feat(llm): add response reducer (#34417)

packages/llm/test/response.test.ts

@@ -0,0 +1,60 @@
+import { describe, expect, test } from "bun:test"
+import { LLMEvent, LLMResponse } from "../src"
+
+const reduce = (events: ReadonlyArray<LLMEvent>) => events.reduce(LLMResponse.reduce, LLMResponse.empty())
+
+describe("LLMResponse reducer", () => {
+  test("assembles interleaved reasoning and text with end metadata", () => {
+    const response = LLMResponse.fromEvents([
+      LLMEvent.reasoningStart({ id: "r1" }),
+      LLMEvent.reasoningDelta({ id: "r1", text: "I should " }),
+      LLMEvent.textStart({ id: "t1" }),
+      LLMEvent.reasoningDelta({ id: "r1", text: "compare..." }),
+      LLMEvent.reasoningEnd({ id: "r1", providerMetadata: { anthropic: { signature: "sig" } } }),
+      LLMEvent.textDelta({ id: "t1", text: "Answer" }),
+      LLMEvent.textEnd({ id: "t1" }),
+      LLMEvent.finish({ reason: "stop", usage: { outputTokens: 5 } }),
+    ])
+
+    expect(response?.finishReason).toBe("stop")
+    expect(response?.usage).toMatchObject({ outputTokens: 5 })
+    expect(response?.message.content).toEqual([
+      {
+        type: "reasoning",
+        text: "I should compare...",
+        providerMetadata: { anthropic: { signature: "sig" } },
+      },
+      { type: "text", text: "Answer" },
+    ])
+    expect(response?.events).toHaveLength(8)
+  })
+
+  test("preserves partial content without completing a failed stream", () => {
+    const state = reduce([LLMEvent.textStart({ id: "t1" }), LLMEvent.textDelta({ id: "t1", text: "partial" })])
+
+    expect(LLMResponse.complete(state)).toBeUndefined()
+    expect(state.message.content).toEqual([{ type: "text", text: "partial" }])
+  })
+
+  test("assembles tool-call content only after the completed tool call event", () => {
+    const pending = reduce([
+      LLMEvent.toolInputStart({ id: "call_1", name: "lookup" }),
+      LLMEvent.toolInputDelta({ id: "call_1", name: "lookup", text: '{"query"' }),
+    ])
+
+    expect(pending.message.content).toEqual([])
+    expect(pending.toolInputs.call_1?.text).toBe('{"query"')
+
+    const response = LLMResponse.fromEvents([
+      ...pending.events,
+      LLMEvent.toolInputDelta({ id: "call_1", name: "lookup", text: ':"weather"}' }),
+      LLMEvent.toolInputEnd({ id: "call_1", name: "lookup" }),
+      LLMEvent.toolCall({ id: "call_1", name: "lookup", input: { query: "weather" } }),
+      LLMEvent.finish({ reason: "tool-calls" }),
+    ])
+
+    expect(response?.message.content).toEqual([
+      { type: "tool-call", id: "call_1", name: "lookup", input: { query: "weather" } },
+    ])
+  })
+})