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.

agent/src/llm.rs

@@ -3,6 +3,7 @@
 //! The conversation is stored in a neutral format, so the agent can switch
 //! between the three shapes.
 
+use sausage_plugin::schema;
 use serde::{Deserialize, Serialize};
 use serde_json::{Value, json};
 #[cfg(target_os = "wasi")]
@@ -22,17 +23,50 @@ pub struct Config {
     pub token: String,
     /// Permit an empty token and omit authentication headers.
     pub allow_no_token: bool,
-    /// Optional reasoning effort for OpenAI models only (wins over `thinking` there).
-    #[serde(default)]
-    pub reasoning_effort: Option<String>,
     /// An optional cap on generated tokens.
     #[serde(default)]
     pub max_tokens: Option<u32>,
-    /// Thinking effort for all APIs: "low", "medium", "high", "xhigh", "max" (`LEVELS`), or "off"/unset for none.
-    /// Anthropic: adaptive thinking + output_config.effort; OpenAI: reasoning.effort. A level the model rejects is
-    /// replaced by the nearest accepted one (logged), never by "off".
+    /// The thinking level of each turn. Unset: the model's default.
     #[serde(default)]
-    pub thinking: Option<String>,
+    pub thinking: Option<Thinking>,
+}
+
+/// How much the model thinks before it answers.
+///
+/// OpenAI Responses gets `reasoning.effort`, Chat Completions gets `reasoning_effort`, and Anthropic
+/// gets adaptive thinking with `output_config.effort`. If the model rejects a level, the agent uses
+/// the nearest level that the model accepts, never `off`.
+#[schema]
+#[derive(Clone, Copy, PartialEq, Debug)]
+#[serde(rename_all = "lowercase")]
+pub enum Thinking {
+    /// No thinking: OpenAI gets the effort `none`, and Anthropic gets disabled thinking. If an
+    /// OpenAI model cannot switch thinking off, the agent uses `low`.
+    Off,
+    /// The least thinking.
+    Low,
+    /// Moderate thinking.
+    Medium,
+    /// Much thinking.
+    High,
+    /// More thinking than `high`, where the model supports it.
+    Xhigh,
+    /// The most thinking that the model supports.
+    Max,
+}
+
+impl Thinking {
+    /// The effort that an OpenAI request carries: `none`, or one of `LEVELS`.
+    fn effort(self) -> &'static str {
+        match self {
+            Thinking::Off => "none",
+            Thinking::Low => "low",
+            Thinking::Medium => "medium",
+            Thinking::High => "high",
+            Thinking::Xhigh => "xhigh",
+            Thinking::Max => "max",
+        }
+    }
 }
 
 impl Config {
@@ -98,7 +132,11 @@ fn fallback_effort(want: &str, error: &str, tried: &[String]) -> Option<String>
     } else {
         LEVELS.to_vec()
     };
-    let at = LEVELS.iter().position(|l| *l == want).unwrap_or(1) as i32;
+    // `none` is below all levels, so its nearest level is `low`.
+    let at = LEVELS
+        .iter()
+        .position(|l| *l == want)
+        .map_or(-1, |i| i as i32);
     pool.into_iter()
         .filter(|l| *l != want && !tried.iter().any(|t| t == l))
         .min_by_key(|l| {
@@ -130,6 +168,22 @@ mod tests {
         }
         let cfg = Config::parse(b"api: openai-chat-completions\nbase_url: http://localhost/v1\nmodel: local\ntoken: ''\nallow_no_token: true").unwrap();
         assert!(cfg.bearer().is_empty());
+        assert_eq!(cfg.thinking, None);
+    }
+
+    #[test]
+    fn thinking_levels() {
+        use super::{Config, LEVELS, Thinking};
+        let base = "api: openai-responses\nbase_url: url\nmodel: model\ntoken: key\nthinking: ";
+        let parse = |level: &str| Config::parse(format!("{base}{level}").as_bytes());
+        assert_eq!(parse("off").unwrap().thinking, Some(Thinking::Off));
+        assert_eq!(Thinking::Off.effort(), "none");
+        for level in LEVELS {
+            assert_eq!(parse(level).unwrap().thinking.unwrap().effort(), level);
+        }
+        let error = parse("hihg").err().unwrap();
+        assert!(error.contains("/config/agent.yaml"), "{error}");
+        assert!(error.contains("thinking"), "{error}");
     }
 
