fix(transfer): support default tree-schema databases

Closes #7104

apps/desktop/src/lib/__tests__/database/dataTransferSelection.spec.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
-import { isSameTransferDatabase, normalizeTransferCatalog, type TransferDatabaseSelection } from "@/lib/database/dataTransferSelection";
+import { decodeTransferDatabaseOption, encodeTransferDatabaseOptions, isSameTransferDatabase, isTransferDatabaseSelected, normalizeTransferCatalog, type TransferDatabaseSelection } from "@/lib/database/dataTransferSelection";
+import { TREE_SCHEMA_DEFAULT_DATABASE_SELECT_VALUE } from "@/lib/database/defaultDatabase";
 import type { CatalogInfo } from "@/types/database";
 
 function catalog(name: string, catalog_type: string): CatalogInfo {
@@ -17,6 +18,27 @@ function selection(overrides: Partial<TransferDatabaseSelection> = {}): Transfer
 }
 
 describe("data transfer database selection", () => {
+  it("keeps a Kingbase default database distinct from no selection", () => {
+    const options = encodeTransferDatabaseOptions("kingbase", [""]);
+
+    expect(options).toEqual([TREE_SCHEMA_DEFAULT_DATABASE_SELECT_VALUE]);
+    expect(isTransferDatabaseSelected(options[0])).toBe(true);
+    expect(isTransferDatabaseSelected("")).toBe(false);
+    expect(decodeTransferDatabaseOption("kingbase", options[0])).toBe("");
+  });
+
+  it("uses the tree-schema default database contract for PostgreSQL", () => {
+    const [option] = encodeTransferDatabaseOptions("postgres", [""]);
+
+    expect(option).toBe(TREE_SCHEMA_DEFAULT_DATABASE_SELECT_VALUE);
+    expect(decodeTransferDatabaseOption("postgres", option)).toBe("");
+  });
+
+  it.each(["kingbase", "dameng", "mysql", "mongodb", "starrocks"] as const)("preserves named %s databases", (databaseType) => {
+    expect(encodeTransferDatabaseOptions(databaseType, ["app", "analytics"])).toEqual(["app", "analytics"]);
+    expect(decodeTransferDatabaseOption(databaseType, "analytics")).toBe("analytics");
+  });
+
   it("normalizes empty, Doris internal, and StarRocks default catalogs", () => {
     expect(normalizeTransferCatalog("", [])).toBe("");
     expect(normalizeTransferCatalog("internal", [])).toBe("");