DeepSeek V4 requires reasoning_content on EVERY assistant turn once any
prior turn included it, not just tool-call turns. Previously the replay
logic only triggered for tool-call turns, which caused 400 errors on
plain-text assistant follow-ups in multi-turn conversations.
Key change: the replay conditions now use needsReasoningField (all turns
for strict providers) instead of toolCalls.length > 0.
Burke T
1c31ef015d