fix: Add XSS protection to flow visualization (issue #4326)

[devin-ai-integration]

fix: Add XSS protection to flow visualization (issue #4326)

Summary

This PR addresses a potential XSS vulnerability in the flow visualization component (interactive.js) as reported in issue #4326. The visualization uses innerHTML to render drawer content including source code and metadata, which could originate from AI agent outputs.

Changes:

• Added DOMPurify library (v3.0.6) via CDN for HTML sanitization
• Created escapeHtml() helper function to escape user-controlled text values
• Created sanitizeHtml() function using DOMPurify with an allowlist of safe tags/attributes
• Applied sanitizeHtml() to drawer content before setting innerHTML
• Applied escapeHtml() to user-controlled values in renderTriggerCondition, renderConditionTree, and renderMetadata methods
• Added 4 tests to verify XSS protection is in place

Review & Testing Checklist for Human

• Verify the DOMPurify allowlist is complete: Check that ALLOWED_TAGS and ALLOWED_ATTR in sanitizeHtml() include all legitimate tags/attributes needed for the drawer UI. Note: onmouseover and onmouseout are included - verify these are safe with DOMPurify's handling.
• Test the fallback behavior: If DOMPurify fails to load, sanitizeHtml() returns unsanitized HTML. Consider whether this is acceptable or if it should throw/return empty string instead.
• Manual XSS testing: Generate a flow visualization and attempt to inject XSS payloads (e.g., <script>alert(1)</script>, <img onerror=alert(1)>) through node names or metadata to verify they are properly sanitized.
• Verify visualization still works: Open a flow visualization and confirm the drawer content renders correctly with syntax highlighting, trigger conditions, and router paths.

Notes

• The Python tests verify code structure but cannot test actual browser runtime behavior
• DOMPurify is loaded from cdnjs CDN - offline usage will not have XSS protection

Closes #4326

Link to Devin run: https://app.devin.ai/sessions/9a0daac8e60c4f76a0f0e4371ec78644
Requested by: João

[devin-ai-integration]

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