feat: per-agent model selection, shell custom name, and json_candidates export

- Sub-agents and call-agents now use configured model from models map
  when available, falling back to parent model
- Add CompletionRunner::reserve_chat_history() builder method
- Export json_candidates() as public utility for parsing model JSON output
- Allow ShellTool to accept a custom name for multi-instance scenarios
- Bump anda_engine to 0.11.31

Co-Authored-By: Anda Bot <noreply@anda.bot>

Author: zensh

anda_engine/Cargo.toml

@@ -3,7 +3,7 @@ name = "anda_engine"
 description = "Agents engine for Anda -- an AI agent framework built with Rust, powered by ICP and TEEs."
 repository = "https://github.com/ldclabs/anda/tree/main/anda_engine"
 publish = true
-version = "0.11.30"
+version = "0.11.31"
 edition.workspace = true
 keywords.workspace = true
 categories.workspace = true

anda_engine/src/context/agent.rs

@@ -120,7 +120,10 @@ impl AgentCtx {
                 .child(format!("A:{}", agent_name.to_ascii_lowercase()))?,
             label: agent_label.to_string(),
             root: self.root.clone(),
-            model: self.model.clone(),
+            model: self
+                .models
+                .get(agent_label)
+                .unwrap_or_else(|| self.model.clone()),
             models: self.models.clone(),
             tools: self.tools.clone(),
             agents: self.agents.clone(),
@@ -159,7 +162,10 @@ impl AgentCtx {
             )?,
             label: agent_label.to_string(),
             root: self.root.clone(),
-            model: self.model.clone(),
+            model: self
+                .models
+                .get(agent_label)
+                .unwrap_or_else(|| self.model.clone()),
             models: self.models.clone(),
             tools: self.tools.clone(),
             agents: self.agents.clone(),
@@ -1000,6 +1006,14 @@ impl CompletionRunner {
         }
     }
 
+    /// Reserves the chat history for the completion runner.
+    pub fn reserve_chat_history(self, chat_history: Vec<Message>) -> Self {
+        Self {
+            chat_history,
+            ..self
+        }
+    }
+
     /// Returns whether the completion has finished.
     pub fn is_done(&self) -> bool {
         self.done

anda_engine/src/context/tool.rs

@@ -405,7 +405,7 @@ async fn select_requested_names_with_model(
 }
 
 fn parse_selector_tool_names(content: &str) -> Vec<String> {
-    for candidate in selector_json_candidates(content) {
+    for candidate in json_candidates(content) {
         if let Ok(output) = serde_json::from_str::<ToolsSelectNamesOutput>(&candidate) {
             return output.tools;
         }
@@ -417,7 +417,8 @@ fn parse_selector_tool_names(content: &str) -> Vec<String> {
     Vec::new()
 }
 
-fn selector_json_candidates(content: &str) -> Vec<String> {
+/// Extracts JSON candidates from the input string by applying various heuristics, such as stripping markdown code blocks and extracting JSON-like substrings. This increases the chances of successfully parsing the model output even when it is not perfectly formatted.
+pub fn json_candidates(content: &str) -> Vec<String> {
     let mut candidates = Vec::new();
     let mut seen = BTreeSet::new();
 

anda_engine/src/extension/shell.rs

@@ -223,6 +223,7 @@ pub type ShellToolHook = DynToolHook<ExecArgs, ExecOutput>;
 pub struct ShellTool {
     runtime: Arc<dyn Executor>,
     envs: HashMap<String, String>,
+    name: String,
     description: String,
 }
 
@@ -235,7 +236,12 @@ impl ShellTool {
     /// The environment map is not forwarded wholesale. Agents must request
     /// specific keys through [`ExecArgs::env_keys`], and invalid environment
     /// variable names are ignored.
-    pub fn new(runtime: Arc<dyn Executor>, envs: HashMap<String, String>) -> Self {
+    pub fn new(
+        runtime: Arc<dyn Executor>,
+        envs: HashMap<String, String>,
+        name: Option<String>,
+    ) -> Self {
+        let name = name.unwrap_or_else(|| Self::NAME.to_string());
         let description = format!(
             "Execute a shell command in the workspace directory (Runtime: {}, OS: {}, Shell: {})",
             runtime.name(),
@@ -246,6 +252,7 @@ impl ShellTool {
         Self {
             runtime,
             envs,
+            name,
             description,
         }
     }
@@ -291,7 +298,7 @@ impl Tool<BaseCtx> for ShellTool {
     type Output = ExecOutput;
 
     fn name(&self) -> String {
-        Self::NAME.to_string()
+        self.name.clone()
     }
 
     fn description(&self) -> String {
@@ -676,7 +683,7 @@ mod tests {
         let mut envs = HashMap::new();
         envs.insert("ANDA_TEST_ENV".to_string(), "configured".to_string());
         envs.insert("INVALID-NAME".to_string(), "ignored".to_string());
-        let tool = ShellTool::new(Arc::new(TestRuntime::new("sandbox")), envs);
+        let tool = ShellTool::new(Arc::new(TestRuntime::new("sandbox")), envs, None);
 
         let collected = tool.collect_shell_env_vars(&[
             " ANDA_TEST_ENV ".to_string(),