fix(query): preserve original backend errors with fallback detail

apps/desktop/src/stores/__tests__/queryStore.multiStatementError.spec.ts

@@ -1,5 +1,6 @@
 import { createPinia, setActivePinia } from "pinia";
 import { isActiveResultLoading } from "@/lib/sql/queryExecutionState";
+import { BackendErrorException } from "@/lib/backend/errorUtils";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
 const mocks = vi.hoisted(() => ({
@@ -173,6 +174,42 @@ describe("queryStore multi-statement errors", () => {
     expect(tab.batchSqlExecution?.items[1]?.errorDetails).toEqual(structuredError);
     expect(tab.batchSqlExecution?.items[1]?.error).not.toBe(structuredError.code);
     expect(tab.batchSqlExecution?.items[1]?.error).not.toBe("[object Object]");
+    expect(tab.batchSqlExecution?.items[1]?.error).toContain("no such table: missing");
+  });
+
+  it("preserves the original message when a top-level structured error omits detail", async () => {
+    const structuredError = {
+      version: 1 as const,
+      code: "DBX-LEGACY-0001",
+      messageKey: "backendErrors.legacy",
+      messageParams: {},
+      source: "legacyBackend" as const,
+      operationOutcome: "unknown" as const,
+    };
+    const originalMessage = "ClickHouse error: table iceberg_backend.missing_table does not exist";
+    mocks.getConnectionConfig.mockReturnValue({
+      id: "clickhouse-1",
+      name: "ClickHouse",
+      db_type: "clickhouse",
+      database: "iceberg_backend",
+      query_timeout_secs: 30,
+    });
+    mocks.executeMulti.mockRejectedValue(
+      new BackendErrorException({
+        backendError: structuredError,
+        message: originalMessage,
+      }),
+    );
+    const { useQueryStore } = await import("@/stores/queryStore");
+    const store = useQueryStore();
+    const tabId = store.createTab("clickhouse-1", "iceberg_backend", "Query");
+
+    await store.executeTabSql(tabId, "SELECT * FROM missing_table");
+
+    const tab = store.tabs.find((item) => item.id === tabId)!;
+    expect(tab.result?.execution_error).toBe(true);
+    expect(tab.result?.rows[0]?.[0]).toContain(originalMessage);
+    expect(tab.batchSqlExecution?.items[0]?.error).toContain(originalMessage);
   });
 
   it("updates live per-statement progress before the batch promise resolves", async () => {

apps/desktop/src/stores/queryStore.ts

@@ -411,7 +411,7 @@ function reconcileBatchSqlResults(tab: QueryTab, executionId: string, results: Q
     item.executionTimeMs = result.execution_time_ms;
     item.affectedRows = result.affected_rows;
     item.errorDetails = failed ? result.error : undefined;
-    item.error = failed ? (result.error ? translateBackendError(i18n.global.t, result.error) : String(result.rows[0]?.[0] ?? "")) : undefined;
+    item.error = failed ? (result.error ? translateBackendError(i18n.global.t, result.error, result.rows[0]?.[0]) : String(result.rows[0]?.[0] ?? "")) : undefined;
   }
   batch.completed = batch.items.filter((item) => item.status === "success" || item.status === "error").length;
 }
@@ -423,7 +423,7 @@ function failBatchSqlExecution(tab: QueryTab, executionId: string, error: unknow
   if (!item) return;
   item.status = cancelled ? "cancelled" : "error";
   item.errorDetails = cancelled ? undefined : (normalizeBackendError(error) ?? undefined);
-  item.error = cancelled ? undefined : translateBackendError(i18n.global.t, error);
+  item.error = cancelled ? undefined : translateBackendError(i18n.global.t, error, error instanceof Error ? error.message : undefined);
   batch.completed = batch.items.filter((candidate) => candidate.status === "success" || candidate.status === "error").length;
 }
 
@@ -3856,7 +3856,7 @@ export const useQueryStore = defineStore("query", () => {
     // Single funnel for every query execution failure, so backend messages DBX
     // knows about are shown in the active locale rather than as raw English.
     const error = normalizeBackendError(e) ?? undefined;
-    const message = translateBackendError(i18n.global.t, e);
+    const message = translateBackendError(i18n.global.t, e, e instanceof Error ? e.message : undefined);
     return markQueryResultRowsRaw({
       columns: ["Error"],
       execution_error: true,