stream_lifecycle

Validator for LangChain content-block protocol event streams.

Checks that an event stream emitted by a chat model (via stream_v2, or by the compat bridge's chunks_to_events / message_to_events) conforms to the protocol lifecycle rules:

• message-start opens and message-finish closes the stream.
• Content blocks do not interleave: each block runs content-block-start → optional content-block-deltas → content-block-finish before the next block begins.
• Wire indices on content-block events are sequential uint values starting at 0.
• For deltaable block types (text, reasoning, tool_call_chunk, server_tool_call_chunk), accumulated delta content matches the final payload delivered on content-block-finish.

The validator accepts any iterable of protocol event dicts. It raises AssertionError on the first violation with a descriptive message.