A2A ships an official CLI after its community and SDK clients drifted apart

Under `--exec`, the contract has three rules. The CLI writes the incoming message to the program's stdin and returns whatever it prints on stdout as the response ^[9]. Exit 0 succeeds and any non-zero code fails ^[9]. Stderr is logged and attached to the failure ^[9]. By that contract, `cat` is an A2A agent ^[13].

We think tying task outcome to process exit status is the right design. Exit status is the signal a CI runner already checks. Attaching stderr to the failure keeps the error text with the task that failed ^[9].

Streaming depends on the wrapped program too. Without `--chunk`, the server waits for the script to exit and returns everything it printed as one response ^[10]. With `--chunk` set to a newline, each line goes out as its own streamed piece ^[10]. That puts the program's output buffering inside the streaming path. The project's sample script calls `sys.stdout.flush()` after every line, and its docstring says to run it with `python3 -u` "so stdout is unbuffered and chunks stream promptly" ^[11].

For pipelines, the post promises protocol-native JSON output and predictable exit codes ^[1]. Output shape was one of the things the older community and SDK clients disagreed on, along with command names, flags and transport handling ^[4]. Building the official client from the Go SDK's CLI ^[5] makes that SDK's choices the reference point. In our view the official label ends the drift only when the clients in other languages converge on it or retire. The post does not say whether any of them will be deprecated.