feat(session,llm): restore session runtime on resume; align Responses API details

internal/session/manager.go

@@ -68,11 +68,29 @@ func (m *Manager) Resume(id string) error {
 		return err
 	}
 	m.currentSession = sess
+	m.restoreRuntime(sess)
 	m.agent.SetMessages(sess.Messages)
 	m.agent.SetLastUsage(sess.LastUsage)
 	return nil
 }
 
+// restoreRuntime switches the manager and agent back to the provider, model,
+// and thinking level recorded on a resumed session. Values that are no longer
+// valid for the current config are skipped and the defaults remain active.
+func (m *Manager) restoreRuntime(sess *Session) {
+	if sess.Provider != "" && sess.Provider != m.providerName {
+		if _, ok := m.cfg.Providers[sess.Provider]; ok {
+			_, _ = m.SetProvider(sess.Provider)
+		}
+	}
+	if sess.Model != "" && sess.Model != m.provider.Model {
+		_, _ = m.SetModel(sess.Model)
+	}
+	if sess.Thinking != "" && sess.Thinking != m.provider.Thinking {
+		_, _ = m.SetThinking(sess.Thinking)
+	}
+}
+
 // Save persists the current session to disk.
 func (m *Manager) Save() error {
 	if m.store == nil || m.currentSession == nil {
@@ -82,6 +100,8 @@ func (m *Manager) Save() error {
 	m.currentSession.LastUsage = m.agent.LastUsage()
 	m.currentSession.Provider = m.providerName
 	m.currentSession.Model = m.provider.Model
+	m.currentSession.APIType = m.provider.APIType
+	m.currentSession.Thinking = m.provider.Thinking
 	// Auto-name if empty
 	if m.currentSession.Name == "" {
 		m.currentSession.Name = DefaultName(m.currentSession.Messages)
@@ -150,6 +170,8 @@ func (m *Manager) NewSession() (string, error) {
 			m.currentSession.Messages = msgs
 			m.currentSession.Provider = m.providerName
 			m.currentSession.Model = m.provider.Model
+			m.currentSession.APIType = m.provider.APIType
+			m.currentSession.Thinking = m.provider.Thinking
 			if m.currentSession.Name == "" {
 				m.currentSession.Name = DefaultName(msgs)
 			}
@@ -257,7 +279,7 @@ func (m *Manager) SetThinking(level string) (string, error) {
 	m.provider.Thinking = level
 	m.provider.ThinkingConfigured = true
 	if m.provider.ThinkingParam == "" {
-		m.provider.ThinkingParam = "thinking"
+		m.provider.ThinkingParam = config.DefaultThinkingParam(m.provider.APIType)
 	}
 	m.cfg.Providers[m.providerName] = m.provider
 	m.syncAgent(nil)