Fixes a bug where the root decision was recorded as 'strategy_choice' instead of
the correct 'prompt_definition' type during the Strategize phase. The decision tree
now correctly records the plan's prompt/description as the root decision, ensuring
proper decision tree structure and downstream decision evaluation.

Changes:
- Modified start_strategize() to record prompt_definition as the root decision
- Updated decision question to 'What is the plan prompt?'
- Set chosen_option to plan.description with fallback to action_name or plan_id
- Added test scenario to verify root decision type is prompt_definition

Closes #9061

@@ -0,0 +68,4 @@
+
+@given("the auto debug state mutation module is imported")
+def step_module_imported(context: Any) -> None:
+    """Verify the auto_debug module is importable."""

@@ -0,0 +7,4 @@
+    Given the auto debug state mutation module is imported
+
+  Scenario: _analyze_error does not mutate the original state object
+    Given an auto debug agent for mutation testing

@@ -0,0 +62,4 @@
+        "current_fix": {},
+        "fix_validated": False,
+    }
+    state.update(overrides)  # type: ignore[typeddict-item]

@@ -0,0 +6,4 @@
+  Background:
+    Given the auto debug state mutation module is imported
+
+  Scenario: _analyze_error does not mutate the original state object