Duplex echo example

Use the managed streaming handler as the smallest duplex example. It is a handler, not a standalone child. Its descriptor needs io_mode="bidirectional" and both input and output chunk schemas; the initial request schema is separate from each chunk schema.

Wire it into the control loop

On StreamInvoke, start an owned task with streams.execute_stream(startup, message, handler). Keep answering Health on the primary connection. On shutdown or lost control connection, cancel and await the task before closing resources. Do not put the entire stream inline inside the health loop.

Exercise the caller sequence

1. Discover the descriptor and negotiate its exact id, version and revision.
2. Open through the Fabric caller API and check open_result.ok before sending input.
3. Consume provider frames while sending bounded input chunks.
4. Call session.input.complete() to half-close input.
5. Keep reading output until its terminal; inspect failure or cancellation, not just the chunks received.

skulk.extensions caller examples show this side of the contract. A managed child does not directly create that caller context. The host callback channel is a fixed management contract; it is not a general-purpose Fabric streaming client.

Cases to test

Send zero chunks, one chunk and many chunks. Try a slow output consumer, cancel while input is open, lose the media connection and send an invalid chunk. Confirm ordered output begins at sequence one after Skulk™’s started frame, exactly one terminal is emitted and cleanup finishes before successful terminal delivery.

Raw media remains binary. Do not base64 it into JSON or publish it as application telemetry. See streams reference for exact helper signatures and bounds.