Replaces the pass-through skeleton with a lazily rolled fixed window:
admit() charges one message against the current epoch, resets the
counter once epochPeriodSec has elapsed, and rejects with OverBudget
when messagesPerEpoch is exhausted. Disabled or non-positive
configurations admit everything, so the default-constructed
MessagingClientConf (enabled = false) keeps today's behaviour.
Parking of over-budget messages stays with the SendService scheduler
(NextRoundRetry); the manager only answers whether one more
transmission fits. The queue / dequeueReady stubs that anticipated
manager-side parking are removed accordingly.
Extends tests/messaging/test_rate_limit_manager.nim with budget
boundary, epoch rollover, resetEpoch, and degenerate-config cases,
replacing the enabled-pass-through placeholder test.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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