Add execution control request contracts

internal/domain/domain.go

@@ -1,6 +1,7 @@
 package domain
 
 import (
+	"context"
 	"time"
 )
 
@@ -60,6 +61,9 @@ type CacheControl struct {
 
 // RunRequest represents a request to generate a single artifact.
 type RunRequest struct {
+	OperationTimeout time.Duration
+	// OnPrepared receives borrowed, read-only internal state.
+	OnPrepared       func(context.Context, *PreparedRun)
 	CaptureExchange  bool
 	ContinueFrom     *Exchange
 	PromptID         string