fix: raise ValueError on append to nonexistent artifact#1040

naveenkumarbaskaran wants to merge 1 commit intoa2aproject:maina2aproject/a2a-python:mainfrom

naveenkumarbaskaran:fix/raise-on-append-unknown-artifactnaveenkumarbaskaran/a2a-python:fix/raise-on-append-unknown-artifactCopy head branch name to clipboard