The Rhai SDK email::send path went straight to the SMTP relay with no
admission control. EmailRateLimiter lived in users_service.rs (gating
verification + password-reset emails) but was unreachable from the SDK
surface. Any anonymous-callable HTTP-route script could loop email::send
to burn the operator's SMTP quota or BCC-bomb thousands of recipients
per request.
Two new caps on EmailServiceImpl, both fire BEFORE message assembly +
SMTP connect:
1. Per-message recipient cap (to+cc+bcc combined). Default 20, override
with PICLOUD_EMAIL_MAX_RECIPIENTS. New EmailError::TooManyRecipients
variant. Closes the BCC-bomb amplification path.
2. EmailRateLimiter inlined into EmailServiceImpl:
* Per-(app, recipient): RECIPIENT_BURST=5 / RECIPIENT_WINDOW=60min.
* Per-app daily: APP_DAILY_CAP=200 / 24h.
The structure mirrors users_service's private limiter; defense-in-
depth redundancy is fine since the gates are identical and never
conflict. New EmailError::RateLimited(&'static str) variant; the
string names which bucket tripped so the operator can act.
users_service::map_email_error grows two cases (mapped to
EmailTransport for the script-facing error shape).
Tests:
* too_many_recipients_rejected — 30 recipients, default cap 20, rejected
with TooManyRecipients.
* per_recipient_burst_caps_repeated_send_to_same_address — 6 sends to
the same address; 6th returns RateLimited("per-recipient burst").
Audit ref: security_audit/09_external_integrations.md#f-ext-h-001.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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