Add regression test for JSON schema load failure during prepare

internal/usecase/runner_test.go

@@ -490,6 +490,35 @@ func TestRunnerPrepareJSONSchemaBuildsStructuredOutputSpec(t *testing.T) {
 	}
 }
 
+func TestRunnerPrepareJSONSchemaSchemaLoadFailureReturnsValidationError(t *testing.T) {
+	def := promptDef(domain.FormatJSON, domain.ValidationJSONSchema, 0)
+	def.Validation.SchemaPath = "missing.schema.json"
+	validator := &fakeValidator{schemaErr: errors.New("schema unavailable")}
+	runner := NewRunner(
+		&fakePromptRepo{def: def},
+		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+		defaultArtifactReader(),
+		defaultRenderer(),
+		&fakeLLM{forbid: true},
+		validator,
+	)
+
+	_, err := runner.Prepare(context.Background(), domain.RunRequest{
+		PromptID:  "p",
+		ProfileID: "exec",
+		Inputs:    singleInputRef(),
+	})
+	if !errors.Is(err, ErrValidation) {
+		t.Fatalf("expected ErrValidation, got %v", err)
+	}
+	if validator.schemaLoads != 1 {
+		t.Fatalf("expected one schema load attempt, got %d", validator.schemaLoads)
+	}
+	if validator.schemaLoadPath != "missing.schema.json" {
+		t.Fatalf("expected schema path missing.schema.json, got %q", validator.schemaLoadPath)
+	}
+}
+
 func TestRunnerRunJSONSchemaSchemaLoadFailureFailsBeforeLLM(t *testing.T) {
 	def := promptDef(domain.FormatJSON, domain.ValidationJSONSchema, 0)
 	def.Validation.SchemaPath = "missing.schema.json"