feat(wfe-core): add typed workflow schema system

SchemaType enum with inline syntax parsing: "string", "string?",
"list<number>", "map<string>", nested generics. WorkflowSchema
validates inputs/outputs against type declarations at both compile
time and runtime. 39 tests for parse and validate paths.

wfe-core/src/traits/middleware.rs

@@ -68,6 +68,7 @@ mod tests {
             step: &step,
             workflow: &instance,
             cancellation_token: tokio_util::sync::CancellationToken::new(),
+            host_context: None,
         };
         mw.pre_step(&ctx).await.unwrap();
     }
@@ -86,6 +87,7 @@ mod tests {
             step: &step,
             workflow: &instance,
             cancellation_token: tokio_util::sync::CancellationToken::new(),
+            host_context: None,
         };
         let result = ExecutionResult::next();
         mw.post_step(&ctx, &result).await.unwrap();

wfe-core/src/traits/mod.rs

@@ -17,4 +17,4 @@ pub use persistence::{
 pub use queue::QueueProvider;
 pub use registry::WorkflowRegistry;
 pub use search::{Page, SearchFilter, SearchIndex, WorkflowSearchResult};
-pub use step::{StepBody, StepExecutionContext, WorkflowData};
+pub use step::{HostContext, StepBody, StepExecutionContext, WorkflowData};

wfe-core/src/traits/step.rs

@@ -11,8 +11,18 @@ pub trait WorkflowData: Serialize + DeserializeOwned + Send + Sync + Clone + 'st
 /// Blanket implementation: any type satisfying the bounds is WorkflowData.
 impl<T> WorkflowData for T where T: Serialize + DeserializeOwned + Send + Sync + Clone + 'static {}
 
+/// Context for steps that need to interact with the workflow host.
+/// Implemented by WorkflowHost to allow steps like SubWorkflow to start child workflows.
+pub trait HostContext: Send + Sync {
+    fn start_workflow(
+        &self,
+        definition_id: &str,
+        version: u32,
+        data: serde_json::Value,
+    ) -> std::pin::Pin<Box<dyn std::future::Future<Output = crate::Result<String>> + Send + '_>>;
+}
+
 /// Context available to a step during execution.
-#[derive(Debug)]
 pub struct StepExecutionContext<'a> {
     /// The current item when iterating (ForEach).
     pub item: Option<&'a serde_json::Value>,
@@ -26,6 +36,22 @@ pub struct StepExecutionContext<'a> {
     pub workflow: &'a WorkflowInstance,
     /// Cancellation token.
     pub cancellation_token: tokio_util::sync::CancellationToken,
+    /// Host context for starting child workflows. None if not available.
+    pub host_context: Option<&'a dyn HostContext>,
+}
+
+// Manual Debug impl since dyn HostContext is not Debug.
+impl<'a> std::fmt::Debug for StepExecutionContext<'a> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("StepExecutionContext")
+            .field("item", &self.item)
+            .field("execution_pointer", &self.execution_pointer)
+            .field("persistence_data", &self.persistence_data)
+            .field("step", &self.step)
+            .field("workflow", &self.workflow)
+            .field("host_context", &self.host_context.is_some())
+            .finish()
+    }
 }
 
 /// The core unit of work in a workflow. Each step implements this trait.