From c3111fe15fd21fcf7c2235b04a457e2893ebb81f Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Sat, 8 Aug 2026 21:18:27 -0400
Subject: [PATCH] fix(tui): undo latest pending prompt

---
 packages/tui/src/routes/session/index.tsx | 20 ++++++----
 packages/tui/src/routes/session/undo.ts   | 14 +++++++
 packages/tui/test/cli/tui/undo.test.ts    | 48 +++++++++++++++++++++++
 3 files changed, 75 insertions(+), 7 deletions(-)
 create mode 100644 packages/tui/src/routes/session/undo.ts
 create mode 100644 packages/tui/test/cli/tui/undo.test.ts

diff --git a/packages/tui/src/routes/session/index.tsx b/packages/tui/src/routes/session/index.tsx
index ce99714ee81a..ffa1fee488df 100644
--- a/packages/tui/src/routes/session/index.tsx
+++ b/packages/tui/src/routes/session/index.tsx
@@ -84,6 +84,7 @@ import { usePathFormatter } from "../../context/path-format"
 import { useLocation } from "../../context/location"
 import { PluginSlot } from "../../plugin/render"
 import { usePlugin } from "../../plugin/context"
+import { undoMessage } from "./undo"
 import {
   cacheReuseDrop,
   createSessionRows,
@@ -656,19 +657,24 @@ export function Session() {
       group: "Session",
       slash: { name: "undo" },
       run: () => {
+        const admitted = pendingUsers().at(-1)
         const boundary = session()?.revert?.messageID
-        const message = messages().findLast(
-          (message): message is SessionMessageUser =>
-            message.type === "user" && !!message.text.trim() && (!boundary || message.id < boundary),
-        )
+        const message = admitted
+          ? { id: admitted.id, ...admitted.data }
+          : messages().findLast(
+              (message): message is SessionMessageUser =>
+                message.type === "user" && !!message.text.trim() && (!boundary || message.id < boundary),
+            )
         if (!message) {
           toast.show({ message: "Nothing to undo", variant: "error", duration: 3000 })
           dialog.clear()
           return
         }
-        void client.api.session.revert
-          .stage({ sessionID: route.sessionID, messageID: message.id })
-          .catch((error) => toast.show({ message: errorMessage(error), variant: "error", duration: 5000 }))
+        void undoMessage(client.api, {
+          sessionID: route.sessionID,
+          messageID: message.id,
+          pending: admitted !== undefined,
+        }).catch((error) => toast.show({ message: errorMessage(error), variant: "error", duration: 5000 }))
         prompt()?.set({
           ...projectedPromptInput(message),
           pasted: [],
diff --git a/packages/tui/src/routes/session/undo.ts b/packages/tui/src/routes/session/undo.ts
new file mode 100644
index 000000000000..6948405352fc
--- /dev/null
+++ b/packages/tui/src/routes/session/undo.ts
@@ -0,0 +1,14 @@
+import type { OpenCodeClient } from "@opencode-ai/client"
+
+export async function undoMessage(
+  client: OpenCodeClient,
+  input: { readonly sessionID: string; readonly messageID: string; readonly pending: boolean },
+) {
+  const revert = () => client.session.revert.stage(input).then(() => undefined)
+  if (!input.pending) return revert()
+
+  return client.session.pending.cancel({ sessionID: input.sessionID, inputID: input.messageID }).catch((error) => {
+    if (typeof error !== "object" || error === null || !("_tag" in error) || error._tag !== "ConflictError") throw error
+    return revert()
+  })
+}
diff --git a/packages/tui/test/cli/tui/undo.test.ts b/packages/tui/test/cli/tui/undo.test.ts
new file mode 100644
index 000000000000..7a8e1403f05d
--- /dev/null
+++ b/packages/tui/test/cli/tui/undo.test.ts
@@ -0,0 +1,48 @@
+import { expect, test } from "bun:test"
+import { OpenCode } from "@opencode-ai/client"
+import { undoMessage } from "../../../src/routes/session/undo"
+
+test.each([
+  { name: "projected", pending: false, cancelStatus: 204, expected: ["revert"] },
+  { name: "pending", pending: true, cancelStatus: 204, expected: ["cancel"] },
+  { name: "promoted race", pending: true, cancelStatus: 409, expected: ["cancel", "revert"] },
+])("undo routes $name messages", async ({ pending, cancelStatus, expected }) => {
+  const calls: string[] = []
+  const client = OpenCode.make({
+    baseUrl: "http://localhost:3000",
+    fetch: Object.assign(
+      async (input: URL | RequestInfo, init?: BunFetchRequestInit | RequestInit) => {
+        const request = input instanceof Request ? input : new Request(input, init)
+        const operation = request.method === "DELETE" ? "cancel" : "revert"
+        calls.push(operation)
+        if (operation === "cancel") {
+          if (cancelStatus === 409)
+            return Response.json({ _tag: "ConflictError", message: "Input was promoted" }, { status: 409 })
+          return new Response(null, { status: 204 })
+        }
+        return Response.json({ data: { messageID: "msg_user" } })
+      },
+      { preconnect: fetch.preconnect },
+    ),
+  })
+
+  await undoMessage(client, { sessionID: "ses_test", messageID: "msg_user", pending })
+
+  expect(calls).toEqual([...expected])
+})
+
+test("undo does not reinterpret transport failures as promotion races", async () => {
+  const client = OpenCode.make({
+    baseUrl: "http://localhost:3000",
+    fetch: Object.assign(
+      async () => {
+        throw new Error("offline")
+      },
+      { preconnect: fetch.preconnect },
+    ),
+  })
+
+  await expect(
+    undoMessage(client, { sessionID: "ses_test", messageID: "msg_user", pending: true }),
+  ).rejects.toMatchObject({ reason: "Transport" })
+})