## ADDED Requirements

### Requirement: Per-tag SMS credits
Each tag SHALL track `sms_allocated`, `sms_used`, and `sms_period_start`. An allocation of 0 SHALL mean unmetered (no credit limit).

#### Scenario: Allocated plan
- **WHEN** an admin sets `sms_allocated = 10` on a tag
- **THEN** the tag may send up to 10 SMS in the period

#### Scenario: Unmetered default
- **WHEN** a tag has `sms_allocated = 0`
- **THEN** credit checks do not apply (transitional behaviour)

### Requirement: Credits required to send
Before sending an alert or finder-contact SMS on a metered tag, `sms_used < sms_allocated` SHALL hold. Each successful send SHALL increment `sms_used`. When exhausted, scans are recorded but no SMS is sent.

#### Scenario: Send consumes a credit
- **WHEN** an alert SMS is sent on a metered tag
- **THEN** `sms_used` increments by one

#### Scenario: Credits exhausted
- **WHEN** `sms_used >= sms_allocated` on a metered tag
- **THEN** further scans record but no SMS is sent
