fix(explain): preserve backend error details

apps/desktop/src/lib/backend/__tests__/getExplainInfo.spec.ts

@@ -0,0 +1,41 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  invoke: vi.fn(),
+}));
+
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: mocks.invoke,
+}));
+
+vi.mock("@tauri-apps/api/event", () => ({
+  listen: vi.fn(),
+}));
+
+describe("getExplainInfo backend error propagation", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it("preserves Tauri command errors", async () => {
+    const error = new Error("ORA-01031: insufficient privileges");
+    mocks.invoke.mockRejectedValue(error);
+    const { getExplainInfo } = await import("@/lib/backend/tauri");
+
+    await expect(getExplainInfo("oracle-1", "ORCL", "APP", "SELECT * FROM DUAL", "explain")).rejects.toBe(error);
+  });
+
+  it("preserves HTTP response errors", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockResolvedValue({
+        ok: false,
+        text: vi.fn().mockResolvedValue("Agent error: PLAN_TABLE is not accessible"),
+      }),
+    );
+    const { getExplainInfo } = await import("@/lib/backend/http");
+
+    await expect(getExplainInfo("oracle-1", "ORCL", "APP", "SELECT * FROM DUAL", "explain")).rejects.toThrow("Agent error: PLAN_TABLE is not accessible");
+  });
+});

apps/desktop/src/lib/backend/http.ts

@@ -810,12 +810,8 @@ export async function buildCreateUserSql(username: string, password: string, tab
 }
 
 export async function getExplainInfo(connectionId: string, database: string | undefined, schema: string | undefined, sql: string, mode: string): Promise<string | undefined> {
-  try {
-    const result = await post<string>("/api/query/get-explain-info", { connectionId, database, schema, sql, mode });
-    return result;
-  } catch {
-    return undefined;
-  }
+  // Match the Tauri path: transport and Agent failures must remain distinguishable from an empty plan.
+  return post<string>("/api/query/get-explain-info", { connectionId, database, schema, sql, mode });
 }
 
 export async function buildDroppedFilePreviewSql(options: DroppedFilePreviewSqlOptions): Promise<string | undefined> {

apps/desktop/src/lib/backend/tauri.ts

@@ -901,13 +901,8 @@ export async function buildCreateUserSql(username: string, password: string, tab
 }
 
 export async function getExplainInfo(connectionId: string, database: string | undefined, schema: string | undefined, sql: string, mode: string): Promise<string | undefined> {
-  try {
-    const result = await invoke<string>("get_explain_info", { connectionId, database, schema, sql, mode });
-    return result;
-  } catch (e: any) {
-    console.error("[getExplainInfo] invoke failed:", e?.message || e);
-    return undefined;
-  }
+  // Preserve Agent/driver errors so the explain view can show the actionable cause.
+  return invoke<string>("get_explain_info", { connectionId, database, schema, sql, mode });
 }
 
 export async function buildDroppedFilePreviewSql(options: DroppedFilePreviewSqlOptions): Promise<string | undefined> {