fix: route new prompt sync to target directory

Keeps optimistic prompt state in the session directory
Routes live assistant part updates using upstream event payloads
Adds regressions for startup session switch races

packages/ui/src/sync/session-actions.test.ts

@@ -159,6 +159,9 @@ import { INITIAL_STATE } from "./types"
 import type { DirectoryStore } from "./child-store"
 import type { Message, OpencodeClient, Part, Session } from "@opencode-ai/sdk/v2/client"
 
+type OptimisticAddCall = { sessionID: string; directory?: string | null; message: Message; parts: Part[] }
+type OptimisticRemoveCall = { sessionID: string; directory?: string | null; messageID: string }
+
 function createStore(
   permissions: Record<string, PermissionRequest[]>,
   state?: Partial<DirectoryStore>,
@@ -183,6 +186,56 @@ function createChildStores(entries: Array<[string, StoreApi<DirectoryStore>]>) {
   } as unknown as import("./child-store").ChildStoreManager
 }
 
+describe("optimisticSend target directory", () => {
+  beforeEach(() => {
+    replyCalls.length = 0
+    scopedClientDirectories.length = 0
+  })
+
+  test("passes the prompt directory to optimistic state during session switch races", async () => {
+    const currentStore = createStore({})
+    const targetStore = createStore({})
+    const childStores = createChildStores([
+      ["/current/project", currentStore],
+      ["/target/project", targetStore],
+    ])
+    let optimisticAdd: OptimisticAddCall | null = null
+    let optimisticRemove: OptimisticRemoveCall | null = null
+    let sentMessageID = ""
+
+    const { optimisticSend, setActionRefs, setOptimisticRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, childStores, () => "/current/project")
+    setOptimisticRefs(
+      (input) => {
+        optimisticAdd = input
+      },
+      (input) => {
+        optimisticRemove = input
+      },
+    )
+
+    await optimisticSend({
+      sessionId: "session-new",
+      directory: "/target/project",
+      content: "hello",
+      providerID: "provider",
+      modelID: "model",
+      send: async (messageID) => {
+        sentMessageID = messageID
+      },
+    })
+
+    expect(optimisticAdd).not.toBeNull()
+    const add = optimisticAdd as unknown as OptimisticAddCall
+    expect(add.directory).toBe("/target/project")
+    expect(add.sessionID).toBe("session-new")
+    expect(add.message.id).toBe(sentMessageID)
+    expect(optimisticRemove).toBe(null)
+    expect(targetStore.getState().session_status["session-new"]?.type).toBe("busy")
+    expect(currentStore.getState().session_status["session-new"]).toBe(undefined)
+  })
+})
+
 describe("respondToPermission passes directory", () => {
   beforeEach(() => {
     replyCalls.length = 0