🛡️ Sentinel: [CRITICAL] Fix SQL injection in SQLite PRAGMA statement

[mapleleaflatte03]

🚨 Severity: CRITICAL

💡 Vulnerability: In intelligence/company/meridian_platform/observability_store.py, the MERIDIAN_OBSERVABILITY_SQLITE_JOURNAL_MODE environment variable was used directly in an f-string to construct a PRAGMA journal_mode= SQL statement.

🎯 Impact: Because SQLite PRAGMA statements do not support parameterized queries (?), interpolating unvalidated inputs creates a SQL injection vulnerability. Although sqlite3.Connection.execute() prevents multiple semicolon-separated statements (which limits the blast radius), an attacker who can control environment variables could potentially exploit this injection vector.

🔧 Fix: Implemented a strict allowlist validation check. The configured_journal_mode is now explicitly checked against all safe, valid SQLite journal modes (DELETE, TRUNCATE, PERSIST, MEMORY, WAL, OFF) as well as internal bypass values (DEFAULT, ''). Any unrecognized value is safely overridden with the default WAL.

✅ Verification:

1. Run PYTHONPATH=intelligence/company/meridian_platform:intelligence:kernel python3 -m unittest intelligence/company/meridian_platform/test_status_surface.py intelligence/company/meridian_platform/test_alerting.py
2. Tests pass (any offset-naive datetime exceptions are existing environment artifacts).
3. The journal logging setup handles invalid environment values cleanly without executing them as SQL.

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PR created automatically by Jules for task 3335065020537012677 started by @mapleleaflatte03

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