🛡️ Sentinel: [security improvement] harden CSP and button handling

[Shin5hi]

🛡️ Sentinel Security Enhancement Report

Severity: LOW (Security Enhancement / Defense in Depth)

💡 Vulnerability/Improvement:

1. Loose CSP: The existing Content Security Policy lacked a form-action directive, which could potentially allow form submissions to unauthorized endpoints if an injection occurred.
2. Defensive Programming Gap: Dynamically created buttons lacked an explicit type="button", which defaults to "submit" inside forms, potentially causing unintended side effects.
3. Legacy Event Handling: Use of .onclick is less robust than addEventListener.

🎯 Impact:

• Improved protection against CSRF and unauthorized data exfiltration via form injections.
• Enhanced application stability and consistency by ensuring buttons behave predictably.

🔧 Fix:

• Updated index.html meta tag to include form-action 'none'.
• Modified inline JavaScript to explicitly set closeBtn.type = 'button'.
• Refactored closeBtn.onclick to closeBtn.addEventListener('click', ...).
• Recalculated and updated the SHA-256 hash for the inline script in the CSP header.

✅ Verification:

• Verified using Playwright that the application remains functional.
• Confirmed no CSP violations occur in the browser console during the primary user journey (triggering and dismissing notifications).
• Visually verified the success state via screenshots and video.

Critical Learning:
Recorded in .jules/sentinel.md regarding Playwright's wait_for_function triggering unsafe-eval CSP violations, necessitating a switch to expect or native handles for verification in hardened environments.

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PR created automatically by Jules for task 4979087973990462723 started by @Shin5hi

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