v0.4.29

Synced to upstream Vercel Chat v4.29.0 (release commit 6581d31; UPSTREAM_PARITY = "4.29.0"). Upstream never tagged chat@4.27.0/chat@4.28.0.

Highlights

• Meta Messenger adapter — the 9th platform
• chat/ai tool factories (create_chat_tools)
• callback_url on buttons and modals (vercel/chat#454)
• Transcripts API + per-thread cache rename message_history → thread_history (vercel/chat#448), with back-compat shims at the old import path and config names
• message.subject + fetch_subject adapter hook (#131)
• Slack feature wave — verifier precedence flip, external installation providers, native markdown_text, web_client property (#127), and a DM block-action threading fix (#137)
• Teams outbound files via data-URI activity attachments (#125)
• Upstream adapter-hardening security pass (SSRF/URL-allowlist, fail-closed verification)
• burst concurrency strategy

⚠️ Breaking changes

• Python floor raised to 3.12 (was 3.10) — required for the Teams SDK migration line.
• Google Chat fail-closed JWT verification at construction (#130, port of upstream 9824d33): GoogleChatAdapter.__init__ now raises ValidationError unless one of google_chat_project_number, pubsub_audience, or disable_signature_verification is set (config or GOOGLE_CHAT_* env). Existing gchat deployments must set one of these.

Deferred to 0.4.29.1

• Google Chat multipart file upload (#112) — pending the /attachments:upload endpoint + media-scope fixes.
• Teams content.downloadUrl surfacing (#136) — pending a one-line is not None guideline fix.

See CHANGELOG.md for the complete list of ports and Python-only divergences (docs/UPSTREAM_SYNC.md).