fix(errors): unify backend error protocol and preserve db detail

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

@@ -39,4 +39,24 @@ describe("appendQueryResultSegment spatial merge", () => {
     // Every row keeps its own SRID; a later page does not overwrite earlier cells.
     expect(merged.spatial_values).toEqual([[4326], [3857], [3857], [4490]]);
   });
+
+  it("raises the structured segment error instead of reconstructing from the Error row", () => {
+    const previous = make(1);
+    const segment = {
+      ...make(0),
+      execution_error: true as const,
+      rows: [["legacy row text"]],
+      error: {
+        version: 1 as const,
+        code: "DBX-JDBC-4001",
+        messageKey: "backendErrors.jdbc.sqlFailed",
+        messageParams: { stage: "execute" },
+        source: "jdbcAgent" as const,
+        operationOutcome: "unknown" as const,
+        detail: "relation missing_table does not exist",
+      },
+    } as unknown as QueryResult;
+
+    expect(() => appendQueryResultSegment(previous, segment, 100)).toThrow("relation missing_table does not exist");
+  });
 });

apps/desktop/src/stores/queryStore.ts

@@ -63,7 +63,7 @@ import { useSavedSqlStore } from "@/stores/savedSqlStore";
 import { useExportTracker } from "@/composables/useExportTracker";
 import { recordQueryCancellationLatency, resourceLifecycleDiagnostics } from "@/lib/diagnostics/resourceLifecycleDiagnostics";
 import { appendDebugLog } from "@/lib/backend/debugLog";
-import { formatError, normalizeBackendError, type BackendError } from "@/lib/backend/errorUtils";
+import { BackendErrorException, formatError, normalizeBackendError, type BackendError } from "@/lib/backend/errorUtils";
 import { createSavedSqlEditorPosition, initSavedSqlEditorPositions, restoreSavedSqlEditorPosition, saveSavedSqlEditorPosition } from "@/lib/app/savedSqlEditorPosition";
 import { ensureSqlExtension } from "@/lib/savedSql/savedSqlFileName";
 import { resolveSavedSqlExecutionTarget, savedSqlExecutionTargetFromTab, type SavedSqlExecutionTarget, type SavedSqlOpenTargetMode } from "@/lib/savedSql/savedSqlExecutionTarget";
@@ -161,7 +161,9 @@ function exactTotalFromIncompletePage(result: QueryResult, pageLimit: number | u
 }
 
 export function appendQueryResultSegment(previous: QueryResult, segment: QueryResult, maxRows: number): QueryResult {
-  if (segment.execution_error) throw new Error(String(segment.rows[0]?.[0] ?? "Failed to load the next result segment"));
+  if (segment.execution_error) {
+    throw segment.error ? new BackendErrorException(segment.error) : new BackendErrorException(String(segment.rows[0]?.[0] ?? "Failed to load the next result segment"));
+  }
   if (previous.columns.length !== segment.columns.length || previous.columns.some((column, index) => column !== segment.columns[index])) {
     throw new Error("Result columns changed while loading the next segment");
   }