feat(slack-gateway): add workspace synthetic tests

[onutc]

Summary

• add a browser-authenticated workspace test flow in the Slack gateway
• run synthetic Slack events through the existing routing/runtime pipeline with dry-run or real-reply modes
• mark synthetic prompts in the channel context and cover the new path with gateway tests

Testing

• go test ./... (in integrations/slack-gateway)

[gitrank-connector]

👍 GitRank PR Analysis

Score: 5 points

Metric	Value
Component	Other (1× multiplier)
Severity	P3 - Low (5 base pts)
Final Score	5 × 1 = 5

Eligibility Checks

Check	Status
Issue/Bug Fix	❌
Fix Implementation	✅
PR Documented	✅
Tests	✅
Lines Within Limit	✅

Impact Summary

This PR introduces synthetic test message functionality to the Slack gateway, allowing authenticated users to send test prompts through the existing routing pipeline in either dry-run or real-reply modes. The implementation adds a new HTTP endpoint (/slack/workspaces/test), supporting UI form, message event inference, and result tracking. The feature includes comprehensive test coverage with 4 new test cases validating authentication, form rendering, dry-run behavior, and real message posting.

Analysis Details

Component Classification: This PR adds a new feature (workspace synthetic tests) to the Slack gateway integration rather than fixing a specific categorized component. It falls under 'Other' as a miscellaneous feature addition.

Severity Justification: This is a low-severity contribution as it adds a testing/diagnostic feature for workspace management rather than fixing critical bugs or security issues. The feature enables developers to test Slack event routing but doesn't address production failures or data loss.

Eligibility Notes: Issue: False - no bug fix or issue resolution mentioned. Fix_implementation: True - PR delivers exactly what title describes (workspace synthetic tests). PR_linked: True - clear summary and testing instructions provided. Tests: True - 407 lines of test code added in gateway_test.go plus new test file. Tests_required: True - new feature adding business logic (message processing with options, synthetic event handling) requires comprehensive test coverage to ensure correctness of routing and delivery behavior.

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