fix(claude_sdk,conversations,rotation): context size from the last api call, new-day text by rotation reason

src/beaver_gateway/core/turn_capture.py

@@ -27,6 +27,12 @@ class TurnUsage:
     model_usage: dict[str, Any] | None = None
     """``ResultMessage.model_usage`` verbatim: per-model tokens, cost, web searches."""
 
+    context_tokens: int = 0
+    """Input of the last API call in the turn (fresh + cached + written to
+    cache) - the context size the model actually ran with, what Claude Code
+    shows as the context. The token fields above are sums over every API
+    call of the turn and grow with the number of tool calls."""
+
 
 @dataclass
 class TurnCapture: