fix(tui): guard messages.data in session.sync against undefined (#26566)

Co-authored-by: Developer <temp@example.com>

packages/opencode/test/cli/cmd/tui/sync-undefined-messages.test.tsx

@@ -0,0 +1,47 @@
+/** @jsxImportSource @opentui/solid */
+/**
+ * Reproducer for #26560 — TUI crashes with
+ *   `TypeError: undefined is not an object (evaluating 'f.data.map')`
+ * when entering a session whose messages endpoint returns a non-2xx.
+ * The failure path is `sync.tsx#sync.session.sync` reading
+ * `messages.data!` while the SDK leaves `data` undefined on error.
+ */
+import { describe, expect, test } from "bun:test"
+import { Global } from "@opencode-ai/core/global"
+import { tmpdir } from "../../../fixture/fixture"
+import { directory, json, mount } from "./sync-fixture"
+
+const sessionID = "ses_undef"
+
+describe("tui sync (#26560)", () => {
+  test("entering a session whose messages endpoint errors does not crash sync", async () => {
+    const previous = Global.Path.state
+    await using tmp = await tmpdir()
+    Global.Path.state = tmp.path
+    await Bun.write(`${tmp.path}/kv.json`, "{}")
+
+    const sessionPayload = {
+      id: sessionID,
+      title: "broken",
+      time: { created: 0, updated: 0 },
+      version: "1.14.42",
+      directory,
+      project_id: "proj_test",
+    }
+    const { app, sync } = await mount((url) => {
+      if (url.pathname === `/session/${sessionID}`) return json(sessionPayload)
+      if (url.pathname === `/session/${sessionID}/messages`) return json({}, { status: 500 })
+      if (url.pathname === `/session/${sessionID}/todo`) return json([])
+      if (url.pathname === `/session/${sessionID}/diff`) return json([])
+      if (url.pathname === "/session") return json([sessionPayload])
+      return undefined
+    })
+
+    try {
+      await expect(sync.session.sync(sessionID)).resolves.toBeUndefined()
+    } finally {
+      app.renderer.destroy()
+      Global.Path.state = previous
+    }
+  })
+})