419ecb3ce9
Coordinator ruling: a delivered chunk proves the Agent is alive (the analogue of OpcUaClient's good keep-alive), so TryMarkStreamDelivered - generation-checked under _subscriptionLock - also clears _writeDegraded. The degradation no longer sticks forever on a subscription-only driver. Test: unanswered write -> Degraded, stays Degraded with nothing else happening (positive control), the next chunk -> Healthy; red with the clear removed. Round-2 doc text corrected. Refs #743 Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT