Prepare requests with captured conversation history

internal/domain/domain.go

@@ -60,6 +60,8 @@ type CacheControl struct {
 
 // RunRequest represents a request to generate a single artifact.
 type RunRequest struct {
+	CaptureExchange  bool
+	ContinueFrom     *Exchange
 	PromptID         string
 	ProfileID        string
 	SessionID        string
@@ -98,6 +100,7 @@ type RunResult struct {
 // PreparedRun contains pre-LLM execution state from the prepare/render phase.
 // It must never include resolved API key values, model output, or validation data.
 type PreparedRun struct {
+	ParentRunID          string
 	PromptID             string
 	PromptHash           string
 	SelectedProfileID    string