Preserve textFormat through TeamsStreamingWriter's intermediate and final activities by Copilot · Pull Request #661 · microsoft/teams.net

Copilot · 2026-08-27T20:04:47Z

Summary

Mirrors microsoft/teams.ts#762, applied to the .NET streaming abstraction (TeamsStreamingWriter).

The .NET streamer has a different shape than the TS HttpStream (raw string deltas are accumulated via AppendResponseAsync, with a structured MessageActivityInput only supplied at FinalizeResponseAsync), so the bug shows up slightly differently here: StreamingActivityInput (the typing-type chunk used for informative/intermediate updates) never modeled textFormat at all, so there was no way to make intermediate streamed chunks render as anything other than the default format — only the final message (built directly from the caller-supplied MessageActivityInput) could carry it. In practice this meant content intended to stream as Extended Markdown (task lists, strikethrough, etc.) rendered as plain markdown while streaming and only switched format once the final message landed.

Fix

Modeled TextFormat on StreamingActivityInput (the typing-type chunk used for informative/intermediate updates), with a WithTextFormat() builder mirroring MessageActivityInput.
Added TeamsStreamingWriter.WithTextFormat(TextFormat): sets the format applied to every subsequent informative/intermediate typing chunk, and used as the final message's default format unless the caller sets TextFormat explicitly on the activity passed to FinalizeResponseAsync (explicit final value wins).
The tracked format resets when the writer is reused for a new streamed message after FinalizeResponseAsync, consistent with how the rest of the per-stream state (accumulated text, sequence, etc.) resets.

Note

Extended Markdown is available in public developer preview, which is why the corresponding TextFormats.ExtendedMarkdown constant remains behind the ExperimentalTeamsExtendedMarkdown diagnostic.

Testing

Added unit tests in TeamsStreamingWriterTests.cs covering: format applied to informative + streaming chunks + final message, no format sent when unset, explicit final-activity format overriding the writer's tracked format, and reset on stream reuse.
Full Microsoft.Teams.Apps.UnitTests suite passes (532/532).

Created from a Microsoft Teams conversation.

I attest that I have verified

…inal activities Mirrors microsoft/teams.ts PR #762 for the .NET streaming writer. - StreamingActivityInput (the typing-type chunks used for informative and intermediate streaming updates) now models textFormat and gets a WithTextFormat builder method, matching MessageActivityInput. - TeamsStreamingWriter.WithTextFormat(TextFormat) sets the format applied to every subsequent intermediate chunk, and is used as the final message's default format unless the caller sets TextFormat explicitly on the activity passed to FinalizeResponseAsync. - The tracked format resets when the writer is reused for a new streamed message after finalize, matching how other per-stream state is reset. Without this, streamed extended markdown content (task lists, strikethrough, etc.) rendered as plain markdown during intermediate typing chunks and only switched to the intended format on the final message. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

azure-pipelines · 2026-08-27T20:04:56Z

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Kavin (singhk97) · 2026-08-27T20:41:36Z

After fix demo:

after-fix-cs.mp4

Copilot

Pull request overview

This PR fixes a formatting inconsistency in TeamsStreamingWriter so that TextFormat (notably Extended Markdown) is preserved across intermediate “typing” chunks and the final message, rather than only being applied at finalize time.

Changes:

Adds TextFormat support to StreamingActivityInput plus a fluent WithTextFormat() builder API.
Adds TeamsStreamingWriter.WithTextFormat(TextFormat) to track/apply a per-stream format to informative + streaming chunks, and as the default for the final message unless explicitly overridden.
Adds unit tests covering propagation, unset behavior, final override precedence, and state reset on writer reuse.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
test/Microsoft.Teams.Apps.UnitTests/TeamsStreamingWriterTests.cs	Adds coverage for `TextFormat` propagation/override/reset behaviors in streaming.
src/Microsoft.Teams.Apps/TeamsStreamingWriter.cs	Tracks a per-stream `TextFormat` and applies it to intermediate chunks and (as a default) to the final message.
src/Microsoft.Teams.Apps/TeamsStreamingWriter.Activity.cs	Models `textFormat` on `StreamingActivityInput` and exposes it via the builder.

