refactor(playground): extract stream ready state checks

- move SSE ready-state status handling into stream utilities.
- keep weak source status typing outside the stream request hook.

web/default/src/features/playground/hooks/use-stream-request.ts

@@ -20,7 +20,11 @@ import { useCallback, useRef, useState } from 'react'
 import { SSE } from 'sse.js'
 import { getCommonHeaders } from '@/lib/api'
 import { API_ENDPOINTS, ERROR_MESSAGES } from '../constants'
-import { parseStreamErrorDetails, parseStreamMessageUpdates } from '../lib'
+import {
+  getStreamReadyStateError,
+  parseStreamErrorDetails,
+  parseStreamMessageUpdates,
+} from '../lib'
 import type { ChatCompletionRequest } from '../types'
 
 /**
@@ -99,14 +103,10 @@ export function useStreamRequest() {
       source.addEventListener(
         'readystatechange',
         (e: Event & { readyState?: number }) => {
-          const status = (source as unknown as { status?: number }).status
-          if (
-            e.readyState !== undefined &&
-            e.readyState >= 2 &&
-            status !== undefined &&
-            status !== 200
-          ) {
-            handleError(`HTTP ${status}: ${ERROR_MESSAGES.CONNECTION_CLOSED}`)
+          const errorMessage = getStreamReadyStateError(e.readyState, source)
+
+          if (errorMessage) {
+            handleError(errorMessage)
           }
         }
       )

web/default/src/features/playground/lib/stream-utils.ts

@@ -81,3 +81,21 @@ export function parseStreamMessageUpdates(data: string): StreamMessageUpdate[] {
 
   return updates
 }
+
+export function getStreamReadyStateError(
+  eventReadyState: number | undefined,
+  source: unknown
+): string | null {
+  const status = (source as { status?: number }).status
+
+  if (
+    eventReadyState !== undefined &&
+    eventReadyState >= 2 &&
+    status !== undefined &&
+    status !== 200
+  ) {
+    return `HTTP ${status}: ${ERROR_MESSAGES.CONNECTION_CLOSED}`
+  }
+
+  return null
+}