Add native LLM core foundation (#24712)

packages/llm/test/lib/openai-chunks.ts

@@ -0,0 +1,27 @@
+/**
+ * Shared chunk shapes for OpenAI Chat / OpenAI-compatible Chat fixture tests.
+ * Multiple test files build the same `{ id, choices: [{ delta, finish_reason }], usage }`
+ * envelope; consolidating here keeps tool-call event shapes consistent.
+ */
+
+const FIXTURE_ID = "chatcmpl_fixture"
+
+export const deltaChunk = (delta: object, finishReason: string | null = null) => ({
+  id: FIXTURE_ID,
+  choices: [{ delta, finish_reason: finishReason }],
+  usage: null,
+})
+
+export const usageChunk = (usage: object) => ({
+  id: FIXTURE_ID,
+  choices: [],
+  usage,
+})
+
+export const finishChunk = (reason: string) => deltaChunk({}, reason)
+
+export const toolCallChunk = (id: string, name: string, args: string, index = 0) =>
+  deltaChunk({
+    role: "assistant",
+    tool_calls: [{ index, id, function: { name, arguments: args } }],
+  })