feat(wfe-yaml): add multi-workflow YAML and typed input/output schemas

YamlWorkflowFile supports both single (workflow:) and multi (workflows:)
formats. WorkflowSpec gains typed inputs/outputs declarations.
Type string parser for inline types ("string?", "list<number>", etc.).
load_workflow_from_str returns Vec<CompiledWorkflow>.
Backward-compatible load_single_workflow_from_str convenience function.

wfe-yaml/src/lib.rs

@@ -3,6 +3,7 @@ pub mod error;
 pub mod executors;
 pub mod interpolation;
 pub mod schema;
+pub mod types;
 pub mod validation;
 
 use std::collections::HashMap;
@@ -10,29 +11,78 @@ use std::collections::HashMap;
 use crate::compiler::CompiledWorkflow;
 use crate::error::YamlWorkflowError;
 
-/// Load a workflow from a YAML file path, applying variable interpolation.
+/// Load workflows from a YAML file path, applying variable interpolation.
+/// Returns a Vec of compiled workflows (supports multi-workflow files).
 pub fn load_workflow(
     path: &std::path::Path,
     config: &HashMap<String, serde_json::Value>,
 ) -> Result<CompiledWorkflow, YamlWorkflowError> {
     let yaml = std::fs::read_to_string(path)?;
-    load_workflow_from_str(&yaml, config)
+    load_single_workflow_from_str(&yaml, config)
 }
 
-/// Load a workflow from a YAML string, applying variable interpolation.
+/// Load workflows from a YAML string, applying variable interpolation.
+/// Returns a Vec of compiled workflows (supports multi-workflow files).
 pub fn load_workflow_from_str(
     yaml: &str,
     config: &HashMap<String, serde_json::Value>,
-) -> Result<CompiledWorkflow, YamlWorkflowError> {
+) -> Result<Vec<CompiledWorkflow>, YamlWorkflowError> {
     // Interpolate variables.
     let interpolated = interpolation::interpolate(yaml, config)?;
 
-    // Parse YAML.
-    let workflow: schema::YamlWorkflow = serde_yaml::from_str(&interpolated)?;
+    // Parse YAML as multi-workflow file.
+    let file: schema::YamlWorkflowFile = serde_yaml::from_str(&interpolated)?;
 
-    // Validate.
-    validation::validate(&workflow.workflow)?;
+    let specs = resolve_workflow_specs(file)?;
 
-    // Compile.
-    compiler::compile(&workflow.workflow)
+    // Validate (multi-workflow validation includes per-workflow + cross-references).
+    validation::validate_multi(&specs)?;
+
+    // Compile each workflow.
+    let mut results = Vec::with_capacity(specs.len());
+    for spec in &specs {
+        results.push(compiler::compile(spec)?);
+    }
+
+    Ok(results)
+}
+
+/// Load a single workflow from a YAML string. Returns an error if the file
+/// contains more than one workflow. This is a backward-compatible convenience
+/// function.
+pub fn load_single_workflow_from_str(
+    yaml: &str,
+    config: &HashMap<String, serde_json::Value>,
+) -> Result<CompiledWorkflow, YamlWorkflowError> {
+    let mut workflows = load_workflow_from_str(yaml, config)?;
+    if workflows.len() != 1 {
+        return Err(YamlWorkflowError::Validation(format!(
+            "Expected single workflow, got {}",
+            workflows.len()
+        )));
+    }
+    Ok(workflows.remove(0))
+}
+
+/// Resolve a YamlWorkflowFile into a list of WorkflowSpecs.
+fn resolve_workflow_specs(
+    file: schema::YamlWorkflowFile,
+) -> Result<Vec<schema::WorkflowSpec>, YamlWorkflowError> {
+    match (file.workflow, file.workflows) {
+        (Some(single), None) => Ok(vec![single]),
+        (None, Some(multi)) => {
+            if multi.is_empty() {
+                return Err(YamlWorkflowError::Validation(
+                    "workflows list is empty".to_string(),
+                ));
+            }
+            Ok(multi)
+        }
+        (Some(_), Some(_)) => Err(YamlWorkflowError::Validation(
+            "Cannot specify both 'workflow' and 'workflows' in the same file".to_string(),
+        )),
+        (None, None) => Err(YamlWorkflowError::Validation(
+            "Must specify either 'workflow' or 'workflows'".to_string(),
+        )),
+    }
 }