Add table-driven test with case and whitespace variants (ALPHA,
" Alpha ", " alpha ") that should all be caught by the self-check
after normalization.
Ref: #2148
12 test cases covering:
- success path with result attribution
- agent_id validation (missing, empty, whitespace, wrong type)
- task validation (missing, empty, whitespace)
- permission denied / allowed via allowlist checker
- self-delegation blocked
- nil spawner, spawner error, nil result from spawner
- open access when no allowlist checker is set
Ref: #2148