From 9715b6c23cafdc1ae005d953d918f48f16e11ed3 Mon Sep 17 00:00:00 2001
From: Isaac Sanchez-Hawkins <266845420+isanchez404@users.noreply.github.com>
Date: Fri, 8 May 2026 16:14:07 -0400
Subject: [PATCH] fix(sync): preserve part update ordering (#1167)

* fix(sync): preserve part update ordering

* test(sync): wait for pipeline delivery

---------

Co-authored-by: Isaac Sanchez <isanchez-hawkins@arize.com>
---
 packages/ui/src/sync/event-pipeline.test.ts | 99 +++++++++++++++++++++
 packages/ui/src/sync/event-pipeline.ts      |  4 -
 2 files changed, 99 insertions(+), 4 deletions(-)
 create mode 100644 packages/ui/src/sync/event-pipeline.test.ts

diff --git a/packages/ui/src/sync/event-pipeline.test.ts b/packages/ui/src/sync/event-pipeline.test.ts
new file mode 100644
index 00000000..9a4ea81f
--- /dev/null
+++ b/packages/ui/src/sync/event-pipeline.test.ts
@@ -0,0 +1,99 @@
+import { describe, expect, test } from "bun:test"
+import type { Event, OpencodeClient } from "@opencode-ai/sdk/v2/client"
+import { createEventPipeline } from "./event-pipeline"
+
+const failAfter = (ms: number) => new Promise<never>((_, reject) => {
+  setTimeout(() => reject(new Error("Timed out waiting for event pipeline flush")), ms)
+})
+
+function partUpdatedEvent(text: string): Event {
+  return {
+    type: "message.part.updated",
+    properties: {
+      part: {
+        id: "prt_1",
+        messageID: "msg_1",
+        sessionID: "ses_1",
+        type: "text",
+        text,
+      },
+    },
+  } as Event
+}
+
+function deltaEvent(delta: string): Event {
+  return {
+    type: "message.part.delta",
+    properties: {
+      messageID: "msg_1",
+      partID: "prt_1",
+      field: "text",
+      delta,
+    },
+  } as Event
+}
+
+function createSdk(events: Event[], streamFinished: () => void): OpencodeClient {
+  return {
+    global: {
+      event: async ({ signal }: { signal: AbortSignal }) => ({
+        stream: (async function* () {
+          for (const payload of events) {
+            yield { directory: "/repo", payload }
+          }
+          streamFinished()
+          await new Promise<void>((resolve) => {
+            if (signal.aborted) {
+              resolve()
+              return
+            }
+            signal.addEventListener("abort", () => resolve(), { once: true })
+          })
+        })(),
+      }),
+    },
+  } as unknown as OpencodeClient
+}
+
+describe("createEventPipeline", () => {
+  test("preserves part update order around text deltas", async () => {
+    let resolveStreamFinished!: () => void
+    const streamFinished = new Promise<void>((resolve) => {
+      resolveStreamFinished = resolve
+    })
+    let resolveDelivered!: () => void
+    const deliveredAll = new Promise<void>((resolve) => {
+      resolveDelivered = resolve
+    })
+    const delivered: Event[] = []
+    const pipeline = createEventPipeline({
+      sdk: createSdk([
+        partUpdatedEvent("a"),
+        deltaEvent("b"),
+        partUpdatedEvent("ab"),
+      ], resolveStreamFinished),
+      onEvent: (_directory, payload) => {
+        delivered.push(payload)
+        if (delivered.length === 3) {
+          resolveDelivered()
+        }
+      },
+      transport: "sse",
+      heartbeatTimeoutMs: 1_000,
+    })
+
+    try {
+      await streamFinished
+      await Promise.race([deliveredAll, failAfter(500)])
+    } finally {
+      pipeline.cleanup()
+    }
+
+    expect(delivered.map((event) => {
+      if (event.type === "message.part.delta") {
+        return `delta:${(event.properties as { delta: string }).delta}`
+      }
+      return `updated:${((event.properties as { part: { text: string } }).part).text}`
+    })).toEqual(["updated:a", "delta:b", "updated:ab"])
+  })
+})
diff --git a/packages/ui/src/sync/event-pipeline.ts b/packages/ui/src/sync/event-pipeline.ts
index e680c536..7e8282a8 100644
--- a/packages/ui/src/sync/event-pipeline.ts
+++ b/packages/ui/src/sync/event-pipeline.ts
@@ -211,10 +211,6 @@ export function createEventPipeline(input: EventPipelineInput) {
     if (payload.type === "lsp.updated") {
       return "lsp.updated"
     }
-    if (payload.type === "message.part.updated") {
-      const part = (payload.properties as { part: { messageID: string; id: string } }).part
-      return `message.part.updated:${part.messageID}:${part.id}`
-    }
     if (payload.type === "message.part.delta") {
       const props = payload.properties as { messageID: string; partID: string; field: string }
       return `message.part.delta:${props.messageID}:${props.partID}:${props.field}`