Preserve textFormat through HttpStream's intermediate and final activities

[Copilot]

Summary

HttpStream rebuilds outbound activities on every flush/close and forwarded the last emitted message's attachments, entities, suggested actions, and channelData — but not textFormat. As a result, stream.emit({ text, textFormat: 'extendedmarkdown' }) was accepted but dropped on every intermediate typing chunk and on the final message, so streamed Extended Markdown rendered as plain markdown.

Fix

• Model textFormat on ITypingActivity / ITypingActivityInput / TypingActivityInput with a withTextFormat() builder (mirroring MessageActivityInput).
• HttpStream reads the last emitted message's textFormat (same "last message wins" state as attachments/entities/etc.) and applies it to the cumulative typing chunks and informative updates in flush(), the final message in close(), and the timeout fallback in sendFinal().

Testing

• Unit tests in packages/api/src/activities/typing.spec.ts and packages/apps/src/http/http-stream.spec.ts covering textFormat on typing activities and propagation across intermediate chunks, the final message, and the timeout fallback.
• Validated live in Teams: with the fix, streamed task lists and strikethrough render correctly; without it they fall back to plain markdown.

Note on C#

This repo only contains the TypeScript SDK; the .NET streaming abstraction is out of scope here.

[Corina (corinagum)]

Kavin (@singhk97) Do we have confirmation from service team that typing activities are supposed to support textFormat? This is an alarming API change if so. Confirmed by Lily: https://learn.microsoft.com/en-us/microsoftteams/platform/bots/streaming-ux?tabs=csharp&pivots=teams-sdk-csharp#stream-message-through-rest-api

[Kavin (singhk97)]

Before fix:

before-fix.mp4

After fix:

after-fix.mp4

[Copilot]

Pull request overview

This PR fixes a streaming regression where HttpStream rebuilt intermediate/final activities without carrying forward the last emitted message’s textFormat, causing streamed Extended Markdown to render as plain markdown. It extends typing activity models/builders to support textFormat, and ensures HttpStream propagates that value consistently across intermediate typing chunks, final close, and timeout fallback.

Changes:

• Add textFormat support (and withTextFormat() builder) to typing activity interfaces and builders in @microsoft/teams.api.
• Update HttpStream to apply the last emitted message’s textFormat to intermediate typing chunks, the final message sent on close(), and the sendFinal() timeout fallback.
• Add unit tests covering typing textFormat modeling and end-to-end propagation through streaming behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/apps/src/http/http-stream.ts	Propagates finalActivity.textFormat into typing chunks and final/timeout message sends.
packages/apps/src/http/http-stream.spec.ts	Adds tests verifying textFormat is retained for intermediate chunks, final message, and timeout fallback.
packages/api/src/activities/typing.ts	Models textFormat on typing activities and adds withTextFormat() builders.
packages/api/src/activities/typing.spec.ts	Adds unit tests for TypingActivityInput and TypingActivity textFormat behavior.
examples/stream/src/index.ts	Extends the streaming example to demonstrate Extended Markdown deltas via textFormat: 'extendedmarkdown'.
examples/stream/README.md	Documents how to trigger the Extended Markdown streaming demo.

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