Implement rate-limited Von agent email sending

[witbrock]

Outcome

Enables ordinary Von conversations to send authorised Gmail messages from the configured agent mailbox with an unavoidable AI-agent disclosure, durable delivery finality, canonical read-back, and administrator-controlled rate limits.

Key controls

• binds actor, organisation, namespace, request, and authorised Gmail profile from trusted server context
• requires the mailbox profile to represent the Von system identity and prevents ordinary relationship writes from self-granting mail authority
• injects visible and machine-readable AI-agent disclosure; rejects caller-supplied HTML in v1
• resolves a canonical mailbox identity before idempotency, quota, or provider dispatch
• records an absorbing delivery ledger and reconciles ambiguous responses through bounded Sent-mail fingerprint read-back
• exposes owner/admin settings for per-window, daily, per-message-recipient, and daily-recipient limits

Validation

• 145 impacted backend tests passed before the final reconciliation adjustment
• 102 relevant backend tests passed after the reconciliation adjustment
• final Gmail suite: 32 passed
• selected adaptive-turn suite: 12 passed
• settings UI Jest suite: 30 passed
• targeted Pyright: 0 errors
• focused Ruff, compilation, manifest parity, and git diff checks passed
• one authorised self-send was canonically read back; replay with the same request ID was a no-op

No model invocation was used for implementation or verification.