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Mehak Bindra (MehakBindra) · 2026-08-28T22:54:26Z

+    /// Cleared when the stream is reused for a new streamed message after
+    /// <see cref="FinalizeResponseAsync"/>; call this again for each new streamed message.
+    /// </remarks>
+    public TeamsStreamingWriter WithTextFormat(TextFormat textFormat)


I feel like having this both in activity and writer is confusing, if both are filled, which one is honored? Let's just keep it contained to streaming activity?

Replace writer-level WithTextFormat with per-chunk overloads: - Add AppendResponseAsync(MessageActivityInput) honoring Text + TextFormat - Add SendInformativeUpdateAsync(string, TextFormat) for per-informative format - Track last-streamed format for the final message's default (explicit final wins) Also update the StreamingBot sample: make Azure OpenAI optional (canned streamed fallback when unconfigured), demonstrate the per-chunk API in the extended-markdown path, and simplify to a single 'extended markdown' command. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: bf9dec16-4ade-483a-b60f-88d651e345f4

Kavin (singhk97) · 2026-08-31T21:37:23Z

I attest that I have verified

Kavin (singhk97) · 2026-08-31T21:37:55Z

-      .AsIChatClient());
+// Azure OpenAI is optional. When all three settings are present the default message path streams
+// live model output; otherwise it falls back to a canned streamed response so the sample still runs.
+string? endpoint = builder.Configuration["AzureOpenAI:Endpoint"];


updated sample to not require aoai keys

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: bf9dec16-4ade-483a-b60f-88d651e345f4

Kavin (singhk97) · 2026-08-31T21:52:32Z

I attest that I have verified

Mehak Bindra (MehakBindra) · 2026-08-31T22:08:52Z

        _sequence++;
        _logger.LogDebug("Sending informative streaming update (sequence {Sequence}).", _sequence);
-        SendActivityResponse? response = await TrySendChunkAsync(BuildActivity(text, StreamTypes.Informative), cancellationToken).ConfigureAwait(false);
+        SendActivityResponse? response = await TrySendChunkAsync(BuildActivity(text, StreamTypes.Informative, textFormat), cancellationToken).ConfigureAwait(false);


TrySendChunkAsync doesn't seem modified

Copilot AI requested a lite review from Copilot and removed request for Copilot August 27, 2026 20:04

Corina (corinagum) approved these changes Aug 27, 2026

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Merge branch 'main' into copilot/preserve-textformat-streaming-writer

753c4a1

Copilot AI lite review requested due to automatic review settings August 28, 2026 22:49

Copilot started reviewing on behalf of Mehak Bindra (MehakBindra) August 28, 2026 22:50 View session

Copilot AI reviewed Aug 28, 2026

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Comment thread test/Microsoft.Teams.Apps.UnitTests/TeamsStreamingWriterTests.cs Outdated

Mehak Bindra (MehakBindra) reviewed Aug 28, 2026

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Mehak Bindra (MehakBindra) requested changes Aug 28, 2026

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Kavin (singhk97) mentioned this pull request Aug 31, 2026

fix(apps): source informative textFormat from the update + add textFormat to update() microsoft/teams.ts#784

Open

Kavin (singhk97) reviewed Aug 31, 2026

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chore: retrigger attestation build check

ecfb8fe

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: bf9dec16-4ade-483a-b60f-88d651e345f4

Merge branch 'main' into copilot/preserve-textformat-streaming-writer

47a05f9

Mehak Bindra (MehakBindra) reviewed Aug 31, 2026

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Preserve textFormat through TeamsStreamingWriter's intermediate and final activities - #661

Preserve textFormat through TeamsStreamingWriter's intermediate and final activities#661
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