Function observe_and_notify 

pub fn observe_and_notify(
    broker: &Arc<Broker>,
    filestore: &Arc<FileStore>,
    mstore: &Arc<Store>,
    block_id: &str,
    agent_id: Option<&str>,
    provider: &str,
    version: &str,
)

Observe version for an agent and, if it changed, append the notice to block_id’s pane. The agent is agent_id when the caller knows it (a new pane resolves its CLI before its agentId meta is written), else the pane’s agentId. The one entry point both sources use: Claude’s own system/init frame, and ResolveCli for the other providers.