fix(opencode): clone part data in Bus event to preserve token values (#15780)

packages/opencode/src/session/index.ts

@@ -761,7 +761,7 @@ export namespace Session {
         .run()
       Database.effect(() =>
         Bus.publish(MessageV2.Event.PartUpdated, {
-          part,
+          part: structuredClone(part),
         }),
       )
     })

packages/opencode/test/session/session.test.ts

@@ -4,6 +4,8 @@ import { Session } from "../../src/session"
 import { Bus } from "../../src/bus"
 import { Log } from "../../src/util/log"
 import { Instance } from "../../src/project/instance"
+import { MessageV2 } from "../../src/session/message-v2"
+import { Identifier } from "../../src/id/id"
 
 const projectRoot = path.join(__dirname, "../..")
 Log.init({ print: false })
@@ -69,3 +71,68 @@ describe("session.started event", () => {
     })
   })
 })
+
+describe("step-finish token propagation via Bus event", () => {
+  test("non-zero tokens propagate through PartUpdated event", async () => {
+    await Instance.provide({
+      directory: projectRoot,
+      fn: async () => {
+        const session = await Session.create({})
+
+        const messageID = Identifier.ascending("message")
+        await Session.updateMessage({
+          id: messageID,
+          sessionID: session.id,
+          role: "user",
+          time: { created: Date.now() },
+          agent: "user",
+          model: { providerID: "test", modelID: "test" },
+          tools: {},
+          mode: "",
+        } as unknown as MessageV2.Info)
+
+        let received: MessageV2.Part | undefined
+        const unsub = Bus.subscribe(MessageV2.Event.PartUpdated, (event) => {
+          received = event.properties.part
+        })
+
+        const tokens = {
+          total: 1500,
+          input: 500,
+          output: 800,
+          reasoning: 200,
+          cache: { read: 100, write: 50 },
+        }
+
+        const partInput = {
+          id: Identifier.ascending("part"),
+          messageID,
+          sessionID: session.id,
+          type: "step-finish" as const,
+          reason: "stop",
+          cost: 0.005,
+          tokens,
+        }
+
+        await Session.updatePart(partInput)
+
+        await new Promise((resolve) => setTimeout(resolve, 100))
+
+        expect(received).toBeDefined()
+        expect(received!.type).toBe("step-finish")
+        const finish = received as MessageV2.StepFinishPart
+        expect(finish.tokens.input).toBe(500)
+        expect(finish.tokens.output).toBe(800)
+        expect(finish.tokens.reasoning).toBe(200)
+        expect(finish.tokens.total).toBe(1500)
+        expect(finish.tokens.cache.read).toBe(100)
+        expect(finish.tokens.cache.write).toBe(50)
+        expect(finish.cost).toBe(0.005)
+        expect(received).not.toBe(partInput)
+
+        unsub()
+        await Session.remove(session.id)
+      },
+    })
+  }, { timeout: 30000 })
+})