_version: Option<String>,
+    clean_first: Option<bool>,
     task_id: String,
     db: State<'_, AppDatabase>,
     app: tauri::AppHandle,
 ) -> Result<String, AcpError> {
     let emitter = EventEmitter::Tauri(app);
-    acp_prepare_npx_agent_core(agent_type, registry_version, task_id, &db, &emitter).await
+    acp_prepare_npx_agent_core(
+        agent_type,
+        registry_version,
+        clean_first.unwrap_or(false),
+        task_id,
+        &db,
+        &emitter,
+    )
+    .await
 }
 
 pub(crate) async fn acp_uninstall_agent_core(

src-tauri/src/web/handlers/acp.rs

@@ -492,6 +492,8 @@ pub async fn acp_detect_agent_local_version(
 pub struct AcpPrepareNpxAgentParams {
     pub agent_type: AgentType,
     pub registry_version: Option<String>,
+    #[serde(default)]
+    pub clean_first: bool,
     pub task_id: String,
 }
 
@@ -504,6 +506,7 @@ pub async fn acp_prepare_npx_agent(
     let result = acp_commands::acp_prepare_npx_agent_core(
         params.agent_type,
         params.registry_version,
+        params.clean_first,
         params.task_id,
         db,
         &emitter,