fix(sync): drop orphan session parts (#1183)

* fix(sync): drop orphan session parts

* fix(sync): guard missing part cache

---------

Co-authored-by: Isaac Sanchez <isanchez-hawkins@arize.com>

packages/ui/src/sync/__tests__/eviction.test.ts

@@ -1,11 +1,11 @@
 import { describe, expect, test } from "bun:test"
-import type { Message, PermissionRequest, QuestionRequest } from "@opencode-ai/sdk/v2/client"
+import type { Message, Part, PermissionRequest, QuestionRequest } from "@opencode-ai/sdk/v2/client"
 import {
   canDisposeDirectory,
   hasPendingBlockingRequests,
   pickDirectoriesToEvict,
 } from "../eviction"
-import { getProtectedSessionCacheIds, pickSessionCacheEvictions } from "../session-cache"
+import { dropSessionCaches, getProtectedSessionCacheIds, pickSessionCacheEvictions } from "../session-cache"
 import { INITIAL_STATE, type DirState, type State } from "../types"
 
 const DAY_MS = 24 * 60 * 60 * 1000
@@ -172,4 +172,20 @@ describe("session cache eviction", () => {
     expect(seen.has("ses_question")).toBe(true)
     expect(seen.has("ses_streaming")).toBe(true)
   })
+
+  test("drops parts for evicted messages without part session ids", () => {
+    const store = buildState({
+      message: {
+        ses_old: [{ id: "msg_1", role: "user", time: { created: 1 } } as Message],
+      },
+      part: {
+        msg_1: [{ id: "prt_1", messageID: "msg_1" } as Part],
+      },
+    })
+
+    dropSessionCaches(store, ["ses_old"])
+
+    expect(store.message.ses_old).toBe(undefined)
+    expect(store.part.msg_1).toBe(undefined)
+  })
 })