[adampeterhiggins]

There was no way to give an agent a Slack discussion without copying and pasting it. A Slack message can now be attached the same way a Linear issue or pull request is:

• Paste or type a permalink into the web or desktop composer. It becomes a #channel · Author chip once the thread loads. A reply, or a message with replies, brings its whole thread, with the linked message marked. Channel links stay as links. The first time a link can't be read because Slack isn't connected, a notice explains why.
• Paperclip → Slack message, or Attach Slack message in the command palette, opens a picker that uses Slack's search syntax (in:#eng from:@priya). Right-click a result and choose Attach only this message to leave out the rest of its thread.
• # menu: a Slack tab beside Pull requests, Linear, GitHub issues and Repositories. It appears once Slack is connected and only searches while it's visible.
• Mobile: chips render, the context sheet shows the snapshot with Open in Slack, and the attach menu has a Slack picker sheet. Mobile never turns pasted links into chips, so it has no paste case.

How it works

• Server (apps/server/src/slack/)
  • Reads Slack with the user's own token (read-only user scopes): search.messages, conversations.replies/info and users.info.
  • Saves the thread as capped markdown when it is attached. That markdown always keeps the first message and the linked one, fills the rest newest first, and resolves <@U…> mentions and channel links. Files are listed by name, not downloaded.
  • The snapshot is a new slack-thread context record, and every provider gets it in the prompt like Linear and GitHub issues.
• Auth (SlackAuth.ts) works like LinearAuth.
  • It uses PKCE with no client secret, which Slack has supported since March 2026.
  • The redirect lands on a fixed loopback port at http://localhost:47832/callback. Slack only treats localhost as a desktop redirect, not 127.0.0.1.
  • Remote browsers paste the redirect URL back.
  • Tokens without expires_in are kept as non-expiring; rotating tokens are refreshed.
• No built-in Slack app. Slack limits apps distributed to other workspaces without Marketplace approval to 1 thread read a minute, 15 messages each, which breaks thread attachments. Apps used only in the workspace that made them keep normal limits. So Settings → Integrations → Slack has Copy manifest: read scopes, the redirect, and pkce_enabled. The user creates the app at api.slack.com/apps and pastes its client ID. The server keeps that client ID across disconnects, and T3CODE_SLACK_CLIENT_ID can supply one.

Docs: new docs/user/slack.md, plus updates to composer.md and fork-differences.md.

Testing

• New tests: OAuth helpers, auth (no client ID configured, pasted-redirect login, disconnect keeps the client ID, refresh), the Web API wrapper (labels, thread_ts taken from permalinks, thread vs. single message, a reply link without thread_ts, not-found, revoked), markdown rendering, permalink parsing, the context record round-trip, and the prompt payload. All pass.
• Typecheck passes for server, web, mobile, contracts, client-runtime and shared.
• Not yet run against a real Slack workspace or in a client. Screenshots of the chip, picker and settings are still to come.
• One server.test.ts case ("flushes more than one tool chunk before the synchronization marker") fails the same way without this change.

🤖 Generated with Claude Code