feat(cli): formalize dev-friendly result output

packages/cli/src/io/print-list.ts

@@ -28,6 +28,16 @@ export interface PrintListArgs<Row> {
   io: KtxCliIo;
 }
 
+export interface KtxJsonResultEnvelope<T> {
+  kind: string;
+  data: T;
+  meta?: Record<string, unknown>;
+}
+
+export function writeJsonResult<T>(io: KtxCliIo, envelope: KtxJsonResultEnvelope<T>): void {
+  io.stdout.write(`${JSON.stringify(envelope, null, 2)}\n`);
+}
+
 export function printList<Row extends object>(args: PrintListArgs<Row>): void {
   switch (args.mode) {
     case 'json':
@@ -61,12 +71,11 @@ function printListPlain<Row extends object>(args: PrintListArgs<Row>): void {
 }
 
 function printListJson<Row extends object>(args: PrintListArgs<Row>): void {
-  const envelope = {
+  writeJsonResult(args.io, {
     kind: 'list',
     data: { items: args.rows },
     meta: { command: args.command },
-  };
-  args.io.stdout.write(`${JSON.stringify(envelope, null, 2)}\n`);
+  });
 }
 
 function pluralize(count: number, singular: string): string {

packages/cli/src/sl.test.ts

@@ -398,10 +398,18 @@ joins: []
       listIo.io,
     );
     expect(code).toBe(0);
+    expect(listIo.stderr()).toBe('');
 
     const parsed = JSON.parse(listIo.stdout());
-    expect(parsed.kind).toBe('list');
-    expect(parsed.meta).toEqual({ command: 'sl list' });
+    expect(parsed).toMatchObject({
+      kind: 'list',
+      data: {
+        items: expect.any(Array),
+      },
+      meta: {
+        command: 'sl list',
+      },
+    });
     expect(parsed.data.items).toHaveLength(1);
     expect(parsed.data.items[0]).toMatchObject({
       connectionId: 'warehouse',