docs(sync): tick CHANGELOG checkboxes + document Teams SDK 2.0.8 N/A

Final upstream-coverage audit before merging the 7 sync PRs (#84-#90)
identified one undocumented N/A item:

vercel/chat#415 (Teams SDK 2.0.8 + User-Agent) is a JS-only botbuilder
dependency bump. The Python Teams adapter uses raw aiohttp (no
botbuilder), so there is no equivalent dependency to bump. The optional
User-Agent: Vercel.ChatSDK header on the ~9 outbound aiohttp call sites
is a defense-in-depth nice-to-have; deferred as a follow-up rather than
landed in this sync.

Updates:
- CHANGELOG.md: tick all completed items and link them to their PRs
  (#84, #85, #86, #87, #88, #89, #90, plus already-merged PR #74).
  Document #415 inline as N/A.
- docs/UPSTREAM_SYNC.md non-parity table: add row for Teams User-Agent
  header divergence so future syncers don't try to "port" the JS bump.

Item #6 (concurrency.maxConcurrent) is already implementation-covered
in the Python port (existing divergence row at L492). The 4 new TS
concurrency tests in chat.test.ts have Python-specific equivalents at
test_chat_faithful.py L2969-3055 that don't name-match — leaving as
deferred fidelity-baseline polish since the behavior is verified.

Verdict from the coverage audit: all 18 substantive ports across PRs
#84-#90 are upstream-verified. No commits in chat@4.26.0..f55378a were
missed. Ready to start merging.

https://claude.ai/code/session_01FyMxQn2BEAzmwKS1GZczKj

Author: claude

CHANGELOG.md

@@ -26,36 +26,36 @@ intended in-flight signal.
 
 #### Core (`packages/chat/` → `src/chat_sdk/`)
 
-- [ ] **`chat.getUser(adapter, userId)`** for cross-platform user lookups (vercel/chat#391, upstream commit `a520797`). Adapter-side: each adapter exposes `getUser`. Touches `chat.py`, `types.py` (`User` type extension), and every adapter (`slack`, `teams`, `gchat`, `telegram`, `discord`, `whatsapp`, `github`, `linear`).
-- [ ] **`ExternalSelect.initial_option` + `option_groups`** (vercel/chat#410, `70281dc`). Type extension in `types.py`; Slack adapter must serialize `option_groups` to Block Kit.
-- [ ] **`thread.post()` streaming options** (vercel/chat#388, `9093292`). New params plumb through `Thread.post` → `chat.py` orchestrator.
-- [ ] **Slack streaming team ID fix for interactive payloads** (vercel/chat#330, `8a0c7b3`). Bug fix in the Slack streaming path; check `adapters/slack/adapter.py` request-context plumbing.
-- [ ] **Bundled guide markdown + templates manifest** (vercel/chat#423, `b0ab804`). Decision: skip or copy `packages/chat/resources/guides/*.md` and `templates.json` verbatim. Probably skip — these are TS-monorepo authoring resources, not runtime behavior.
+- [x] (PR #90) **`chat.getUser(adapter, userId)`** for cross-platform user lookups (vercel/chat#391, upstream commit `a520797`). Adapter-side: each adapter exposes `getUser`. Touches `chat.py`, `types.py` (`User` type extension), and every adapter (`slack`, `teams`, `gchat`, `telegram`, `discord`, `whatsapp`, `github`, `linear`).
+- [x] (PR #84) **`ExternalSelect.initial_option` + `option_groups`** (vercel/chat#410, `70281dc`). Type extension in `types.py`; Slack adapter must serialize `option_groups` to Block Kit.
+- [x] (already merged via PR #74) **`thread.post()` streaming options** (vercel/chat#388, `9093292`). New params plumb through `Thread.post` → `chat.py` orchestrator.
+- [x] (PR #85) **Slack streaming team ID fix for interactive payloads** (vercel/chat#330, `8a0c7b3`). Bug fix in the Slack streaming path; check `adapters/slack/adapter.py` request-context plumbing.
+- [⏭️] (out of scope) **Bundled guide markdown + templates manifest** (vercel/chat#423, `b0ab804`). Decision: skip or copy `packages/chat/resources/guides/*.md` and `templates.json` verbatim. Probably skip — these are TS-monorepo authoring resources, not runtime behavior.
 - [x] **`concurrency.maxConcurrent` honored in `concurrent` strategy** (vercel/chat#419, `d630e6c`). Already addressed in the Python port — see the existing `ConcurrencyConfig.max_concurrent` row in `docs/UPSTREAM_SYNC.md` (we enforce via `asyncio.Semaphore` and reject misconfiguration). Upstream has now caught up; on this sync the divergence row downgrades from "silent correctness bug upstream" to "behavior parity restored".
 
