fix(runtime): add check for unconfigured provider to prevent misleading API errors

src/app/runtime/actions/mod.rs

@@ -725,6 +725,23 @@ fn spawn_turn(state: &AppStateRest) {
         .find(|role| role.provider == state.settings.provider && role.model == state.settings.model)
         .and_then(|role| role.context_window)
         .unwrap_or(state.app_config.default_context_window) as usize;
+    // The selected provider has no entry in app_config at all (e.g. the
+    // Claude-settings auto-detection that registers "claude" found nothing
+    // this run). Without this check, LlmClient::new silently falls back to
+    // the zen default base URL while keeping this provider's model name —
+    // a mismatched request that reaches a real server and comes back as a
+    // confusing "Missing API key" 401 from an unrelated provider, instead
+    // of the actual problem: the configured provider doesn't exist.
+    if base_url.is_none() {
+        if let Ok(mut q) = state.turn_events.lock() {
+            q.push_back(TurnEvent::Error(format!(
+                "Provider '{}' is not configured — no matching entry found. \
+                 Pick a different provider in Settings, or configure it.",
+                state.settings.provider
+            )));
+        }
+        return;
+    }
     if api_key.is_empty() {
         if let Some(provider_cfg) = state.app_config.providers.get(&state.settings.provider) {
             api_key = provider_cfg.api_key_env.as_ref()