Harden local audit boundaries

[WalksWithASwagger]

Summary

• constrain knowledge-base writes to safe profile-local filenames
• spool audio uploads through temp files before transcription and avoid full service upload reads
• guard pickle cache/RAG loads against symlinks, outside-root paths, and shared-writable cache paths
• refresh status/roadmap closeout notes for the verified hardening lane

Verification

• git diff --check
• make docs-check
• make lint
• make test
• make pip-check
• make eval-fixture
• make smoke