 #### Slack (`packages/adapter-slack/` → `src/chat_sdk/adapters/slack/`)
 
-- [ ] **Slack Socket Mode support** (vercel/chat#162, `7e9d0fc`). Big — adds a persistent WebSocket transport alongside HTTP webhooks. Decision: in scope or follow-up? Mirrors the Discord Gateway gap already documented in non-parity ("HTTP interactions only").
-- [ ] **Dynamic `bot_token` resolver + custom `webhookVerifier`** (vercel/chat#421, `2531e9c`). Multi-workspace pattern; touches `SlackAdapter.__init__` and request handling.
-- [ ] **External-select Block Kit support** (vercel/chat#397, `a179b29`). Pairs with the core `option_groups` change above.
+- [x] (PR #86) **Slack Socket Mode support** (vercel/chat#162, `7e9d0fc`). Big — adds a persistent WebSocket transport alongside HTTP webhooks. Decision: in scope or follow-up? Mirrors the Discord Gateway gap already documented in non-parity ("HTTP interactions only").
+- [x] (PR #87) **Dynamic `bot_token` resolver + custom `webhookVerifier`** (vercel/chat#421, `2531e9c`). Multi-workspace pattern; touches `SlackAdapter.__init__` and request handling.
+- [x] (PR #84) **External-select Block Kit support** (vercel/chat#397, `a179b29`). Pairs with the core `option_groups` change above.
 - [ ] **Native `markdown_text` for outgoing messages** (vercel/chat#440, post-release — Apr 17). NOTE: this commit is post-`f55378a` so technically out of `4.27.0` scope, but listed here because the team often picks up post-release fixes.
-- [ ] **Link-preview unfurl metadata enrichment** (vercel/chat#395, `ded6f78`).
-- [ ] **`@mention` regex preserves email addresses** (vercel/chat#394, `c26ee6c`).
-- [ ] **Guard against empty `threadTs` (`invalid_thread_ts` fix)** (vercel/chat#292, `53c6b68`).
+- [x] (PR #89) **Link-preview unfurl metadata enrichment** (vercel/chat#395, `ded6f78`).
+- [x] (PR #89) **`@mention` regex preserves email addresses** (vercel/chat#394, `c26ee6c`).
+- [x] (PR #89) **Guard against empty `threadTs` (`invalid_thread_ts` fix)** (vercel/chat#292, `53c6b68`).
 
 #### Teams (`packages/adapter-teams/` → `src/chat_sdk/adapters/teams/`)
 
-- [ ] **Native streaming for DMs via `emit`** (vercel/chat#416, `ed46bae`). Currently the Python port falls back to `_fallback_stream` for Teams; native streaming would lift that.
-- [ ] **DM conversation ID resolution for Graph API** (vercel/chat#403, `4c24c94`). Bug fix.
-- [ ] **Teams SDK 2.0.8 + `User-Agent` header** (vercel/chat#415, `885a471`). TS-side dependency bump; Python equivalent is to verify our `botbuilder` pin and propagate `User-Agent` if not already.
+- [x] (PR #88) **Native streaming for DMs via `emit`** (vercel/chat#416, `ed46bae`). Currently the Python port falls back to `_fallback_stream` for Teams; native streaming would lift that.
+- [x] (PR #85) **DM conversation ID resolution for Graph API** (vercel/chat#403, `4c24c94`). Bug fix.
+- [x] **Teams SDK 2.0.8 + `User-Agent` header** (vercel/chat#415, `885a471`). **N/A — JS-only.** Upstream's change bumps the `botbuilder` dependency and flips the bot client header from `X-User-Agent` to `User-Agent: Vercel.ChatSDK`. The Python Teams adapter does not depend on `botbuilder` (uses raw `aiohttp`), so there is no equivalent dependency to bump. The optional `User-Agent` header propagation is a defense-in-depth nice-to-have; documented as a deferred enhancement in `docs/UPSTREAM_SYNC.md` rather than landed in this sync.
 
 #### Telegram
 
-- [ ] **MarkdownV2 rendering fixes** (vercel/chat#407, `b9a1961`). Pairs with the streaming-chunk safety trim in vercel/chat#446 (post-`f55378a`).
+- [x] (PR #89) **MarkdownV2 rendering fixes** (vercel/chat#407, `b9a1961`). Pairs with the streaming-chunk safety trim in vercel/chat#446 (post-`f55378a`).
 
 #### Discord
 
-- [ ] **Don't duplicate text when posting card messages** (vercel/chat#256, `7e5b447`). Confirm Python port's `discord/cards.py` doesn't have the same bug.
+- [x] (PR #89) **Don't duplicate text when posting card messages** (vercel/chat#256, `7e5b447`). Confirm Python port's `discord/cards.py` doesn't have the same bug.
 
 #### Out of scope for this Python port
 

docs/UPSTREAM_SYNC.md

@@ -503,6 +503,7 @@ stay explicit instead of being rediscovered in code review.
 | Teams `dialog_open_timeout_ms` config | Not implemented | Configurable | Low demand |
 | Google Chat file uploads | Ignored in message parse | Supported | API complexity; can add later |
 | Discord Gateway WebSocket | HTTP interactions only | Both HTTP and Gateway | Gateway requires persistent connection |
+| Teams `User-Agent: Vercel.ChatSDK` outbound header | Not set on `aiohttp` calls | Propagated by `botbuilder` 2.0.8 | Python Teams adapter doesn't use `botbuilder` (raw `aiohttp`). Upstream's vercel/chat#415 was a JS-only `botbuilder` SDK bump that flipped `X-User-Agent` → `User-Agent`. No equivalent dependency to bump on the Python side. Setting a `User-Agent` on the ~9 outbound `aiohttp` call sites would be a defense-in-depth nice-to-have; deferred to a follow-up. |
 
 ### Serialization differences