refactor(chat): split stream helpers

src/routes/chatSession.ts

@@ -4,6 +4,7 @@ import { MemoryStore } from "../memory/store.js";
 import { type OpencodeRuntimeAdapter } from "../runtime/opencode.js";
 
 import { collectTextContent } from "./chatStream.js";
+import { isPressureTrendDemoPrompt } from "./pressureTrendDemo.js";
 
 const TITLE_PROMPT_TIMEOUT_MS = 5000;
 const TITLE_CONTEXT_MESSAGE_LIMIT = 40;
@@ -217,6 +218,35 @@ export const shouldRestoreConversationForRuntime = (options: {
   runtimeHasConversation: boolean;
 }) => !options.hadExistingSessionRecord || !options.runtimeHasConversation;
 
+export const buildForkedSessionUiState = (
+  sourceState: { messages?: unknown[] } | null | undefined,
+  input: {
+    keepMessageCount: number;
+    targetSessionId: string;
+  },
+) => ({
+  sessionId: input.targetSessionId,
+  isTitleManuallyEdited: false,
+  messages: Array.isArray(sourceState?.messages)
+    ? sourceState.messages.slice(0, input.keepMessageCount)
+    : [],
+});
+
+export const resolveRequestedStreamSessionId = (input: {
+  sessionId?: string;
+  promptText: string;
+  createClientSessionId: () => string;
+}) => {
+  const sessionId = input.sessionId?.trim();
+  if (sessionId) {
+    return sessionId;
+  }
+  if (isPressureTrendDemoPrompt(input.promptText)) {
+    return input.createClientSessionId();
+  }
+  return undefined;
+};
+
 const buildRestoredConversationContext = (recentTurns: SessionTurnRecord[]) => {
   const formattedTurns = recentTurns
     .slice(-RESTORE_TURN_LIMIT)