feat: Full support for map node types

src/config/request_context.rs

@@ -172,7 +172,6 @@ impl RequestContext {
     /// - `auto_continue_count` reset to 0 (each branch starts a fresh
     ///   continuation budget)
     /// - `last_continuation_response` reset to None
-    #[allow(dead_code)]
     pub fn fork_for_branch(&self) -> Self {
         Self {
             app: Arc::clone(&self.app),

src/graph/executor.rs

@@ -1,6 +1,7 @@
 use super::agent::AgentNodeExecutor;
 use super::llm::LlmNodeExecutor;
 use super::logging::GraphLogger;
+use super::map::MapNodeExecutor;
 use super::rag::RagNodeExecutor;
 use super::script::ScriptExecutor;
 use super::staging::BranchWrites;
@@ -74,6 +75,10 @@ impl GraphExecutor {
         let max_iterations = graph.settings.max_loop_iterations;
         let graph_timeout = graph.settings.timeout.map(Duration::from_secs);
         let max_concurrency = graph.settings.max_concurrency;
+        // Wrap in Arc so spawned branch tasks can cheaply share the Graph for
+        // node lookup (especially the map executor, which needs to resolve its
+        // `branch:` target from inside a spawned task).
+        let graph = Arc::new(graph);
         let start = Instant::now();
 
         let mut frontier: HashSet<String> = HashSet::from([graph.start.clone()]);
@@ -150,7 +155,7 @@ impl GraphExecutor {
                 let branch_state = state.fork_for_branch_state();
                 let branch_ctx = ctx.fork_for_branch();
                 let script_exec_clone = script_executor.clone();
-                let graph_name = graph.name.clone();
+                let graph_clone = Arc::clone(&graph);
                 let current = node_id.clone();
                 let sem_clone = semaphore.clone();
                 let abort_clone = abort_signal.clone();
@@ -171,15 +176,13 @@ impl GraphExecutor {
                     let node_start = Instant::now();
                     let mut state = branch_state;
                     let mut ctx = branch_ctx;
-                    let result = step(
-                        &node,
-                        &mut state,
-                        &mut ctx,
-                        &script_exec_clone,
-                        &graph_name,
-                        &current,
-                    )
-                    .await;
+                    let step_ctx = StepContext {
+                        graph: graph_clone.as_ref(),
+                        script_executor: &script_exec_clone,
+                        max_concurrency,
+                        abort_signal: &abort_clone,
+                    };
+                    let result = step(&node, &mut state, &mut ctx, &step_ctx, &current).await;
                     let elapsed = node_start.elapsed();
                     (current, state, result, elapsed)
                 });
@@ -263,6 +266,23 @@ fn sorted_frontier(frontier: &HashSet<String>) -> Vec<String> {
     v
 }
 
+// Bundles the engine-config refs that every `step()` call needs to thread
+// through. Constructed once per spawned branch task (or once at the call site
+// for sequential paths) so step() and downstream executors (MapNodeExecutor)
+// take one parameter instead of five.
+pub(super) struct StepContext<'a> {
+    pub graph: &'a Graph,
+    pub script_executor: &'a ScriptExecutor,
+    pub max_concurrency: usize,
+    pub abort_signal: &'a AbortSignal,
+}
+
+impl StepContext<'_> {
+    pub fn graph_name(&self) -> &str {
+        &self.graph.name
+    }
+}
+
 enum StepResult {
     Continue(String),
     End(String),
@@ -272,8 +292,7 @@ async fn step(
     node: &Node,
     state: &mut StateManager,
     ctx: &mut RequestContext,
-    script_executor: &ScriptExecutor,
-    graph_name: &str,
+    step_ctx: &StepContext<'_>,
     current: &str,
 ) -> Result<StepResult> {
     match &node.node_type {
@@ -288,13 +307,16 @@ async fn step(
             Ok(StepResult::Continue(next))
         }
         NodeType::Script(script_node) => {
-            let dynamic = match script_executor.execute(script_node, state).await {
+            let dynamic = match step_ctx.script_executor.execute(script_node, state).await {
                 Ok(n) => n,
                 Err(e) => {
                     if let Some(fallback) = &script_node.fallback {
                         warn!(
                             "[graph:{}] script '{}' failed, routing to fallback '{}': {}",
-                            graph_name, current, fallback, e
+                            step_ctx.graph_name(),
+                            current,
+                            fallback,
+                            e
                         );
                         return Ok(StepResult::Continue(fallback.clone()));
                     }
@@ -334,10 +356,16 @@ async fn step(
             Ok(StepResult::Continue(next))
         }
         NodeType::End(end_node) => Ok(StepResult::End(resolve_end_output(end_node, state))),
-        NodeType::Map(_) => bail!(
-            "Map nodes are not yet supported in this build \
-             (parallel branch execution lands in Phase D/E)."
-        ),
+        NodeType::Map(map_node) => {
+            let next = node
+                .next_single()?
+                .ok_or_else(|| {
+                    anyhow!("map node '{current}' has no `next` and is not an end node")
+                })?
+                .to_string();
+            MapNodeExecutor::execute(map_node, state, ctx, step_ctx, current).await?;
+            Ok(StepResult::Continue(next))
+        }
     }
 }
 

