1.4.0 cannot parse the final stream activity emitted by the .NET SDK (`StreamInfo.stream_sequence` is required)

[bwilde-castle]

1.4.0 routes streaminfo entities through the typed StreamInfo, whose stream_sequence: int has no default. Agents-for-net deliberately omits that field on a stream's final message, so from 1.4.0 the Python parser rejects final activities produced by the .NET SDK. The final activity is the one carrying the answer, so the whole turn is lost.

Repro

The entity shape Agents-for-net emits — StreamType / StreamId / StreamResult, no StreamSequence:

uv run --no-project --with "microsoft-agents-activity==1.4.0" --with pyjwt python -c "
from microsoft_agents.activity import Activity
print(Activity.model_validate({'type': 'message', 'text': 'this is a test', 'entities': [
    {'type': 'streaminfo', 'streamType': 'final', 'streamId': 'a-0000l', 'streamResult': 'success'}]}))
"

ValidationError: 1 validation error for Activity
entities.streamSequence
  Field required [type=missing, input_value={'type': 'streaminfo', 's...tream_result': 'success'}, input_type=dict]

Parses on 0.9.1 through 1.3.0, raises on 1.4.0. Intermediate streaming chunks, which do carry streamSequence, are unaffected.

The three SDKs disagree, and only .NET's output is unrepresentable in Python

sender	streamSequence on the final message
Agents-for-net StreamingResponse.cs:583	omitted — the assignment is commented out, while the streaming branch 15 lines below sets it
Agents-for-js streamingResponse.ts:453	set
Agents-for-python streaming_response.py:322	set

.NET's model permits the absence — StreamInfo.cs declares public int? StreamSequence { get; set; }, nullable with no [JsonRequired]. Python declares stream_sequence: int. (The published protocol agrees with .NET: "For the final message, streamSequence must not be set.")

That split is plausibly why this wasn't caught — the Python and JS senders both emit the field, so their own round-trip tests pass. Only cross-stack traffic hits it: a Python client reading a .NET-produced stream. That is how we ran into it, via microsoft-agents-copilotstudio-client.

Suggested fix

stream_sequence: int | None = None