diff --git a/features/steps/plan_explain_steps.py b/features/steps/plan_explain_steps.py
index 52f66681a..a7d8c6c19 100644
--- a/features/steps/plan_explain_steps.py
+++ b/features/steps/plan_explain_steps.py
@@ -402,7 +402,12 @@ def step_roots_no_children(context: Context) -> None:
 @then("the json tree output should be valid json")
 def step_tree_json_valid(context: Context) -> None:
     parsed = json.loads(context.pe_tree_json)
-    assert isinstance(parsed, list), "Expected a JSON array"
+    assert isinstance(parsed, dict), (
+        f"Expected JSON envelope (dict), got {type(parsed).__name__}"
+    )
+    _ENVELOPE_KEYS = {"command", "status", "exit_code", "data", "timing", "messages"}
+    missing = _ENVELOPE_KEYS - set(parsed.keys())
+    assert not missing, f"Envelope missing required fields: {missing}"
 
 
 @then('the json tree output should contain "{text}"')
diff --git a/src/cleveragents/cli/commands/plan.py b/src/cleveragents/cli/commands/plan.py
index a91c9950b..430a41abb 100644
--- a/src/cleveragents/cli/commands/plan.py
+++ b/src/cleveragents/cli/commands/plan.py
@@ -4154,9 +4154,7 @@ def tree_decisions_cmd(
 
     if fmt in (OutputFormat.JSON, OutputFormat.YAML):
         console.print(
-            format_output(
-                tree_data, fmt, command="plan tree", status="ok", exit_code=0
-            )
+            format_output(tree_data, fmt, command="plan tree", status="ok", exit_code=0)
         )
     elif fmt == OutputFormat.TABLE:
         # Flatten for table view