fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts by chechunhsu · Pull Request #292 · vercel/chat

chechunhsu · 2026-03-24T01:18:44Z

Summary

Fixes #268

The empty threadTs for top-level DMs was intentionally added in #39 so that openDM() subscriptions match incoming DM messages. The previous approach of changing the threadTs logic to event.thread_ts || event.ts fixed the API error but broke subscription matching — DMs routed to onNewMention() instead of onSubscribedMessage().

This PR takes the two-part approach suggested in review feedback: preserve the empty threadTs for DM subscription matching, and guard Slack API calls so empty strings don't cause invalid_thread_ts errors.

What changed

Each method that calls Slack APIs (postMessage, postEphemeral, scheduleMessage, stream) now normalizes threadTs at entry:

const { channel, threadTs: rawThreadTs } = this.decodeThreadId(threadId);
const threadTs = rawThreadTs || undefined;

This follows the same pattern postEphemeral already used (thread_ts: threadTs || undefined), but applied once at method entry instead of at each call site.

Result

openDM() subscription matching continues to work (empty threadTs in threadId)
Slack API calls receive undefined instead of "" → no invalid_thread_ts errors
No behavioral change for channel messages or DM thread replies

Test plan

pnpm test --filter=@chat-adapter/slack — 297 tests pass
pnpm test --filter=@chat-adapter/integration-tests — replay-dm.test.ts 17 tests pass (DM subscription matching verified)
pnpm turbo build --filter=@chat-adapter/slack — builds cleanly with no type errors

vercel · 2026-03-24T01:18:49Z

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Additional Suggestion:

Test description claims "top-level DM messages use empty threadTs (matches openDM subscriptions)" but the test assertion expects a non-empty threadTs using event.ts, contradicting the description.

bensabic · 2026-03-31T11:41:18Z

Thanks for the fix, the invalid_thread_ts bug is definitely real and needs to be addressed.

However, the empty threadTs for top-level DMs was intentional (added in #39) so that openDM() subscriptions would match incoming DM messages. This PR fixes the API error but breaks that subscription matching, DMs now route to onNewMention() instead of onSubscribedMessage(), which is a regression for apps using openDM().

The issue author actually suggested a two-part fix: use event.ts as the fallback and guard the API calls with thread_ts: threadTs || undefined (like postEphemeral already does). Could we take that approach instead? That way postMessage/chatStream won't choke on empty threadTs, and openDM() subscription matching continues to work.

chechunhsu · 2026-04-01T02:25:20Z

Thanks for the detailed feedback! You're right — the empty threadTs for top-level DMs is intentional for openDM() subscription matching, and my original approach broke that.

I've updated the PR to take the two-part approach you suggested: keep the existing DM threadTs logic unchanged, and guard the Slack API calls against empty strings instead.

Specifically, each method that calls Slack APIs (postMessage, postEphemeral, scheduleMessage, stream) now normalizes threadTs at entry:

const { channel, threadTs: rawThreadTs } = this.decodeThreadId(threadId);
const threadTs = rawThreadTs || undefined;

This follows the pattern postEphemeral already used, but applied once per method rather than at each call site. All existing tests pass, including the DM subscription matching tests in replay-dm.test.ts.

bensabic · 2026-04-01T03:53:32Z

Thanks for the updated approach, guarding with rawThreadTs || undefined instead of changing how threadTs is computed is the right call. It preserves openDM() subscription matching while fixing the API errors.

Two things on the as string casts:

startTyping (line 2898): This one is fine since there's already an early return on if (!threadTs) above it. The cast is redundant though, you could drop it.
chatStream (line 2944): This one is unsafe. There's no guard, so if threadTs is undefined, it passes undefined to chat.startStream which requires thread_ts: string. That's exactly the invalid_arguments error from DMs broken: empty threadTs causes invalid_thread_ts and invalid_arguments #268. It probably can't happen in practice today (streaming is triggered from incoming messages which always have a valid event.ts), but the cast silences TypeScript rather than handling the case. Could you add the same guard that startTyping has, early return or fallback when threadTs is undefined?

…id_thread_ts Preserve the intentional empty threadTs for top-level DMs (added in vercel#39 for openDM() subscription matching) while preventing Slack API errors. Instead of changing the threadTs logic, normalize empty threadTs to undefined at the entry of each method that calls Slack APIs (postMessage, postEphemeral, scheduleMessage, stream). This way: - openDM() subscription matching continues to work (empty threadTs) - Slack API calls receive undefined instead of "" (no invalid_thread_ts) The stream method throws ValidationError on empty threadTs (matching startTyping's early-return pattern) so TypeScript narrows correctly without any `as string` casts. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

chechunhsu · 2026-04-01T08:48:22Z

Updated:

startTyping: Removed the redundant as string cast — TypeScript already narrows after the if (!threadTs) guard.
stream: Added a ValidationError guard when threadTs is empty (matching startTyping's pattern), so chatStream receives a properly narrowed string — no more as string cast.

Zero as string casts remaining.

