Feature: LangGraph state additional coverage
  As a developer
  I want to exercise uncovered state management branches
  So that langgraph/state.py gains higher coverage

  Background:
    Given the state management system is available

  Scenario: Merge mode trims messages beyond retention limit
    Given I have a GraphState starting with 49 messages
    And I have merge updates containing 5 new messages
    When I merge the updates into the state
    Then the message list should be trimmed to 50 messages
    And the newest message should be retained after trimming

  Scenario: Append mode trims messages beyond retention limit 
    Given the state management system is available
    Given I have a GraphState starting with 50 messages
    And I have append updates containing 5 new messages
    When I append the updates into the state
    Then the message list should be trimmed to 50 messages after append
    And the newest appended message should be retained after trimming


  Scenario: Time travel history is recorded and trimmed
    Given I have a StateManager with time travel enabled and history size 2
    When I perform 4 sequential state updates with time travel
    Then only the two most recent history snapshots should remain
    And the earliest snapshots should be discarded

  Scenario: Automatic checkpoint is saved at interval
    Given I have a StateManager with checkpointing enabled and interval 1
    When I perform 2 sequential state updates with checkpointing
    Then a checkpoint file should exist in the directory
    And checkpoint saving should have been triggered

  Scenario: Time travel clamps when steps exceed history
    Given I have a StateManager with time travel history of 2 snapshots
    When I request time travel 5 steps back
    Then time travel should return the earliest available snapshot
    And the returned state should reflect the earliest snapshot