src/graph/map.rs

@@ -0,0 +1,169 @@
+use super::agent::AgentNodeExecutor;
+use super::executor::StepContext;
+use super::llm::LlmNodeExecutor;
+use super::rag::RagNodeExecutor;
+use super::state::StateManager;
+use super::types::{MapNode, NodeType};
+use crate::config::RequestContext;
+use anyhow::{Context, Result, anyhow};
+use futures_util::future::join_all;
+use serde_json::Value;
+use std::collections::HashMap;
+use std::sync::Arc;
+use tokio::sync::Semaphore;
+use crate::graph::type_name;
+
+// Map sub-branches are atomic — the branch node has no `next` (enforced by
+// validator rule C.5). But LLM/RAG node executors require an `Option<&str>` for
+// their routing argument and error if it's `None`. Passing this sentinel
+// satisfies their contract; the map executor discards the returned routing.
+const MAP_BRANCH_SENTINEL_NEXT: &str = "__map_branch_continuation__";
+
+pub(super) struct MapNodeExecutor;
+
+impl MapNodeExecutor {
+    pub(super) async fn execute(
+        node: &MapNode,
+        state: &mut StateManager,
+        ctx: &mut RequestContext,
+        step_ctx: &StepContext<'_>,
+        node_id: &str,
+    ) -> Result<()> {
+        let over_value = state
+            .interpolate_raw(&node.over)
+            .with_context(|| format!("map node '{node_id}': evaluating `over` template"))?;
+
+        let items = over_value.as_array().ok_or_else(|| {
+            anyhow!(
+                "map node '{}': `over` template '{}' must resolve to an array, got {}",
+                node_id,
+                node.over,
+                type_name(&over_value)
+            )
+        })?;
+        let items = items.clone();
+
+        let branch_node = step_ctx
+            .graph
+            .get_node(&node.branch)
+            .ok_or_else(|| {
+                anyhow!(
+                    "map node '{node_id}': branch '{}' not found in graph",
+                    node.branch
+                )
+            })?
+            .clone();
+
+        let max_conc = node
+            .max_concurrency
+            .unwrap_or(step_ctx.max_concurrency)
+            .max(1);
+        let semaphore = Arc::new(Semaphore::new(max_conc));
+        let mut sub_tasks = Vec::with_capacity(items.len());
+
+        for (idx, item) in items.iter().enumerate() {
+            let item = item.clone();
+            let as_name = node.as_name.clone();
+            let branch_clone = branch_node.clone();
+            let mut sub_state = state.fork_for_branch_state();
+            let sub_ctx = ctx.fork_for_branch();
+            let script_clone = step_ctx.script_executor.clone();
+            let sub_branch_id = node.branch.clone();
+            let sem = semaphore.clone();
+            let abort = step_ctx.abort_signal.clone();
+
+            sub_state.state_mut().set(as_name, item);
+
+            let task = tokio::spawn(async move {
+                let _permit = sem
+                    .acquire()
+                    .await
+                    .expect("map semaphore should not be closed");
+                if abort.aborted() {
+                    return (
+                        idx,
+                        sub_state,
+                        Err(anyhow!("map sub-branch [{idx}] aborted")),
+                    );
+                }
+                let mut state = sub_state;
+                let mut ctx = sub_ctx;
+
+                let exec_result: Result<()> = match &branch_clone.node_type {
+                    NodeType::Llm(n) => LlmNodeExecutor::execute(
+                        n,
+                        Some(MAP_BRANCH_SENTINEL_NEXT),
+                        &mut state,
+                        &mut ctx,
+                    )
+                    .await
+                    .map(|_| ()),
+                    NodeType::Agent(n) => AgentNodeExecutor::execute(n, &mut state, &mut ctx)
+                        .await
+                        .map(|_| ()),
+                    NodeType::Rag(n) => RagNodeExecutor::execute(
+                        n,
+                        &sub_branch_id,
+                        Some(MAP_BRANCH_SENTINEL_NEXT),
+                        &mut state,
+                        &mut ctx,
+                    )
+                    .await
+                    .map(|_| ()),
+                    NodeType::Script(n) => script_clone.execute(n, &mut state).await.map(|_| ()),
+                    _ => Err(anyhow!(
+                        "map branch '{}' has type that cannot run inside a map \
+                         (validator should have caught this; internal error)",
+                        branch_clone.id
+                    )),
+                };
+
+                (idx, state, exec_result)
+            });
+            sub_tasks.push(task);
+        }
+
+        let joined = join_all(sub_tasks).await;
+
+        // Collect outputs keyed by input index so order is preserved regardless
+        // of finish order. This is the user-facing contract from plan E.2.
+        let mut outputs: HashMap<usize, Value> = HashMap::new();
+        for join_result in joined {
+            let (idx, sub_state, exec_result) =
+                join_result.map_err(|e| anyhow!("map sub-branch panicked: {e}"))?;
+
+            exec_result
+                .with_context(|| format!("map node '{node_id}': sub-branch [{idx}] failed"))?;
+
+            let output_value = sub_state
+                .state()
+                .get(&node.output_key)
+                .cloned()
+                .ok_or_else(|| {
+                    anyhow!(
+                        "map node '{node_id}': sub-branch [{idx}] did not write \
+                         `output_key` '{}'",
+                        node.output_key
+                    )
+                })?;
+
+            outputs.insert(idx, output_value);
+        }
+
+        let mut collected = Vec::with_capacity(items.len());
+        for idx in 0..items.len() {
+            let value = outputs.remove(&idx).ok_or_else(|| {
+                anyhow!(
+                    "map node '{node_id}': internal error: missing result for sub-branch [{idx}]"
+                )
+            })?;
+            collected.push(value);
+        }
+
+        state
+            .state_mut()
+            .set(node.collect_into.clone(), Value::Array(collected));
+
+        Ok(())
+    }
+}

