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/saga_container.rs

@@ -0,0 +1,151 @@
+use async_trait::async_trait;
+use serde_json::json;
+
+use crate::models::ExecutionResult;
+use crate::traits::step::{StepBody, StepExecutionContext};
+
+/// A container step for saga transactions.
+/// Manages child step execution and compensation on failure.
+pub struct SagaContainerStep {
+    pub revert_children_after_compensation: bool,
+}
+
+impl Default for SagaContainerStep {
+    fn default() -> Self {
+        Self {
+            revert_children_after_compensation: true,
+        }
+    }
+}
+
+#[async_trait]
+impl StepBody for SagaContainerStep {
+    async fn run(&mut self, context: &StepExecutionContext<'_>) -> crate::Result<ExecutionResult> {
+        let children_active = context
+            .persistence_data
+            .and_then(|d| d.get("children_active"))
+            .and_then(|v| v.as_bool())
+            .unwrap_or(false);
+
+        let compensating = context
+            .persistence_data
+            .and_then(|d| d.get("compensating"))
+            .and_then(|v| v.as_bool())
+            .unwrap_or(false);
+
+        if compensating {
+            // We are in compensation mode, check if compensation children are done.
+            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, "compensating": true}),
+                ))
+            }
+        } else if children_active {
+            let mut scope = context.execution_pointer.scope.clone();
+            scope.push(context.execution_pointer.id.clone());
+
+            // Check if compensation is needed by looking for do_compensate on the step.
+            if context.step.do_compensate {
+                // Trigger compensation.
+                Ok(ExecutionResult::branch(
+                    vec![json!(null)],
+                    Some(json!({"children_active": true, "compensating": true})),
+                ))
+            } else if context.workflow.is_branch_complete(&scope) {
+                // Normal completion.
+                Ok(ExecutionResult::next())
+            } else {
+                Ok(ExecutionResult::persist(json!({"children_active": true})))
+            }
+        } else {
+            // First run: branch for children.
+            Ok(ExecutionResult::branch(
+                vec![json!(null)],
+                Some(json!({"children_active": true})),
+            ))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{ExecutionPointer, PointerStatus, WorkflowStep};
+    use crate::primitives::test_helpers::*;
+
+    #[tokio::test]
+    async fn first_run_branches_for_children() {
+        let mut step = SagaContainerStep::default();
+        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!(null)]));
+        assert_eq!(result.persistence_data, Some(json!({"children_active": true})));
+    }
+
+    #[tokio::test]
+    async fn normal_completion_when_children_done() {
+        let mut step = SagaContainerStep::default();
+        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 compensation_triggered_when_do_compensate() {
+        let mut step = SagaContainerStep::default();
+        let mut pointer = ExecutionPointer::new(0);
+        pointer.persistence_data = Some(json!({"children_active": true}));
+
+        let mut wf_step = WorkflowStep::new(0, "SagaContainer");
+        wf_step.do_compensate = true;
+
+        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!(null)]));
+        assert_eq!(
+            result.persistence_data,
+            Some(json!({"children_active": true, "compensating": true}))
+        );
+    }
+
+    #[tokio::test]
+    async fn compensation_complete_proceeds() {
+        let mut step = SagaContainerStep::default();
+        let mut pointer = ExecutionPointer::new(0);
+        pointer.persistence_data = Some(json!({"children_active": true, "compensating": 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::Compensated;
+        workflow.execution_pointers.push(child);
+
+        let ctx = make_context(&pointer, &wf_step, &workflow);
+        let result = step.run(&ctx).await.unwrap();
+        assert!(result.proceed);
+    }
+}