feat(ptc): run host tool calls on the outer runtime so delegation fans out

The program/PTC VM runs on a nested single-thread runtime, so parallel_task's
child agents couldn't actually run in parallel — delegation in a script was
broken (and was blocked in 4.2.3). Now execute_host_tool_json captures the
OUTER multi-threaded session runtime Handle and spawns the tool there, so
ctx.tool('parallel_task', …) fans out child agents in parallel. Re-allow
task/parallel_task in script_allowed_tools. Bumps to 4.2.6.

Author: RoyLin

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "a3s-code-core"
-version = "4.2.5"
+version = "4.2.6"
 edition = "2021"
 authors = ["A3S Lab Team"]
 license = "MIT"

core/Cargo.toml

@@ -213,12 +213,9 @@ fn script_allowed_tools(args: &serde_json::Value, registry: &ToolRegistry) -> Ha
         .unwrap_or_else(|| registry.list().into_iter().collect());
 
     allowed.remove("program");
-    // Delegation tools can't run inside a PTC script: child agents need the
-    // multi-threaded session runtime, but the script executes on a nested
-    // single-thread runtime where they can't fan out. Force the model to call
-    // them directly instead of `ctx.tool("parallel_task", ...)`.
-    allowed.remove("task");
-    allowed.remove("parallel_task");
+    // `task`/`parallel_task` ARE allowed in PTC scripts now: host tool calls run
+    // on the outer multi-threaded runtime (see execute_host_tool_json), so
+    // `ctx.tool("parallel_task", …)` fans out child agents in parallel.
     allowed
 }
 
@@ -277,6 +274,9 @@ async fn run_quickjs_script(
         .max_output_bytes
         .unwrap_or(DEFAULT_SCRIPT_MAX_OUTPUT_BYTES);
     let executable_source = script_source_with_host_entrypoint(source)?;
+    // Captured on the outer multi-threaded runtime (we're async here, before the
+    // VM's nested single-thread runtime is built) so host tool calls fan out.
+    let outer = tokio::runtime::Handle::current();
     let state = Arc::new(Mutex::new(ScriptVmState {
         registry,
         ctx,
@@ -285,6 +285,7 @@ async fn run_quickjs_script(
         max_output_bytes,
         tool_calls: 0,
         records: Vec::new(),
+        outer,
     }));
 
     let vm_state = Arc::clone(&state);
@@ -407,6 +408,10 @@ struct ScriptVmState {
     max_output_bytes: usize,
     tool_calls: usize,
     records: Vec<ScriptCallRecord>,
+    /// Handle to the OUTER multi-threaded session runtime. The script VM runs on
+    /// a nested single-thread runtime; host tool calls are dispatched here so
+    /// delegation tools (`parallel_task`/`task`) can actually fan out children.
+    outer: tokio::runtime::Handle,
 }
 
 fn embedded_script_bootstrap(inputs_json: &str) -> String {
@@ -447,7 +452,7 @@ async fn execute_host_tool_json(
     let args = serde_json::from_str(&args_json).map_err(|err| {
         JsError::new_from_js_message("string", "object", format!("invalid tool args JSON: {err}"))
     })?;
-    let (registry, ctx, max_output_bytes) = {
+    let (registry, ctx, max_output_bytes, outer) = {
         let mut script = state.lock().await;
         if !script.allowed_tools.contains(&tool) {
             return Err(JsError::new_from_js_message(
@@ -468,12 +473,22 @@ async fn execute_host_tool_json(
             Arc::clone(&script.registry),
             script.ctx.clone(),
             script.max_output_bytes,
+            script.outer.clone(),
         )
     };
 
-    let result = registry
-        .execute_with_context(&tool, &args, &ctx)
+    // Run the tool on the OUTER multi-threaded runtime (not this nested
+    // single-thread VM runtime) so delegation tools can spawn child agents that
+    // actually run in parallel — `ctx.tool("parallel_task", …)` now fans out.
+    let tool_for_spawn = tool.clone();
+    let result = outer
+        .spawn(async move {
+            registry
+                .execute_with_context(&tool_for_spawn, &args, &ctx)
+                .await
+        })
         .await
+        .map_err(|err| JsError::new_from_js_message("tool", "spawn", err.to_string()))?
         .map_err(|err| JsError::new_from_js_message("tool", "result", err.to_string()))?;
     let mut output = result.output;
     if output.len() > max_output_bytes {
@@ -676,6 +691,22 @@ mod tests {
         assert!(!allowed.contains("program"));
     }
 
