Enforce API contracts via MagicMock spec in test_eknowledge.py tests

[chigwell]

User Story
As a software engineer,
I want MagicMock instances in test_eknowledge.py to enforce API contracts via spec=True
so that unintended method calls or attribute accesses during testing raise immediate errors.

Background
Current MagicMock calls in TestExecuteGraphGeneration (e.g., self.mock_llm = MagicMock()) lack specification binding. This allows:

• Calls to non-existent methods on the mocked ChatLLM7 class
• Silent failures when API contracts change
• False test passes due to overly permissive mocks

Specific risk areas include tests like test_single_chunk_success and test_llm_returns_malformed_node, where loose mocks in tests/test_eknowledge.py could mask interface mismatches with the real ChatLLM7 implementation.

Acceptance Criteria

• Update all MagicMock instantiations in TestExecuteGraphGeneration class:

  # Before
  self.mock_llm = MagicMock()
  
  # After 
  self.mock_llm = MagicMock(spec=ChatLLM7)

• Apply spec=True to MagicMock calls in test methods like test_llm_returns_no_nodes and test_llm_invocation_error_then_success
• Verify tests fail when:
  1. Adding an invalid method call (e.g., self.mock_llm.nonexistent_method())
  2. Accessing undefined attributes on mock objects
• Ensure all existing tests pass after updates, confirming spec compliance
• Confirm error messages explicitly reference mismatched API contracts (e.g., "Mock object has no attribute 'nonexistent_method'")