Observe claimed prepared executions

types.go

@@ -143,8 +143,11 @@ type RunRequest struct {
 	// Negative values are invalid for Prepare, PrepareExecution, and Run.
 	// Injected LLMClient implementations remain single-dispatch.
 	TransientRetries *int
-	// Observer receives metadata about this Run invocation synchronously. It is
+	// Observer receives metadata about an execution invocation synchronously. It is
 	// excluded from JSON and is not invoked by Prepare or PrepareExecution.
+	// Successful PrepareExecution retains the function for its RunPrepared call;
+	// Discard or a completed claim clears that reference. The closure itself is
+	// not copied, so callers must synchronize its shared state.
 	Observer ExecutionObserver `json:"-"`
 }