+    #[test]
+    fn program_tool_allows_delegation_tools_in_scripts() {
+        // Delegation tools are allowed in PTC scripts again (host tool calls run
+        // on the outer multi-threaded runtime, so they fan out). Only `program`
+        // stays stripped (no nested PTC recursion).
+        let registry = ToolRegistry::new(PathBuf::from("/tmp"));
+        let args = serde_json::json!({
+            "allowed_tools": ["parallel_task", "task", "program", "echo"]
+        });
+        let allowed = script_allowed_tools(&args, &registry);
+        assert!(allowed.contains("parallel_task"));
+        assert!(allowed.contains("task"));
+        assert!(allowed.contains("echo"));
+        assert!(!allowed.contains("program"));
+    }
+
     #[tokio::test]
     async fn program_tool_source_uses_default_all_registered_tools() {
         let registry = Arc::new(ToolRegistry::new(PathBuf::from("/tmp")));

core/src/tools/program_tool.rs

@@ -1,6 +1,6 @@
 [package]
 name = "a3s-code-node"
-version = "4.2.5"
+version = "4.2.6"
 edition = "2021"
 authors = ["A3S Lab Team"]
 license = "MIT"
@@ -11,7 +11,7 @@ description = "A3S Code Node.js bindings - Native addon via napi-rs"
 crate-type = ["cdylib"]
 
 [dependencies]
-a3s-code-core = { version = "4.2.5", path = "../../core", features = ["ahp", "s3", "serve"] }
+a3s-code-core = { version = "4.2.6", path = "../../core", features = ["ahp", "s3", "serve"] }
 napi = { version = "2", features = ["async", "napi6", "serde-json"] }
 napi-derive = "2"
 tokio = { version = "1.35", features = ["full"] }

sdk/node/Cargo.toml

@@ -1,6 +1,6 @@
 {
   "name": "@a3s-lab/code",
-  "version": "4.2.5",
+  "version": "4.2.6",
   "description": "A3S Code - Native Node.js bindings for the coding-agent runtime",
   "main": "index.js",
   "types": "index.d.ts",
@@ -43,11 +43,11 @@
     "test:helpers": "node test-helpers.mjs"
   },
   "optionalDependencies": {
-    "@a3s-lab/code-darwin-arm64": "4.2.5",
-    "@a3s-lab/code-linux-x64-gnu": "4.2.5",
-    "@a3s-lab/code-linux-x64-musl": "4.2.5",
-    "@a3s-lab/code-linux-arm64-gnu": "4.2.5",
-    "@a3s-lab/code-linux-arm64-musl": "4.2.5",
-    "@a3s-lab/code-win32-x64-msvc": "4.2.5"
+    "@a3s-lab/code-darwin-arm64": "4.2.6",
+    "@a3s-lab/code-linux-x64-gnu": "4.2.6",
+    "@a3s-lab/code-linux-x64-musl": "4.2.6",
+    "@a3s-lab/code-linux-arm64-gnu": "4.2.6",
+    "@a3s-lab/code-linux-arm64-musl": "4.2.6",
+    "@a3s-lab/code-win32-x64-msvc": "4.2.6"
   }
 }

sdk/node/examples/package-lock.json

@@ -7,7 +7,7 @@ name = "a3s-code"
 # Keep in sync with crates/code core release. The bootstrap loader fetches
 # the matching native wheel from `https://github.com/AI45Lab/Code/releases/tag/v<version>`
 # at import time.
-version = "4.2.5"
+version = "4.2.6"
 description = "A3S Code Python SDK — pure-Python bootstrap that fetches the native wheel from GitHub Releases"
 readme = "README.md"
 license = {text = "MIT"}

sdk/node/package-lock.json

@@ -31,7 +31,7 @@
 
 # Version is the bootstrap's own version, which equals the matching native
 # wheel version on GH Releases. Bumped by the release workflow.
-__version__ = "4.2.5"
+__version__ = "4.2.6"
 
 _DEFAULT_BASE_URL = "https://github.com/AI45Lab/Code/releases/download"
 _REQUEST_TIMEOUT_S = 120

sdk/node/package.json

@@ -1,6 +1,6 @@
 [package]
 name = "a3s-code-py"
-version = "4.2.5"
+version = "4.2.6"
 edition = "2021"
 authors = ["A3S Lab Team"]
 license = "MIT"
@@ -12,7 +12,7 @@ name = "a3s_code"
 crate-type = ["cdylib"]
 
 [dependencies]
-a3s-code-core = { version = "4.2.5", path = "../../core", features = ["ahp", "s3", "serve"] }
+a3s-code-core = { version = "4.2.6", path = "../../core", features = ["ahp", "s3", "serve"] }
 pyo3 = "0.23"
 tokio = { version = "1.35", features = ["full"] }
 serde_json = "1.0"