fix(core): stop forcing toolChoice none on session.generate (#38557)

packages/core/src/session/generate-node.ts

@@ -74,7 +74,6 @@ export const layer = Layer.effect(
             system: contextEvent.system,
             messages: contextEvent.messages,
             tools: hookedTools,
-            toolChoice: "none",
           }),
         )
         yield* Effect.logInfo("session generation usage diagnostic", { usage: response.usage })

packages/core/test/session-generate.test.ts

@@ -301,7 +301,7 @@ it.effect("generates from fresh settled Session context without durable mutation
       ),
     ).toEqual(["Settled partial answer"])
     expect(requests[0]?.tools).toMatchObject([{ name: "lookup", description: "Hooked lookup" }])
-    expect(requests[0]?.toolChoice).toMatchObject({ type: "none" })
+    expect(requests[0]?.toolChoice).toBeUndefined()
     expect(yield* durableState(db, sessionID)).toEqual(before)
   }),
 )