…, and postEphemeral

vercel · 2026-04-06T18:13:28Z

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, Comment, Open in v0	Apr 6, 2026 6:14pm
chat-sdk-nextjs-chat	Ready	Preview, Comment, Open in v0	Apr 6, 2026 6:14pm

…id_thread_ts (vercel#292) * fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts Preserve the intentional empty threadTs for top-level DMs (added in vercel#39 for openDM() subscription matching) while preventing Slack API errors. Instead of changing the threadTs logic, normalize empty threadTs to undefined at the entry of each method that calls Slack APIs (postMessage, postEphemeral, scheduleMessage, stream). This way: - openDM() subscription matching continues to work (empty threadTs) - Slack API calls receive undefined instead of "" (no invalid_thread_ts) The stream method throws ValidationError on empty threadTs (matching startTyping's early-return pattern) so TypeScript narrows correctly without any `as string` casts. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> * Add tests for empty threadTs normalization in stream, scheduleMessage, and postEphemeral --------- Co-authored-by: Ben Sabic <bensabic@users.noreply.github.com>

…id_thread_ts (#292) * fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts Preserve the intentional empty threadTs for top-level DMs (added in #39 for openDM() subscription matching) while preventing Slack API errors. Instead of changing the threadTs logic, normalize empty threadTs to undefined at the entry of each method that calls Slack APIs (postMessage, postEphemeral, scheduleMessage, stream). This way: - openDM() subscription matching continues to work (empty threadTs) - Slack API calls receive undefined instead of "" (no invalid_thread_ts) The stream method throws ValidationError on empty threadTs (matching startTyping's early-return pattern) so TypeScript narrows correctly without any `as string` casts. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> * Add tests for empty threadTs normalization in stream, scheduleMessage, and postEphemeral --------- Co-authored-by: Ben Sabic <bensabic@users.noreply.github.com>

Bundles 5 small upstream bug fixes into one PR. Each is independent and covered by a regression test. - vercel/chat#394 (slack): preserve email addresses in @mention regex. ``user@domain.com`` no longer extracts ``@domain`` as a mention. - vercel/chat#292 (slack): guard Slack API calls against empty ``thread_ts`` to fix ``invalid_thread_ts`` errors. - vercel/chat#256 (discord): remove duplicate text when posting card messages. ``content`` is omitted on the create path and explicitly cleared on the edit path (Discord PATCH preserves omitted fields). - vercel/chat#395 (slack): enrich link previews with unfurl metadata from attachments. Routes ``message_changed`` events through a new ``_handle_message_changed`` so the message handler sees unfurled links instead of bare URLs. New cache + poll window. - vercel/chat#407 (telegram): rewrite format converter to emit MarkdownV2 (``*bold*`` etc.) instead of legacy ``Markdown``. Adds proper escaping for the 18 special characters MarkdownV2 reserves in normal text, the narrower set inside code blocks, and the parens/backslash escape inside link URLs. https://claude.ai/code/session_01FyMxQn2BEAzmwKS1GZczKj

#94) The vercel/chat#292 empty-thread_ts guard correctly avoided chat.startStream's invalid_thread_ts rejection, but raising ValidationError silently dropped top-level Slack DM streaming replies because Thread._handle_stream does not catch and _fallback_stream only triggers when the adapter has no stream method at all. Replace the raise with the production-tested accumulate-and-post path Tony described in chat-sdk-python#94: degrade DMs to a single non-streamed post_message call (Slack accepts an empty thread_ts on chat.postMessage) and keep native streaming for channels. This lets chinchill-api retire its MultiTenantSlackAdapter subclass override.

vercel Bot reviewed Mar 24, 2026

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chechunhsu force-pushed the fix/slack-dm-thread-ts branch from 30d48d8 to a6601ca Compare April 1, 2026 02:20

chechunhsu changed the title ~~fix(slack): use event.ts as threadTs fallback for DMs~~ fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts Apr 1, 2026

chechunhsu force-pushed the fix/slack-dm-thread-ts branch from a6601ca to 6570e06 Compare April 1, 2026 08:45

Add tests for empty threadTs normalization in stream, scheduleMessage…

70d952d

…, and postEphemeral

vercel Bot deployed to Preview – chat-sdk-nextjs-chat April 6, 2026 18:14 View deployment

vercel Bot deployed to Preview – chat April 6, 2026 18:14 View deployment

dancer approved these changes Apr 17, 2026

View reviewed changes

dancer merged commit 53c6b68 into vercel:main Apr 17, 2026
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dancer mentioned this pull request Apr 17, 2026

DMs broken: empty threadTs causes invalid_thread_ts and invalid_arguments #268

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patrick-chinchill mentioned this pull request May 9, 2026

fix(adapters): bug-fix sweep from upstream 4.27.0 (slack/discord/telegram) Chinchill-AI/chat-sdk-python#89

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vstratful mentioned this pull request May 14, 2026

Slack: support streaming replies to top-level message.im using incoming message ts #503

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fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts#292

fix(slack): guard Slack API calls against empty threadTs to fix invalid_thread_ts#292
dancer merged 2 commits into
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chechunhsu:fix/slack-dm-thread-ts

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