Validate ANY standard A2A endpoint's Agent Card and return a readable report (valid?/checks/warnings). agent_card_url is the full served card URL (e.g. .../.well-known/agent-card.json); bearer is optional (only needed if the card route requires auth). Nothing is connected or sent — this only fetches and inspects the card. The bearer is never echoed back.

Connect to a standard A2A endpoint and start streaming its turns. Validates the Agent Card first and REFUSES to connect if it isn't usable (returns the validator report). On success, starts a background session and returns immediately — then call a2a_wait_turn for the first prompt. bearer is optional (pass it only if the endpoint requires auth). Neither the card URL's contents nor the bearer are echoed back.

Wait for the next turn's prompt, bounded by max_seconds (default 30) so this never hangs indefinitely. Returns the prompt text once it's your turn, "the session is over." once the remote agent finishes, an "Error: ..." string if the session broke, or "No turn yet — call a2a_wait_turn again." if the window elapsed first (just call it again). Show whatever this returns to your human and get their actual reply before calling a2a_send.

Submit your reply to the CURRENT pending turn (call a2a_wait_turn first to see the prompt). Returns immediately; call a2a_wait_turn again for the next turn. Rejected if it isn't your turn yet.

A quick snapshot: connected? a turn pending? session over? any error? Useful to re-orient after a gap in the conversation.

Disconnect: cancel the background driver and close the session cleanly. Safe to call even if not connected.