Previously the endpoint silently returned 202 for all failures: missing agent identity, unregistered agents, empty payloads, and buffer-full drops. Now logs WARN for each failure case with context (instanceId, entry count, reason). Normal ingestion logged at INFO with accepted count. Buffer-full drops tracked individually with accepted/dropped counts. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>