     #[test]
@@ -178,10 +232,16 @@ mod tests {
             fallback_effort("xhigh", anthropic, &["xhigh".into()]).as_deref(),
             Some("high")
         );
-        let openai = "HTTP 400: Invalid value: 'ultra'. Supported values are: 'none', 'minimal', 'low', 'medium', 'high', 'xhigh', and 'max'.";
+        let openai = "HTTP 400: Invalid value: 'max'. Supported values are: 'none', 'minimal', 'low', 'medium', and 'high'.";
         assert_eq!(
-            fallback_effort("ultra", openai, &["ultra".into()]).as_deref(),
-            Some("medium")
+            fallback_effort("max", openai, &["max".into()]).as_deref(),
+            Some("high")
+        );
+        // A thinking-only model rejects `none`: use the lowest level.
+        let glm = "HTTP 400: GLM-5.3 is a thinking-only model; disabling thinking (reasoning_effort='none') is not supported.";
+        assert_eq!(
+            fallback_effort("none", glm, &["none".into()]).as_deref(),
+            Some("low")
         );
         // No list in the error: step to the neighbour, never to off.
         assert_eq!(
@@ -254,31 +314,14 @@ pub async fn complete(
     tools: &[Tool],
     history: &[Entry],
 ) -> Result<Vec<Entry>, String> {
-    let want = match cfg.api.as_str() {
-        "openai-responses" | "openai-chat-completions" => cfg
-            .reasoning_effort
-            .clone()
-            .or_else(|| cfg.thinking.clone()),
-        _ => cfg.thinking.clone(),
-    }
-    .filter(|t| t != "off");
+    let want = cfg.thinking.map(|level| level.effort().to_string());
     let mut effort = want.clone();
     let mut tried = Vec::new();
     loop {
         let result = match cfg.api.as_str() {
             "openai-responses" => openai(cfg, system, tools, history, effort.as_deref()).await,
             "openai-chat-completions" => chat(cfg, system, tools, history, effort.as_deref()).await,
-            "anthropic-messages" => {
-                anthropic(
-                    cfg,
-                    system,
-                    tools,
-                    history,
-                    want.is_some(),
-                    effort.as_deref(),
-                )
-                .await
-            }
+            "anthropic-messages" => anthropic(cfg, system, tools, history, effort.as_deref()).await,
             other => return Err(format!("unknown API shape {other:?}")),
         };
         match (result, effort.clone()) {
@@ -430,9 +473,9 @@ async fn anthropic(
     system: &str,
     tools: &[Tool],
     history: &[Entry],
-    thinking: bool,
     effort: Option<&str>,
 ) -> Result<Vec<Entry>, String> {
+    let disabled = cfg.thinking == Some(Thinking::Off);
     // Merge consecutive blocks of the same role into one message.
     let mut messages: Vec<(String, Vec<Value>)> = Vec::new();
     let mut push = |role: &str, block: Value| match messages.last_mut() {
@@ -462,7 +505,7 @@ async fn anthropic(
             ),
             // Thinking blocks go back unchanged (with their signature): required next to tool use.
             Entry::Opaque { api, model, item }
-                if api == "anthropic-messages" && model == &cfg.model && thinking =>
+                if api == "anthropic-messages" && model == &cfg.model && !disabled =>
             {
                 push("assistant", item.clone())
             }
@@ -486,10 +529,15 @@ async fn anthropic(
         "tools": tools,
         "max_tokens": cfg.max_tokens.unwrap_or(32000),
     });
-    if thinking {
-        body["thinking"] = json!({"type": "adaptive"});
-        if let Some(effort) = effort {
-            body["output_config"] = json!({"effort": effort});
+    // Unset: the model's default. Newer models think by default.
+    match cfg.thinking {
+        None => {}
+        Some(Thinking::Off) => body["thinking"] = json!({"type": "disabled"}),
+        Some(_) => {
+            body["thinking"] = json!({"type": "adaptive"});
+            if let Some(effort) = effort {
+                body["output_config"] = json!({"effort": effort});
+            }
         }
     }
     let url = format!("{}/v1/messages", cfg.base_url.trim_end_matches('/'));