fix: persist /model selection across restarts (#707)

* fix: persist /model selection across restarts

The /model command called set_model() on the LLM provider but never
saved the choice to settings, so the model reverted on restart. Now
persists to both the DB settings store and config.toml.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address CI clippy lint and use spawn_blocking for TOML I/O

- Use struct init syntax instead of field reassignment in test (clippy)
- Wrap sync filesystem operations in spawn_blocking to avoid blocking
  the tokio executor

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* style: fix rustfmt formatting

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address review feedback — handle JoinError, remove exists() guard

- Log warning if spawn_blocking task panics/is cancelled (JoinError)
- Remove toml_path.exists() guard; load_toml already returns Ok(None)
  for missing files, so permission errors are no longer silently skipped

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/agent/commands.rs

@@ -663,10 +663,14 @@ impl Agent {
                     }
 
                     match self.llm().set_model(requested) {
-                        Ok(()) => Ok(SubmissionResult::response(format!(
-                            "Switched model to: {}",
-                            requested
-                        ))),
+                        Ok(()) => {
+                            // Persist the model choice so it survives restarts.
+                            self.persist_selected_model(requested).await;
+                            Ok(SubmissionResult::response(format!(
+                                "Switched model to: {}",
+                                requested
+                            )))
+                        }
                         Err(e) => Ok(SubmissionResult::error(format!(
                             "Failed to switch model: {}",
                             e
@@ -822,4 +826,42 @@ impl Agent {
             _ => Ok(None),
         }
     }
+
+    /// Persist the selected model to the settings store (DB and/or TOML config).
+    ///
+    /// Best-effort: logs warnings on failure but does not propagate errors,
+    /// since the in-memory model switch already succeeded.
+    async fn persist_selected_model(&self, model: &str) {
+        // 1. Persist to DB if available.
+        if let Some(store) = self.store() {
+            let value = serde_json::Value::String(model.to_string());
+            if let Err(e) = store.set_setting("default", "selected_model", &value).await {
+                tracing::warn!("Failed to persist model to DB: {}", e);
+            }
+        }
+
+        // 2. Update TOML config file if it exists (sync I/O in spawn_blocking).
+        let model_owned = model.to_string();
+        if let Err(e) = tokio::task::spawn_blocking(move || {
+            let toml_path = crate::settings::Settings::default_toml_path();
+            match crate::settings::Settings::load_toml(&toml_path) {
+                Ok(Some(mut settings)) => {
+                    settings.selected_model = Some(model_owned);
+                    if let Err(e) = settings.save_toml(&toml_path) {
+                        tracing::warn!("Failed to persist model to config.toml: {}", e);
+                    }
+                }
+                Ok(None) => {
+                    // No config file on disk; nothing to update.
+                }
+                Err(e) => {
+                    tracing::warn!("Failed to load config.toml for model persistence: {}", e);
+                }
+            }
+        })
+        .await
+        {
+            tracing::warn!("Model TOML persistence task failed: {}", e);
+        }
+    }
 }

src/settings.rs

@@ -1198,6 +1198,31 @@ mod tests {
         assert_eq!(loaded.heartbeat.interval_secs, 900);
     }
 
+    /// Regression test: /model command must persist selected_model to TOML config.
+    /// Prior to the fix, `set_model()` only changed the in-memory provider and the
+    /// choice was lost on restart.
+    #[test]
+    fn toml_selected_model_update_persists() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+
+        // Start with a config that has a different model.
+        let settings = Settings {
+            selected_model: Some("old-model".to_string()),
+            ..Default::default()
+        };
+        settings.save_toml(&path).unwrap();
+
+        // Simulate what persist_selected_model does: load, update, save.
+        let mut loaded = Settings::load_toml(&path).unwrap().unwrap();
+        loaded.selected_model = Some("new-model".to_string());
+        loaded.save_toml(&path).unwrap();
+
+        // Verify the change survived a reload.
+        let reloaded = Settings::load_toml(&path).unwrap().unwrap();
+        assert_eq!(reloaded.selected_model, Some("new-model".to_string()));
+    }
+
     #[test]
     fn toml_missing_file_returns_none() {
         let result = Settings::load_toml(std::path::Path::new("/tmp/nonexistent_config.toml"));