[BUG] Fix Type Error in Slack postReplyInThread Method #3895

Describe the bug.

The postReplyInThread method in netlify/functions/save-discussion-background/Slack.ts has a TypeScript error due to incompatible types in the Slack Web API call:

Argument of type '{ channel: string; text: string; as_user: true; thread_ts: string; icon_url: string; }' is not assignable to parameter of type 'ChatPostMessageArguments'.
  Types of property 'icon_url' are incompatible.
    Type 'string' is not assignable to type 'undefined'.

Current Behavior

• When posting a reply in a Slack thread, we're trying to set both as_user: true and icon_url
• This causes a type error because when posting as a user (as_user: true), Slack automatically uses the user's profile picture
• The code currently attempts to override this with a custom icon URL, which is not allowed by the API

Expected behavior

• Messages should be posted as the authenticated user with their profile picture
• No type errors in the TypeScript compilation

Screenshots

How to Reproduce

View Error:

# Run TypeScript check on the specific file
npx tsc netlify/functions/save-discussion-background/Slack.ts --noEmit

The type error will appear:

Error: Argument of type '{ channel: string; text: string; as_user: true; thread_ts: string; icon_url: string; }' is not assignable to parameter of type 'ChatPostMessageArguments'.
Types of property 'icon_url' are incompatible.
 Type 'string' is not assignable to type 'never'.

🥦 Browser

None

👀 Have you checked for similar open issues?

• I checked and didn't find similar issue

🏢 Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

Are you willing to work on this issue ?

Yes I am willing to submit a PR!