Sync upstream 4.28 + 4.29 (next sync after 4.27 wave lands)

[patrick-chinchill]

Background

Upstream has moved on while the 4.27.0 sync (PRs #83, #85, #86, #87, #88, #89, #90) was in flight:

• chat@4.28.0 — released between 4.27.0 (Apr 30) and 4.29.0 (May 18)
• chat@4.29.0 — released 2026-05-18

When the 4.27 sync wave lands, we'll be ~3 weeks behind upstream. This issue tracks the next sync to catch up to 4.29.0.

Headline items from 4.28 + 4.29

Core (packages/chat)

• New chat/ai subpath — createChatTools + toAiMessages for Vercel AI SDK integration. Substantial new public API surface; needs design discussion on the Python equivalent (do we plumb to Anthropic SDK / OpenAI SDK / something else?).
• Burst concurrency strategy — new option beyond the existing drop / queue / debounce / concurrent. Likely a moderate port; depends on the upstream semantics.

Adapters

• Adapter internals visibility: private → protected to enable subclassing. Python equivalent is a code-style audit — we use _underscore for protected; need to verify our subclass-ability matches upstream's new contract.
• @chat-adapter/telegram: improved attachment uploads + video note handling. Post-dates fix(telegram): MarkdownV2 rendering + telegram-chat reference example vercel/chat#407 (the MarkdownV2 fix already in fix(adapters): bug-fix sweep from upstream 4.27.0 (slack/discord/telegram) #89), so additive rather than conflicting.
• @chat-adapter/web: Vue + Svelte support. Out of scope for chat-sdk-python (no browser runtime).
• @chat-adapter/tests (new package): testing utilities for adapter authors. Maybe useful to mirror as a Python helper module, maybe not — we have our own pattern.

Config

• Configuration types reorganized for cross-package consistency, with backward-compatible deprecated aliases. Probably mechanical.

Teams adapter — migration window

Issue #93 (Teams adapter → microsoft-teams-apps Python SDK) is already tracked for 0.4.28. The natural cadence is:

• 0.4.27: ship the in-flight wave (hand-rolled streaming + bug fixes)
• 0.4.28 / 0.4.29: combined sync with the Teams SDK migration as the headline Teams change

This aligns nicely — the migration replaces our hand-rolled Bot Framework REST loop with the official SDK's ctx.stream.emit(), and lands inside the same release window as the upstream private → protected adapter visibility audit.

Suggested sync structure (mirroring 4.26 → 4.27 cadence)

1. Sync starter PR (alpha bump to 0.4.29a1, plan in CHANGELOG)
2. chat/ai subpath port (likely the biggest individual PR)
3. Burst concurrency strategy port
4. Adapter visibility audit (probably 1-2 lines per adapter)
5. Telegram attachment improvements (small additive)
6. Teams adapter migration to microsoft-teams-apps (issue Migrate Teams adapter to microsoft-teams-apps (official MS Python SDK) #93 — the headline Teams change)
7. Sync-completion PR (version bump to 0.4.29, fidelity check, CHANGELOG roll-up)

Out of scope

• @chat-adapter/web Vue/Svelte (no browser runtime in chat-sdk-python)
• @chat-adapter/tests package (re-evaluate — may or may not port)
• Vercel-specific release/CI automation (#520, #522, #524, #543, #544)

Acceptance criteria

• UPSTREAM_PARITY = "4.29.0" and version 0.4.29
• Lint workflow re-pinned from chat@4.27.0 to chat@4.29.0
• scripts/fidelity_baseline.json regenerated against 4.29.0
• All headline items above ported or explicitly documented as deferred in UPSTREAM_SYNC.md
• Teams SDK migration (Migrate Teams adapter to microsoft-teams-apps (official MS Python SDK) #93) lands within this sync (or has an explicit deferred-to-0.4.30 row if it slips)

References

• 4.29.0 release notes (latest tag as of 2026-05-18)
• Issue Migrate Teams adapter to microsoft-teams-apps (official MS Python SDK) #93 — Teams adapter migration to microsoft-teams-apps
• 4.27.0 sync wave: sync: upstream v4.27.0 (alpha 1) #83 (parent), fix(adapters): Slack streaming team_id + Teams DM Graph conversation IDs (vercel/chat#330, #403) #85, feat(slack): Socket Mode transport (vercel/chat#162) #86, feat(slack): dynamic bot_token resolver and custom webhook_verifier (vercel/chat#421) #87, feat(teams): native streaming for DMs via emit (vercel/chat#416) #88, fix(adapters): bug-fix sweep from upstream 4.27.0 (slack/discord/telegram) #89, feat(chat): add chat.get_user() for cross-platform user lookups (vercel/chat#391) #90