Add prepare rerun guidance for unresolved previous-session analyze inputs

internal/stage/analyze.go

@@ -631,6 +631,15 @@ func resolveScriptoriumInput(
 	runtimeCatalog *artifacts.ArtifactCatalog,
 ) (string, bool, *artifacts.ResolvedSessionArtifact, error) {
 	source := strings.TrimSpace(inputCfg.Source)
+	if artifacts.IsPreviousSessionArtifactSource(source) {
+		if inputCfg.Required {
+			return "", false, nil, fmt.Errorf(
+				"required previous-session input source %q is unavailable; run narratio run-stage --force prepare",
+				source,
+			)
+		}
+		return "", false, nil, nil
+	}
 	switch source {
 	case "previous_session_artifact":
 		if strings.TrimSpace(inputCfg.Path) == "" {

internal/stage/analyze_test.go

@@ -717,6 +717,25 @@ func TestAnalyzeOmitsOptionalMissingConfiguredArtifactInput(t *testing.T) {
 	}
 }
 
+func TestAnalyzeRequiredPreviousSessionArtifactInputGuidesPrepareForce(t *testing.T) {
+	env, m, _ := setupAnalyzeEnv(t)
+
+	sessionRecap := env.Config.Pipeline.Scriptorium.Artifacts["session_recap"]
+	sessionRecap.Inputs["previous_recap"] = config.ScriptoriumInputConfig{
+		Source:   "narratio.previous_session.artifact.session_recap",
+		Required: true,
+	}
+	env.Config.Pipeline.Scriptorium.Artifacts["session_recap"] = sessionRecap
+
+	_, err := (analyzeStage{}).Run(context.Background(), env, m)
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "run narratio run-stage --force prepare") {
+		t.Fatalf("error = %q, want guidance to run force prepare", err.Error())
+	}
+}
+
 func TestAnalyzeFailsWhenOutputPathMissing(t *testing.T) {
 	env, m, fake := setupAnalyzeEnv(t)
 	paths := sessionPathsForEnv(env, m.SessionID)