fix(plan): wrap plan tree JSON/YAML output in spec-required command envelope

Closes #11044

CHANGELOG.md

@@ -132,6 +132,15 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 
+- **plan tree JSON/YAML output wrapped in spec-required envelope (#11044): The
+  decision tree CLI command now wraps machine-readable output (JSON and YAML formats)
+  in the spec-required command envelope structure (`command`, `status`, `exit_code`,
+  `data`, `timing`, `messages`). Previously the command field was empty for JSON/YAML
+  output. The "no decisions found" case also returns structured JSON/YAML output
+  instead of plain text. Updated BDD step definitions in
+  ``features/steps/plan_explain_steps.py`` to expect an envelope dict and verify all
+  spec-required envelope keys are present.
+
 - **Error suppression removed from `reactive_registry_adapter.py`** (#9060): Removed two `try...except Exception:` blocks in `register_registry_agents()` that silently suppressed errors, violating the CONTRIBUTING.md fail-fast policy. Exceptions from `actor_registry.list_actors()` and the route bridge refresh now propagate to the caller instead of being swallowed. Added Behave scenarios verifying RuntimeError, AttributeError, and TypeError propagation.
 
 - **Implementation Supervisor PR Compliance Checklist** (#9824): Added a mandatory

CONTRIBUTORS.md

@@ -11,6 +11,8 @@
 # Details
 
 Below are some of the specific details of various contributions.
+* HAL 9000 has contributed the plan tree command JSON/YAML envelope fix (#11044): wrapped machine-readable output in spec-required command envelope with proper command identification, status field, and error handling for empty decision lists.
+
 
 * Jeffrey Phillips Freeman has acted as Lead Developer, daily contributor, and Project Owner.
 * Brent E. Edwards has contributed quality assurance, test coverage, and CI pipeline improvements.

features/steps/plan_explain_steps.py

@@ -287,8 +287,21 @@ def step_build_tree_empty(context: Context) -> None:
 
 @when("I format the tree as json")
 def step_format_tree_json(context: Context) -> None:
+    from contextlib import redirect_stdout
+    from io import StringIO
+
     tree = build_decision_tree(context.pe_decisions)
-    context.pe_tree_json = _capture_format_output(tree, "json")
+    buf = StringIO()
+    with redirect_stdout(buf):
+        result = format_output(
+            tree,
+            'json',
+            command='plan tree',
+            status='ok',
+            exit_code=0,
+            messages=[{'level': 'info', 'text': 'Decision tree'}],
+        )
+    context.pe_tree_json = (result or buf.getvalue()).rstrip('\n')
 
 
 @when("I format the tree as yaml")