agent: a thinking level in agent.yaml and per call

- thinking (off, low, medium, high, xhigh, max) is an enum: serde rejects
  unknown levels in the config, and the schema of agent.chat lists them.
  reasoning_effort, a second name for the same setting, is gone.
- agent.chat takes an optional thinking level for one turn.
- off really switches thinking off: OpenAI gets the effort none, and
  Anthropic gets disabled thinking (newer Claude models think by
  default). A model that cannot switch thinking off gets low.
- Unset means the model's default. Anthropic thinking blocks now return
  unless thinking is off, because newer models think by default.
- The template sets thinking: medium and shows it in each example, with
  current model names.
- Checked against the proxy with gpt-6-luna, glm-5.3-flash, and
  claude-haiku-5-5.

cli/tests/host/agent.rs

@@ -241,6 +241,10 @@ async fn unconfigured_chat_names_the_configuration() {
             "api: openai-responses\nbase_url: http://localhost/v1\nmodel: test\ntoken: CHANGE_ME",
             "token",
         ),
+        (
+            "api: openai-responses\nbase_url: http://localhost/v1\nmodel: test\ntoken: key\nthinking: hihg",
+            "thinking",
+        ),
     ] {
         std::fs::write(&path, config).unwrap();
         let error = host
@@ -507,11 +511,7 @@ async fn private_items_are_scoped_to_the_model() {
     for api in [APIS[0], APIS[1]] {
         let mut server = Llm::new(api).await;
         let world = TestWorld::new(&server);
-        let config_path = world.0.join("config/agent.yaml");
-        let mut config: Value =
-            serde_yaml_ng::from_slice(&std::fs::read(&config_path).unwrap()).unwrap();
-        config["thinking"] = json!("high");
-        std::fs::write(config_path, serde_yaml_ng::to_string(&config).unwrap()).unwrap();
+        // Without a thinking level, newer models think by default, so their items return.
         std::fs::create_dir_all(world.0.join("state/agent")).unwrap();
         let mut entries = vec![json!({"kind":"user","text":"old turn"})];
         for (model, marker) in [
@@ -546,6 +546,60 @@ async fn private_items_are_scoped_to_the_model() {
     }
 }
 
+/// Each API gets the configured thinking level. A level in the call applies to that turn only.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn thinking_levels_reach_each_api() {
+    for api in APIS {
+        let mut server = Llm::new(api).await;
+        let world = TestWorld::new(&server);
+        let config_path = world.0.join("config/agent.yaml");
+        let mut config: Value =
+            serde_yaml_ng::from_slice(&std::fs::read(&config_path).unwrap()).unwrap();
+        config["thinking"] = json!("high");
+        std::fs::write(config_path, serde_yaml_ng::to_string(&config).unwrap()).unwrap();
+        let host = world.start().await;
+        // Off is `none` for OpenAI, and disabled thinking without an effort for Anthropic.
+        let off = if api == APIS[1] { None } else { Some("none") };
+        for (thinking, effort) in [
+            (None, Some("high")),
+            (Some("low"), Some("low")),
+            (Some("off"), off),
+            (None, Some("high")),
+        ] {
+            let mut params = json!({"text":"hello"});
+            if let Some(thinking) = thinking {
+                params["thinking"] = json!(thinking);
+            }
+            let caller = host.clone();
+            let turn =
+                tokio::spawn(async move { caller.call("agent.chat", params).await.unwrap() });
+            let (body, reply) = server.next().await;
+            let sent = if api == APIS[0] {
+                &body["reasoning"]["effort"]
+            } else if api == APIS[2] {
+                &body["reasoning_effort"]
+            } else {
+                let mode = if thinking == Some("off") {
+                    "disabled"
+                } else {
+                    "adaptive"
+                };
+                assert_eq!(body["thinking"]["type"], mode, "{body}");
+                &body["output_config"]["effort"]
+            };
+            assert_eq!(sent.as_str(), effort, "{api} {thinking:?}");
+            reply.send((200, server.answer("done", &[]))).unwrap();
+            assert_eq!(turn.await.unwrap(), "done");
+        }
+        let error = host
+            .call("agent.chat", json!({"text":"hello","thinking":"hihg"}))
+            .await
+            .unwrap_err();
+        assert_eq!(error["code"], -32602, "{error}");
+        host.stop().await;
+    }
+}
+
 /// Separate assistant messages retain a separator in the final answer.
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn final_texts_have_a_separator() {