fix: Add CancellationToken to Slack and remove unused IHttpClientFactory

[thomhurst]

Summary

• Added CancellationToken parameter to ISlack.PostWebHookMessage for proper cancellation support
• Removed unused IHttpClientFactory parameter from Http.cs constructor

Changes

• ISlack.cs: Added optional CancellationToken parameter to PostWebHookMessage
• Slack.cs: Implemented cancellation token check in PostWebHookMessage
• Http.cs: Removed unused IHttpClientFactory from constructor

Fixes #1547, Fixes #1583

Test plan

• Build succeeds
• Existing tests pass

🤖 Generated with Claude Code

[thomhurst]

Summary

This PR adds CancellationToken support to the Slack webhook method and removes an unused IHttpClientFactory parameter from the Http class constructor.

Critical Issues

1. Incomplete CancellationToken implementation in Slack.PostWebHookMessage ⚠️

The PR adds a cancellationToken parameter and calls ThrowIfCancellationRequested() before creating the SlackClient, but the token is never passed to the actual slackClient.PostAsync() call:

public async Task PostWebHookMessage(SlackWebHookOptions options, CancellationToken cancellationToken = default)
{
    cancellationToken.ThrowIfCancellationRequested();
    
    var slackClient = new SlackClient(options.WebHookUri.AbsoluteUri, httpClient: _http.GetLoggingHttpClient());
    
    await slackClient.PostAsync(options.SlackMessage);  // ❌ Missing cancellationToken
}

This means:

• The method will only check cancellation before making the HTTP request
• The actual HTTP call to Slack cannot be cancelled once started
• This defeats the purpose of adding CancellationToken support

Expected fix:
Check if the SlackClient.PostAsync() method supports a CancellationToken parameter. If it does, pass it:

await slackClient.PostAsync(options.SlackMessage, cancellationToken);

If the Slack.Webhooks library doesn't support cancellation tokens in PostAsync, then:

• Either remove the early ThrowIfCancellationRequested() check (since it provides minimal value)
• Or document this limitation in a comment explaining that cancellation only works before the HTTP call begins

Suggestions

IHttpClientFactory removal looks correct ✅

The Http constructor parameter removal appears valid since:

• The parameter was never assigned to a field
• It's not used anywhere in the class
• The class creates its own ServiceProvider with HttpClient internally (line 97-100 in Http.cs)

However, verify that:

• All DI registrations were updated (no compilation errors)
• The Http class is still properly instantiated throughout the codebase

Previous Review Status

Unable to access previous comments due to GitHub token scope limitations.

Verdict

⚠️ REQUEST CHANGES - The CancellationToken is not passed to the underlying async operation, making the implementation incomplete and potentially misleading.