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

pkg/config/config_test.go

@@ -441,3 +441,39 @@ providers:
 		t.Fatalf("err = %v", err)
 	}
 }
+
+func TestLoadDefaultsThinkingParamByAPIType(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("AGENTU_TEST_KEY", "sk-test")
+	path := filepath.Join(dir, "agentu.yaml")
+	if err := os.WriteFile(path, []byte(`
+providers:
+  chat:
+    api_type: chat
+    base_url: https://chat.example.com
+    api_key: ${AGENTU_TEST_KEY}
+    models:
+      - id: chat-model
+        thinking: none
+  responses:
+    api_type: responses
+    base_url: https://responses.example.com
+    api_key: ${AGENTU_TEST_KEY}
+    models:
+      - id: responses-model
+        thinking: high
+`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := cfg.Providers["chat"].ThinkingParam; got != "thinking" {
+		t.Fatalf("chat thinking param = %q, want %q", got, "thinking")
+	}
+	if got := cfg.Providers["responses"].ThinkingParam; got != "reasoning" {
+		t.Fatalf("responses thinking param = %q, want %q", got, "reasoning")
+	}
+}