@tdd_issue @tdd_issue_10494
Feature: TDD Issue #10494 — _analyze_error node mutates state in-place instead of returning update dict
  As a developer using LangGraph
  I want AutoDebugAgent._analyze_error() to return a dict of state updates
  So that LangGraph can correctly merge state without double-applying mutations

  The current implementation mutates the input state dict in-place and returns
  the full state object, violating the LangGraph node contract. This test
  captures that violation so it can be tracked and fixed.

  LangGraph node functions must return a dict of updates (only the changed keys),
  not mutate the input state in-place and return the full state object. Returning
  the full mutated state can cause LangGraph to double-apply updates when merging
  state, leading to duplicate messages in the messages list.

  See CONTRIBUTING.md > Bug Fix Workflow > TDD Issue Test Tags.

  Scenario: Bug #10494 — _analyze_error returns the same state object instead of an update dict
    Given an AutoDebugAgent with a FakeListLLM for the mutation test
    And a state with an empty messages list for the mutation test
    When _analyze_error is called with the state for the mutation test
    Then the analyze_error result should not be the same object as the input state
    And the original messages list should not have been mutated by analyze_error
    And the analyze_error result should be a plain dict of updates
