feat(commands): add handoffs support for speckit compatibility (#410)

* feat(commands): add handoffs support for speckit compatibility

- Upgrade frontmatter parser to use js-yaml for complex YAML support
- Add HandoffDefinition interface for speckit-style workflow transitions
- Update CommandFrontmatter and CommandDefinition to include handoffs
- Add comprehensive tests for backward compatibility and complex YAML
- Fix type parameters in auto-slash-command and slashcommand tools

Closes #407

* fix(frontmatter): use JSON_SCHEMA for security and add extra fields tolerance tests

- Use JSON_SCHEMA in yaml.load() to prevent code execution via YAML tags
- Add tests to verify extra fields in frontmatter don't cause failures
- Address Greptile security review comment

---------

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/features/claude-code-command-loader/loader.ts

@@ -78,6 +78,7 @@ $ARGUMENTS
         model: sanitizeModelField(data.model, isOpencodeSource ? "opencode" : "claude-code"),
         subtask: data.subtask,
         argumentHint: data["argument-hint"],
+        handoffs: data.handoffs,
       }
 
       commands.push({

src/features/claude-code-command-loader/types.ts

@@ -1,5 +1,21 @@
 export type CommandScope = "user" | "project" | "opencode" | "opencode-project"
 
+/**
+ * Handoff definition for command workflows.
+ * Based on speckit's handoff pattern for multi-agent orchestration.
+ * @see https://github.com/github/spec-kit
+ */
+export interface HandoffDefinition {
+  /** Human-readable label for the handoff action */
+  label: string
+  /** Target agent/command identifier (e.g., "speckit.tasks") */
+  agent: string
+  /** Pre-filled prompt text for the handoff */
+  prompt: string
+  /** If true, automatically executes after command completion; if false, shows as suggestion */
+  send?: boolean
+}
+
 export interface CommandDefinition {
   name: string
   description?: string
@@ -8,6 +24,8 @@ export interface CommandDefinition {
   model?: string
   subtask?: boolean
   argumentHint?: string
+  /** Handoff definitions for workflow transitions */
+  handoffs?: HandoffDefinition[]
 }
 
 export interface CommandFrontmatter {
@@ -16,6 +34,8 @@ export interface CommandFrontmatter {
   agent?: string
   model?: string
   subtask?: boolean
+  /** Handoff definitions for workflow transitions */
+  handoffs?: HandoffDefinition[]
 }
 
 export interface LoadedCommand {