Feature: Sandbox protocol coverage boost
  Exercise uncovered lines in infrastructure/sandbox/protocol.py including
  SandboxStatus.assert_transition error path and Sandbox Protocol default stubs.

  # ---------------------------------------------------------------
  # SandboxStatus.assert_transition – invalid transition raises error
  # Covers lines 121-123
  # ---------------------------------------------------------------

  Scenario: assert_transition raises SandboxStateError for invalid transition
    Given spcb sandbox status "cleaned_up" and target status "active"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "cleaned_up -> active"

  Scenario: assert_transition raises SandboxStateError for pending to committed
    Given spcb sandbox status "pending" and target status "committed"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "pending -> committed"

  Scenario: assert_transition raises SandboxStateError for committed to active
    Given spcb sandbox status "committed" and target status "active"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "committed -> active"

  Scenario: assert_transition succeeds for valid pending to created transition
    Given spcb sandbox status "pending" and target status "created"
    When spcb assert_transition is called with those statuses
    Then spcb no exception should be raised

  # ---------------------------------------------------------------
  # Sandbox Protocol default property/method stubs
  # Covers lines 223, 228, 233, 248, 263, 278, 290, 301
  # ---------------------------------------------------------------

  Scenario: Protocol sandbox_id default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the sandbox_id property is accessed
    Then spcb the result should be None

  Scenario: Protocol status default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the status property is accessed
    Then spcb the result should be None

  Scenario: Protocol context default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the context property is accessed
    Then spcb the result should be None

  Scenario: Protocol create default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the create method is called with plan_id "test-plan"
    Then spcb the result should be None

  Scenario: Protocol get_path default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the get_path method is called with path "src/main.py"
    Then spcb the result should be None

  Scenario: Protocol commit default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the commit method is called with message "test commit"
    Then spcb the result should be None

  Scenario: Protocol rollback default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the rollback method is called
    Then spcb the result should be None

  Scenario: Protocol cleanup default stub returns None
    Given spcb a bare Sandbox protocol subclass instance
    When spcb the cleanup method is called
    Then spcb the result should be None

  # ---------------------------------------------------------------
  # Additional assert_transition edge cases for branch coverage
  # ---------------------------------------------------------------

  Scenario: assert_transition raises for every terminal-state outbound attempt
    Given spcb sandbox status "cleaned_up" and target status "pending"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "cleaned_up -> pending"

  Scenario: assert_transition raises for errored to active
    Given spcb sandbox status "errored" and target status "active"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "errored -> active"

  Scenario: assert_transition raises for rolled_back to committed
    Given spcb sandbox status "rolled_back" and target status "committed"
    When spcb assert_transition is called with those statuses
    Then spcb a SandboxStateError should be raised
    And spcb the error message should contain "rolled_back -> committed"