Teams: support microsoft-teams-apps 2.1 (activity_sender removal, activities update signature) #250

Summary

microsoft-teams-apps 2.1.0 (2026-09-16) broke the Teams adapter, so the SDK is now capped at <2.1 (see the linked PR). This issue covers adapting to 2.1 and lifting the cap.

What broke on 2.1.0

• App.activity_sender no longer exists. src/chat_sdk/adapters/teams/adapter.py:943 (self._app.activity_sender.create_stream(ref)) builds native DM streams through it. Failing tests: tests/test_teams_native_streaming.py::TestCreateStreamer::test_creates_streamer_for_valid_dm_activity and ::test_returns_none_when_create_stream_raises.
• The activities client's update signature changed (unexpected keyword argument), which breaks the service-URL retargeting in edit_message (_point_app_api_at, adapter.py:1413-1433). Failing test: tests/test_teams_adapter.py::TestOutboundServiceUrlRouting::test_edit_message_retargets_real_activities_client.

Scope

• Read the 2.1.0 changelog/source for the replacement streaming entry point and the new update signature.
• Support both 2.0.x and 2.1.x (feature-detect, don't version-sniff), or raise the floor to 2.1 if dual support is impractical. Document the choice.
• Lift the <2.1 cap in all three dependency lists in pyproject.toml.
• Run the full validation against both 2.0.16 and 2.1.x.
• Live Teams check of native DM streaming and edit-message before release.

Notes

• Related: [4.41/T4] Teams outbound: reactions, targeted ephemeral messages, placeholder-aware native streaming #219 (T4, Teams native streaming with placeholders) and [4.41/T1] Teams routing & outbound text: stop <at> rewriting, conversationType in thread ids, per-service-URL clients #216 (T1, per-service-URL clients) touch the same code paths. Coordinate, or land this first.
• uv.lock is gitignored, so dependency drift reaches CI and fresh installs directly. This has happened before (test(teams): make the skip-auth fixture survive the SDK's flag rename #180). Consider tighter upper bounds for fast-moving SDKs.

Part of #184.