feat(core): add embedded v2 session runtime and tool foundation (#30632)

packages/llm/test/provider/openai-chat.test.ts

@@ -50,6 +50,35 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("lowers chronological system updates to escaped user wrappers in order", () =>
+    Effect.gen(function* () {
+      const prepared = yield* LLMClient.prepare<OpenAIChat.OpenAIChatBody>(
+        LLM.request({
+          model,
+          messages: [Message.user("Before."), Message.system("Treat <admin> & data literally."), Message.assistant("After.")],
+        }),
+      )
+
+      expect(prepared.body.messages).toEqual([
+        { role: "user", content: "Before.\n<system-update>\nTreat &lt;admin&gt; &amp; data literally.\n</system-update>" },
+        { role: "assistant", content: "After." },
+      ])
+    }),
+  )
+
+  it.effect("replays canonical reasoning as OpenAI-compatible reasoning_content", () =>
+    Effect.gen(function* () {
+      const prepared = yield* LLMClient.prepare<OpenAIChat.OpenAIChatBody>(
+        LLM.request({
+          model,
+          messages: [Message.assistant([{ type: "reasoning", text: "thinking" }, { type: "text", text: "Hello" }])],
+        }),
+      )
+
+      expect(prepared.body.messages).toEqual([{ role: "assistant", content: "Hello", reasoning_content: "thinking" }])
+    }),
+  )
+
   it.effect("maps OpenAI provider options to Chat options", () =>
     Effect.gen(function* () {
       const prepared = yield* LLMClient.prepare<OpenAIChat.OpenAIChatBody>(
@@ -196,17 +225,17 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
-  it.effect("rejects unsupported assistant reasoning content", () =>
+  it.effect("lowers reasoning-only assistant history", () =>
     Effect.gen(function* () {
-      const error = yield* LLMClient.prepare(
+      const prepared = yield* LLMClient.prepare<OpenAIChat.OpenAIChatBody>(
         LLM.request({
           id: "req_reasoning",
           model,
           messages: [Message.assistant({ type: "reasoning", text: "hidden" })],
         }),
-      ).pipe(Effect.flip)
+      )
 
-      expect(error.message).toContain("OpenAI Chat assistant messages only support text and tool-call content for now")
+      expect(prepared.body.messages).toEqual([{ role: "assistant", content: null, reasoning_content: "hidden" }])
     }),
   )