extractResponseText in delegation.go had no unit tests. It extracts text
from A2A JSON-RPC response bodies by walking result.parts and
result.artifacts[*].parts arrays. Tests cover: non-JSON fallback, valid
JSON with no result, result is not a map, parts with text kind, parts
with non-text kind (image skipped → raw body), multiple parts (returns
first text), artifacts with nested text parts, artifacts with non-text
kind, empty parts/artifacts arrays, and empty text string.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
