Method createBranchSession

packages/runtime/src/session-manager.ts:4997–5043

(
    sessionId: string,
    sourceView: RuntimeReadModelSessionView,
    copied: StoredMessage[],
    input: BranchFromTurnInput,
  )

  }

  private async createBranchSession(
    sessionId: string,
    sourceView: RuntimeReadModelSessionView,
    copied: StoredMessage[],
    input: BranchFromTurnInput,
  ): Promise<SessionSummary> {
    const plan = await this.prepareConversationRuntimeLedgerClone(sessionId, sourceView, copied);
    const [header, boundary] = await Promise.all([
      this.deps.store.readHeader(sessionId),
      this.deps.store.readExecutionBoundary(sessionId),
    ]);
    const next = await this.deps.store.create(
      {
        cwd: header.cwd,
        ...(header.projectId !== undefined ? { projectId: header.projectId } : {}),
        backend: header.backend,
        llmConnectionSlug: header.llmConnectionSlug,
        model: header.model,
        thinkingLevel: header.thinkingLevel,
        permissionMode: header.permissionMode,
        collaborationMode: header.collaborationMode,
        orchestrationMode: header.orchestrationMode ?? 'default',
        name: input.name ?? `${header.name} · 分支`,
        labels: input.sideConversation
          ? [...new Set([...header.labels, SIDE_CONVERSATION_SESSION_LABEL])]
          : header.labels,
        parentSessionId: sessionId,
        branchOfTurnId: input.sourceTurnId,
        status: 'active',
      },
      boundary,
    );
    try {
      const rewritten = await this.cloneConversationRuntimeLedger(next.id, copied, plan);
      if (rewritten.length > 0) await this.deps.store.appendMessages(next.id, [...rewritten]);
      await this.deps.store.appendMessage(next.id, {
        type: 'system_note',
        id: this.deps.newId(),
        ts: this.deps.now(),
        kind: 'session_start',
        data: { parentSessionId: sessionId, branchOfTurnId: input.sourceTurnId },
      });
      return headerToSummary(await this.deps.store.readHeader(next.id));
    } catch (error) {
      return this.rollbackLegacyConversationCopy(next.id, error);
    }
  }

  async respondToSandboxBoundary(
    sessionId: string,