🛡️ Sentinel: [HIGH] Fix SQL injection in PRAGMA journal_mode statement

[mapleleaflatte03]

🚨 Severity: HIGH

💡 Vulnerability: The SQLite PRAGMA journal_mode statement is dynamically constructed using the MERIDIAN_OBSERVABILITY_SQLITE_JOURNAL_MODE environment variable. Because PRAGMA statements do not support standard SQL parameterization, directly concatenating user-controlled or external input into these statements can lead to SQL injection.

🎯 Impact: While environment variables are typically controlled by operators, any scenario where an attacker might influence this variable could allow them to execute arbitrary SQLite commands (e.g., dropping tables, modifying database structure, or exfiltrating data) through a chained injection.

🔧 Fix: Introduced a strict allowlist of valid SQLite journal modes (DELETE, TRUNCATE, PERSIST, MEMORY, WAL, OFF, ``, DEFAULT). If the configured mode is not in the allowlist, it securely defaults to `WAL`.

✅ Verification:

• Executed test_injection.py to confirm that appending malicious SQL commands to the environment variable no longer executes successfully.
• Unit tests (PYTHONPATH=intelligence/company/meridian_platform python3 -m unittest discover -s intelligence/company/meridian_platform -p "test_*.py") confirm normal database connectivity functions seamlessly without regression.

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PR created automatically by Jules for task 16881048076431060591 started by @mapleleaflatte03

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