PR #477 added _A2A_BOUNDARY_START/END wrapping to tool_delegate_task's
success path. Three tests in test_delegation_sync_via_polling.py were
still asserting exact raw strings and broke:
test_flag_off_uses_send_a2a_message_not_polling
test_queued_sentinel_triggers_polling_fallback
test_non_queued_send_result_does_not_trigger_fallback
Fix: check for boundary markers + inner content instead of exact match.
Import _A2A_BOUNDARY_START/END from _sanitize_a2a in the affected
test methods.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>