v0.4.0 — Security & Performance Hardening

Breaking Changes

• HMAC key now required — FailSafeAuditSink(hmac_key=...) no longer defaults to a dev key. Pass hmac_key=b"failsafe-dev-key" explicitly for development or set a production key.

Security Hardening

• DecisionRequest.__post_init__ validates action, agent_did, and normalizes artifact_path via os.path.normpath
• Exception messages sanitized — no str(exc) leak in fail-open responses
• Artifact paths in webhook events reduced to os.path.basename only
• SLI signal reasons truncated to 200 chars max
• Escalation queue eviction now runs under lock

Performance

• Persistent SQLite connections with WAL mode and busy_timeout=5000 in both LocalFailSafeClient and FailSafeAuditSink
• LocalFailSafeClient.close() method for explicit connection cleanup
• MCP client subprocess cleanup on handshake failure

Reliability

• fail_open: bool = True parameter on FailSafeInterceptor and GovernancePipeline
• Fail-closed mode raises on governance errors instead of silently allowing
• Trust score diminishing returns: 0.8 ** consecutive_successes decay prevents score inflation

Stats

• 18 source files, 3,387 lines
• 305 tests passing, clean lint

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com