Threats and mitigations

Device theft/loss             — OS keychain/keystore, encryption at rest,
                                biometric lock
Network interception          — TLS, certificate pinning
Prompt-injection exfiltration — the outbound guard limits what can ever be
                                sent; sanitize retrieved content
Model provider leakage        — BAA, zero-retention settings, send
                                minimum-necessary
Re-identification via leaked variants — don't transmit the sequence

Logging itself is a threat surface — never log PHI; log ids and metadata only.