fix: wire VectorDBInjectionDetector into proxy + runtime audit

[msaad00]

Summary

• VectorDBInjectionDetector was implemented and tested but never wired into the live proxy — it only existed as dead code at runtime
• runtime/__init__.py also didn't export it, so external callers couldn't use it
• AUDIT.md expanded with full runtime/API/data-flow audit (Areas 4–6)

Changes

src/agent_bom/runtime/__init__.py

• Added VectorDBInjectionDetector to imports and __all__

src/agent_bom/proxy.py

• Instantiates VectorDBInjectionDetector alongside ResponseInspector
• Calls vector_detector.check() on every tool response in relay_server_to_client()
• For confirmed vector tool names (similarity_search, retrieve, rag_query, fetch_context, etc.) severity is upgraded to CRITICAL and alerts are tagged cache_poison_*

AUDIT.md

• Added Area 4 (Runtime layer): proxy data flow, 7 detectors table, fixed issues
• Added Area 5 (API layer): FastAPI middleware stack, auth/audit log security properties
• Added Area 6 (Data flow): end-to-end pipeline diagram
• Updated audit summary table
• Updated next-audit checklist

Test plan

• tests/test_runtime_detectors.py — all 88 tests pass (VectorDBInjectionDetector already tested)
• tests/test_proxy.py — proxy relay tests pass
• tests/test_proxy_metrics.py — metrics tests pass

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None