Feature: LangGraph state branch coverage
  As a developer
  I want to exercise remaining uncovered branches
  So that langgraph/state.py reaches higher coverage

  Background:
    Given the state management system is available

  Scenario: Replace mode overwrites existing fields
    Given I have a GraphState with metadata {"original": 1} and current node "old"
    When I replace the state with updates containing metadata {"new": 2} and current node "new"
    Then the state's metadata should equal {"new": 2}
    And the state's current node should equal "new"

  Scenario: Merge mode merges metadata dictionaries
    Given I have a GraphState with metadata {"alpha": 1}
    And I have merge metadata updates {"beta": 2}
    When I merge metadata updates into the state
    Then the state's metadata should contain keys "alpha" and "beta"

  Scenario: Append mode appends a single message item
    Given I have a GraphState with 1 message
    When I append a single message with id 99 into the state
    Then the state's messages should end with id 99
    And the message list length should be 2

  Scenario: Save checkpoint without directory is a no-op
    Given I have a StateManager without checkpointing
    When I invoke checkpoint saving manually
    Then the update count should remain at 0

  Scenario: Load checkpoint restores state and counters
    Given I have a checkpoint file with execution count 7 and metadata {"restored": true}
    When I load the checkpoint into a StateManager
    Then the manager state should include metadata {"restored": true}
    And the manager update count should be 7

  Scenario: Latest checkpoint returns None when missing
    Given I have a StateManager without checkpointing
    When I request the latest checkpoint
    Then no checkpoint path should be returned

  Scenario: Latest checkpoint selects the most recent file
    Given I have a StateManager with two checkpoints written at different times
    When I request the latest checkpoint
    Then the newest checkpoint path should be returned

  Scenario: Time travel without history returns None
    Given I have a StateManager with time travel disabled
    When I request time travel
    Then the returned time travel state should be None

  Scenario: Clear history and reset restore initial state
    Given I have a StateManager with time travel history entries
    When I clear the history and then reset with metadata {"reset": true}
    Then the history should be empty after reset
    And the execution count should be zero after reset
    And the state metadata should include {"reset": true}