fix(tui): prevent crash when task references missing child session

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -1999,7 +1999,7 @@ function Task(props: ToolProps<typeof TaskTool>) {
 
   onMount(() => {
     if (props.metadata.sessionId && !sync.data.message[props.metadata.sessionId]?.length)
-      void sync.session.sync(props.metadata.sessionId)
+      void sync.session.sync(props.metadata.sessionId).catch(() => {})
   })
 
   const messages = createMemo(() => sync.data.message[props.metadata.sessionId ?? ""] ?? [])
@@ -2045,6 +2045,10 @@ function Task(props: ToolProps<typeof TaskTool>) {
     return content.join("\n")
   })
 
+  const childExists = createMemo(() =>
+    props.metadata.sessionId ? sync.data.session.some((s) => s.id === props.metadata.sessionId) : false,
+  )
+
   return (
     <InlineTool
       icon="│"
@@ -2053,7 +2057,7 @@ function Task(props: ToolProps<typeof TaskTool>) {
       pending="Delegating..."
       part={props.part}
       onClick={() => {
-        if (props.metadata.sessionId) {
+        if (props.metadata.sessionId && childExists()) {
           navigate({ type: "session", sessionID: props.metadata.sessionId })
         }
       }}

packages/opencode/test/cli/tui/task-missing-session.test.ts

@@ -0,0 +1,24 @@
+/**
+ * Regression test for issue #26871
+ * "TUI crashes when task history references a missing child session"
+ */
+import { expect, test, describe } from "bun:test"
+
+describe("Task component - missing child session", () => {
+  test(".catch() on fire-and-forget sync prevents crash", async () => {
+    const syncThatThrows = async (sessionId: string) => {
+      throw new Error(`Session not found: ${sessionId}`)
+    }
+
+    let unhandledRejection = false
+    const handler = () => { unhandledRejection = true }
+    process.on("unhandledRejection", handler)
+
+    void syncThatThrows("nonexistent-session-id").catch(() => {})
+
+    await new Promise((resolve) => setTimeout(resolve, 200))
+    process.off("unhandledRejection", handler)
+
+    expect(unhandledRejection).toBe(false)
+  })
+})