🛡️ Sentinel: [HIGH] Add security headers & fix CORS

[google-labs-jules]

🛡️ Sentinel: [HIGH] Add security headers & fix CORS

🚨 Severity: HIGH
💡 Vulnerability:

1. Missing standard security headers (HSTS, CSP, X-Frame-Options) exposing users to clickjacking and MIME-sniffing.
2. Broken CORS configuration where Access-Control-Allow-Origin was not returned for allowed origins on non-preflight requests due to middleware ordering.

🎯 Impact:

1. Attackers could frame the API (if hosted publicly) or sniff content types.
2. Legitimate web clients from allowed origins would fail to access the API via POST/GET (browser blocks response).

🔧 Fix:

1. Added src/security-headers.ts middleware with strict CSP (default-src 'none'), HSTS, and other headers.
2. Modified src/http-transport.ts to apply security headers.
3. Fixed src/http-transport.ts to set CORS headers before early-exit checks, ensuring valid origins work.

✅ Verification:
npm test passes.
New tests in src/security-headers.test.ts and src/testing/http-integration.test.ts verify headers are present.

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PR created automatically by Jules for task 12447974312424747695 started by @davidruzicka

[google-labs-jules]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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