Brings in master a8d675ecc92, which reverts the agent controller of #6418,
together with the composer's image upload on add.
The agent-controller message delivery Agent Note follows master's deletion.
The ui-conversation README keeps the read-only sending paragraph and takes
the image upload sentences. Service orchestration keeps both new sendSession
cases, and the refused-send reference case takes master's newSession
submission fact. README pairings are recorded again.