Add add_attachment and reset to StreamingResponse

[Copilot]

StreamingResponse only supported bulk-replacing attachments via set_attachments(). This adds an incremental add_attachment() method and a reset() method, matching the C# SDK (Agents-for-net#878).

Changes

StreamingResponse (streaming_response.py)

• add_attachment(attachment) — appends a single Attachment to the final message; raises ValueError on None; lazy-initializes the list; composable with set_attachments()
• reset() — waits for the queue to drain, then restores all state to initial values (including clearing _attachments)
• _initialize_state() — private helper extracted to hold all default field assignments; called by both __init__ and reset() to keep them in sync

Tests (test_streaming_response.py)

Four new tests: attachment included in final activity, ValueError on None, attachments cleared after reset(), multiple calls accumulate correctly.

Usage

card = Attachment(
    content_type="application/vnd.microsoft.card.adaptive",
    content=my_adaptive_card_payload,
)
context.streaming_response.add_attachment(card)
context.streaming_response.queue_text_chunk("Here is the information you requested:")
await context.streaming_response.end_stream()

[Copilot]

Pull request overview

Adds incremental attachment support and a reusable reset mechanism to StreamingResponse, aligning the Python SDK’s streaming API with the .NET/C# SDK behavior for attachments and stream lifecycle reuse.

Changes:

• Introduces StreamingResponse.add_attachment() to append a single Attachment to the final streamed activity.
• Introduces StreamingResponse.reset() and extracts _initialize_state() to share initialization/reset logic.
• Adds tests validating attachment inclusion, accumulation, validation, and reset behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
libraries/microsoft-agents-hosting-core/microsoft_agents/hosting/core/app/streaming/streaming_response.py	Adds add_attachment() and reset(); refactors state initialization into _initialize_state() to support reuse.
tests/hosting_core/app/streaming/test_streaming_response.py	Adds new unit tests covering attachment behavior and reset semantics.

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[MattB (MattB-msft)]

Copilot Please run python black on the changes you have made

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

Copilot Please run python black on the changes you have made

Done — ran black on streaming_response.py in commit Apply Black formatting and fix _initialize_state to include _is_streaming_channel and _interval. This also fixed the missing blank line after reset() that the reviewer flagged, and I moved _is_streaming_channel and _interval into _initialize_state() so reset() fully restores those fields to baseline defaults before _set_defaults() re-applies channel-specific values.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.