Slack: reaction events expose user IDs instead of display names

[akkadaska]

Bug Description

Slack onReaction events expose the reacting user as a raw Slack user ID in event.user.userName and event.user.fullName.

Incoming Slack messages and slash commands already resolve Slack user IDs to profile names through the adapter's cached user lookup path, but reaction events do not.

Steps to Reproduce

1. Configure the Slack adapter and register an onReaction handler.
2. Add a reaction to a Slack message that the app can receive through reaction_added events.
3. Inspect event.user.userName or event.user.fullName inside the handler.

Expected Behavior

event.user.userName should contain the Slack user's display name when available.

event.user.fullName should contain the Slack user's real name when available.

If Slack user lookup fails, both fields should fall back to the raw user ID.

Actual Behavior

event.user.userName and event.user.fullName are always set to the raw Slack user ID, for example U1234567890.

Code Sample

chat.onReaction(async (event) => {
  console.log(event.user.userId); // "U1234567890"
  console.log(event.user.userName); // Actual: "U1234567890"; Expected: "Alice"
  console.log(event.user.fullName); // Actual: "U1234567890"; Expected: "Alice Example"
});

Chat SDK Version

@chat-adapter/slack@4.26.0

Node.js Version

24.15.0

Platform Adapter

Slack

Operating System

macOS

Additional Context

No response