feat(wfe-core): add step primitives for workflow control flow

12 step primitives implementing StepBody: DecideStep, IfStep, WhileStep,
ForEachStep, SequenceStep, DelayStep, WaitForStep, ScheduleStep,
RecurStep, PollEndpointStep, SagaContainerStep, EndStep.

Each primitive handles its state machine via persistence_data and
branch creation for container steps.

wfe-core/src/primitives/foreach_step.rs

@@ -0,0 +1,223 @@
+use async_trait::async_trait;
+use serde_json::json;
+
+use crate::models::ExecutionResult;
+use crate::traits::step::{StepBody, StepExecutionContext};
+
+/// A step that iterates over a collection, branching for each element.
+pub struct ForEachStep {
+    pub collection: Vec<serde_json::Value>,
+    pub run_parallel: bool,
+}
+
+impl Default for ForEachStep {
+    fn default() -> Self {
+        Self {
+            collection: Vec::new(),
+            run_parallel: true,
+        }
+    }
+}
+
+#[async_trait]
+impl StepBody for ForEachStep {
+    async fn run(&mut self, context: &StepExecutionContext<'_>) -> crate::Result<ExecutionResult> {
+        if self.collection.is_empty() {
+            return Ok(ExecutionResult::next());
+        }
+
+        if self.run_parallel {
+            // Parallel: branch with all collection values at once.
+            let children_active = context
+                .persistence_data
+                .and_then(|d| d.get("children_active"))
+                .and_then(|v| v.as_bool())
+                .unwrap_or(false);
+
+            if children_active {
+                let mut scope = context.execution_pointer.scope.clone();
+                scope.push(context.execution_pointer.id.clone());
+
+                if context.workflow.is_branch_complete(&scope) {
+                    Ok(ExecutionResult::next())
+                } else {
+                    Ok(ExecutionResult::persist(json!({"children_active": true})))
+                }
+            } else {
+                Ok(ExecutionResult::branch(
+                    self.collection.clone(),
+                    Some(json!({"children_active": true})),
+                ))
+            }
+        } else {
+            // Sequential: process one item at a time using current_index.
+            let current_index = context
+                .persistence_data
+                .and_then(|d| d.get("current_index"))
+                .and_then(|v| v.as_u64())
+                .unwrap_or(0) as usize;
+
+            let children_active = context
+                .persistence_data
+                .and_then(|d| d.get("children_active"))
+                .and_then(|v| v.as_bool())
+                .unwrap_or(false);
+
+            if children_active {
+                // Check if current child is complete.
+                let mut scope = context.execution_pointer.scope.clone();
+                scope.push(context.execution_pointer.id.clone());
+
+                if context.workflow.is_branch_complete(&scope) {
+                    let next_index = current_index + 1;
+                    if next_index >= self.collection.len() {
+                        // All items processed.
+                        Ok(ExecutionResult::next())
+                    } else {
+                        // Advance to next item.
+                        Ok(ExecutionResult::branch(
+                            vec![self.collection[next_index].clone()],
+                            Some(json!({"children_active": true, "current_index": next_index})),
+                        ))
+                    }
+                } else {
+                    Ok(ExecutionResult::persist(
+                        json!({"children_active": true, "current_index": current_index}),
+                    ))
+                }
+            } else {
+                // Start first item.
+                Ok(ExecutionResult::branch(
+                    vec![self.collection[current_index].clone()],
+                    Some(json!({"children_active": true, "current_index": current_index})),
+                ))
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{ExecutionPointer, PointerStatus};
+    use crate::primitives::test_helpers::*;
+
+    #[tokio::test]
+    async fn empty_collection_proceeds() {
+        let mut step = ForEachStep {
+            collection: vec![],
+            run_parallel: true,
+        };
+        let pointer = ExecutionPointer::new(0);
+        let wf_step = default_step();
+        let workflow = default_workflow();
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+
+        let result = step.run(&ctx).await.unwrap();
+        assert!(result.proceed);
+    }
+
+    #[tokio::test]
+    async fn parallel_branches_all_items() {
+        let mut step = ForEachStep {
+            collection: vec![json!(1), json!(2), json!(3)],
+            run_parallel: true,
+        };
+        let pointer = ExecutionPointer::new(0);
+        let wf_step = default_step();
+        let workflow = default_workflow();
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+
+        let result = step.run(&ctx).await.unwrap();
+        assert!(!result.proceed);
+        assert_eq!(result.branch_values, Some(vec![json!(1), json!(2), json!(3)]));
+    }
+
+    #[tokio::test]
+    async fn parallel_complete_proceeds() {
+        let mut step = ForEachStep {
+            collection: vec![json!(1), json!(2)],
+            run_parallel: true,
+        };
+        let mut pointer = ExecutionPointer::new(0);
+        pointer.persistence_data = Some(json!({"children_active": true}));
+
+        let wf_step = default_step();
+        let mut workflow = default_workflow();
+        let mut child = ExecutionPointer::new(1);
+        child.scope = vec![pointer.id.clone()];
+        child.status = PointerStatus::Complete;
+        workflow.execution_pointers.push(child);
+
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+        let result = step.run(&ctx).await.unwrap();
+        assert!(result.proceed);
+    }
+
+    #[tokio::test]
+    async fn sequential_starts_first_item() {
+        let mut step = ForEachStep {
+            collection: vec![json!("a"), json!("b"), json!("c")],
+            run_parallel: false,
+        };
+        let pointer = ExecutionPointer::new(0);
+        let wf_step = default_step();
+        let workflow = default_workflow();
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+
+        let result = step.run(&ctx).await.unwrap();
+        assert!(!result.proceed);
+        assert_eq!(result.branch_values, Some(vec![json!("a")]));
+        assert_eq!(
+            result.persistence_data,
+            Some(json!({"children_active": true, "current_index": 0}))
+        );
+    }
+
+    #[tokio::test]
+    async fn sequential_advances_to_next_item() {
+        let mut step = ForEachStep {
+            collection: vec![json!("a"), json!("b"), json!("c")],
+            run_parallel: false,
+        };
+        let mut pointer = ExecutionPointer::new(0);
+        pointer.persistence_data = Some(json!({"children_active": true, "current_index": 0}));
+
+        let wf_step = default_step();
+        let mut workflow = default_workflow();
+        let mut child = ExecutionPointer::new(1);
+        child.scope = vec![pointer.id.clone()];
+        child.status = PointerStatus::Complete;
+        workflow.execution_pointers.push(child);
+
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+        let result = step.run(&ctx).await.unwrap();
+        assert!(!result.proceed);
+        assert_eq!(result.branch_values, Some(vec![json!("b")]));
+        assert_eq!(
+            result.persistence_data,
+            Some(json!({"children_active": true, "current_index": 1}))
+        );
+    }
+
+    #[tokio::test]
+    async fn sequential_completes_after_last_item() {
+        let mut step = ForEachStep {
+            collection: vec![json!("a"), json!("b")],
+            run_parallel: false,
+        };
+        let mut pointer = ExecutionPointer::new(0);
+        pointer.persistence_data = Some(json!({"children_active": true, "current_index": 1}));
+
+        let wf_step = default_step();
+        let mut workflow = default_workflow();
+        let mut child = ExecutionPointer::new(1);
+        child.scope = vec![pointer.id.clone()];
+        child.status = PointerStatus::Complete;
+        workflow.execution_pointers.push(child);
+
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+        let result = step.run(&ctx).await.unwrap();
+        assert!(result.proceed);
+    }
+}