Track the operation owning internal errors

internal/usecase/operation_error_test.go

@@ -0,0 +1,34 @@
+package usecase
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"go.maximumdirect.net/promptkit/internal/profile"
+	"go.maximumdirect.net/promptkit/internal/promptdef"
+)
+
+func TestOperationErrorRetainsOwnerAndCause(t *testing.T) {
+	cause := fmt.Errorf("nested: %w", promptdef.ErrPromptDefinitionNotFound)
+	outer := &OperationError{Category: ErrLLMGenerate, Cause: cause}
+	if !errors.Is(outer, ErrLLMGenerate) || !errors.Is(outer, promptdef.ErrPromptDefinitionNotFound) || errors.Unwrap(outer) != cause {
+		t.Fatalf("operation error = %v", outer)
+	}
+	for _, test := range []struct {
+		err      error
+		category error
+	}{
+		{promptLookupError(cause), promptdef.ErrPromptDefinitionNotFound},
+		{profileLookupError(profile.ErrProfileNotFound), profile.ErrProfileNotFound},
+		{promptLookupError(contextFailure), ErrPromptLoad},
+		{profileLookupError(contextFailure), ErrProfileLoad},
+	} {
+		var operation *OperationError
+		if !errors.As(test.err, &operation) || operation.Category != test.category {
+			t.Errorf("operation = %+v", operation)
+		}
+	}
+}
+
+var contextFailure = errors.New("lookup failed")