refactor: rename status to $status, default to _ when absent

- evaluate() reads $status instead of status, defaults to _ when missing
- Update all YAML examples and .workflows to use $status
- Update cli-workflow resolveEvaluateArgs to use $status
- 10 moderator tests pass including new default _ test
- Single-exit roles no longer need to declare status field

Phase 1 of #499 (closes #500)

examples/solve-issue.yaml

@@ -27,13 +27,13 @@ roles:
     frontmatter:
       type: object
       properties:
-        status:
+        $status:
           enum: ["_"]
         repoPath:
           type: string
         plan:
           type: string
-      required: [status, repoPath, plan]
+      required: [$status, repoPath, plan]
   developer:
     description: "Implements code changes"
     goal: "You are a developer agent. You implement code changes according to plans."
@@ -52,7 +52,7 @@ roles:
     frontmatter:
       type: object
       properties:
-        status:
+        $status:
           enum: ["_"]
         filesChanged:
           type: array
@@ -60,7 +60,7 @@ roles:
             type: string
         summary:
           type: string
-      required: [status, filesChanged, summary]
+      required: [$status, filesChanged, summary]
   reviewer:
     description: "Reviews code changes"
     goal: "You are a code reviewer. You review implementations for correctness and quality."
@@ -75,11 +75,11 @@ roles:
     frontmatter:
       type: object
       properties:
-        status:
+        $status:
           enum: ["approved", "rejected"]
         comments:
           type: string
-      required: [status, comments]
+      required: [$status, comments]
 graph:
   $START:
     _: { role: "planner", prompt: "Analyze the issue described in the task and produce a detailed implementation plan." }