Add proactive threading support

[corinagum]

Summary

• Add Reply() overloads on App for proactive thread sends (generic, string, AdaptiveCard — 2-arg and 3-arg forms)
• Add Conversation.ToThreadedConversationId() for constructing threaded conversation IDs
• supportsThreading inline check covers channels (@thread.tacv2/@thread.skype) and 1:1 (@unq.gbl.spaces)
• Update Context.Send() and Context.Reply() doc comments
• Add threading sample

Test plan

• Unit tests for ToThreadedConversationId() (10 tests) and Reply() (3 tests)
• E2E: All commands tested in 1:1 and channel (top-level + existing thread)
• dotnet build 0 errors, dotnet test all passed

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds proactive threading utilities and sample usage to enable replying/sending into Microsoft Teams channel threads (and certain 1:1 conversation IDs), with accompanying tests and updated docs.

Changes:

• Added App.Reply() proactive overloads (2-arg and 3-arg forms) and updated App.Send() docs/behavior.
• Added Conversation.ToThreadId() helper plus unit tests.
• Introduced a new Samples.Threading sample project demonstrating threading behaviors.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Tests/Microsoft.Teams.Apps.Tests/AppTests.cs	Adds unit tests validating App.Reply() thread-id construction and invalid message-id handling.
Tests/Microsoft.Teams.Api.Tests/ConversationTests.cs	Adds unit tests for Conversation.ToThreadId() formatting and validation behavior.
Libraries/Microsoft.Teams.Apps/Contexts/Context.Send.cs	Updates XML docs clarifying Send() vs Reply() quoting/threading behavior.
Libraries/Microsoft.Teams.Apps/App.cs	Adds proactive Reply() overloads; adjusts proactive Send() docs and how Conversation.Type is populated.
Libraries/Microsoft.Teams.Api/Conversation.cs	Adds Conversation.ToThreadId() helper and validation.
Samples/Samples.Threading/*	Adds a new sample project (README, Program, appsettings, csproj) demonstrating threading scenarios.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

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