@mention autocomplete for connected MCP services (e.g. Slack users)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Most modern apps show a user picker when you type @ — Slack, Linear, Notion, GitHub itself. Claude Code's @ control doesn't do this. The current behavior (typing a name and letting the agent resolve it) works, but it's less business-user friendly: there's no visual roster, no confirmation you're targeting the right person, and it requires more keystrokes than it should.

Proposed Solution

When a user types @ in the Claude Code chat input, show an autocomplete dropdown populated from a locally cached roster of users/entities from connected MCPs (Slack, Linear, etc.). The cache could be built on first connection and refreshed periodically — no need to hit the API on every keystroke. Selecting an entry inserts a structured reference the agent can resolve unambiguously.

Claude Code + Slack MCP already supports sending messages, searching users, and posting to channels. An @mention picker would remove keystrokes, reduce ambiguity, and make the messaging workflow feel native — closer to typing in Slack itself.

Alternative Solutions

Currently, I just type first names and let the agent resolve them via the Slack MCP search API. It works, but there's no visual confirmation until after the agent has already composed the message.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

1. I'm using Claude Code with the Slack MCP connected
2. I want to send a message to a teammate named "Jesse"
3. 3. I type "send @" and an autocomplete dropdown appears showing my Slack workspace roster (cached locally)
4. 4. I select "Jesse Papocchia" from the dropdown — a structured reference is inserted
5. 5. I finish typing my message and the agent resolves the reference unambiguously, no API call needed for the lookup

Additional Context

_No response_