src/graph/mod.rs

@@ -3,6 +3,7 @@ pub mod dispatch;
 pub mod executor;
 pub mod llm;
 pub mod logging;
+pub mod map;
 pub mod parser;
 pub mod rag;
 pub mod reducer;
@@ -14,6 +15,7 @@ pub mod types;
 pub mod user_interaction;
 pub mod validator;
 
+use serde_json::Value;
 pub use dispatch::{active_agent_graph_name, run_active_agent_graph};
 pub use executor::GraphExecutor;
 pub use parser::{GraphParser, agent_has_graph};
@@ -24,3 +26,14 @@ pub const GRAPH_SCHEMA_VERSION: &str = "1.0";
 pub const DEFAULT_MAX_LOOP_ITERATIONS: usize = 100;
 
 pub const MAX_STATE_SIZE_BYTES: usize = 32 * 1024;
+
+pub (in crate::graph) fn type_name(value: &Value) -> &'static str {
+	match value {
+		Value::Null => "null",
+		Value::Bool(_) => "bool",
+		Value::Number(_) => "number",
+		Value::String(_) => "string",
+		Value::Array(_) => "array",
+		Value::Object(_) => "object",
+	}
+}

src/graph/reducer.rs

@@ -1,6 +1,7 @@
 use super::types::Reducer;
 use anyhow::{Result, bail};
 use serde_json::{Number, Value};
+use crate::graph::type_name;
 
 /// Combines a branch's incoming write with the current state value (if any)
 /// via the specified reducer. The result is what gets written back to live
@@ -147,17 +148,6 @@ fn number_or_error(value: &Value, reducer_name: &str, position: &str) -> Result<
     }
 }
 
-fn type_name(value: &Value) -> &'static str {
-    match value {
-        Value::Null => "null",
-        Value::Bool(_) => "bool",
-        Value::Number(_) => "number",
-        Value::String(_) => "string",
-        Value::Array(_) => "array",
-        Value::Object(_) => "object",
-    }
-}
-
 // Numeric reducers compute in f64 for simplicity. We preserve integer typing
 // when the result is losslessly representable as i64 so `count: sum` stays an
 // integer rather than degrading to a float. Non-finite values (NaN, Inf) can't