feat(cli): implement output abstraction layer

packages/cli/src/output/json.ts

@@ -0,0 +1,34 @@
+/**
+ * JSON renderer for CLI output.
+ *
+ * Renders structured data as formatted JSON for machine consumption.
+ */
+
+import type { AnyCommandResult, OutputOptions } from './types.js'
+
+/** Render command result as JSON */
+export function renderJson<T>(
+  result: AnyCommandResult<T>,
+  _options: OutputOptions
+): string {
+  const { schema } = result
+
+  // Apply custom serializer if provided
+  if (schema.serialize) {
+    if (result.type === 'list') {
+      const serialized = result.data.map((item) => schema.serialize!(item))
+      return JSON.stringify(serialized, null, 2)
+    } else {
+      const serialized = schema.serialize(result.data)
+      return JSON.stringify(serialized, null, 2)
+    }
+  }
+
+  return JSON.stringify(result.data, null, 2)
+}
+
+/** Render a single item as JSON line (for NDJSON streaming) */
+export function renderJsonLine<T>(item: T, serialize?: (data: T) => unknown): string {
+  const output = serialize ? serialize(item) : item
+  return JSON.stringify(output)
+}