Function prepareCompactionMessage

src/browser/utils/chatCommands.ts:1519–1598

(options: CompactionOptions)

 * Returns the actual message text (summarization request), metadata, and options
 */
export function prepareCompactionMessage(options: CompactionOptions): {
  messageText: string;
  metadata: MuxMessageMetadata;
  sendOptions: SendMessageOptions;
} {
  // followUpContent is the content that will be auto-sent after compaction.
  // For forced compaction (no explicit follow-up), we inject a short resume sentinel ("Continue").
  // Keep that sentinel out of the *compaction prompt* (summarization request), otherwise the model can
  // misread it as a competing instruction. We still keep it in metadata so the backend resumes.
  // Only treat it as the default resume when there's no other queued content (images/reviews).
  //
  // Convert CompactionFollowUpInput to CompactionFollowUpRequest by adding model/agentId.
  // Compaction uses its own agentId ("compact") and potentially a different model for
  // summarization, so we capture the user's original settings for the follow-up message.
  //
  // In compaction recovery (retrying a failed /compact), followUpContent may already be
  // a CompactionFollowUpRequest with preserved model/agentId. Only fill in missing fields
  // to avoid overwriting the original settings when the user changes model/agent before retry.
  let fc: CompactionFollowUpRequest | undefined;
  if (options.followUpContent) {
    // Check if already a CompactionFollowUpRequest (has model/agentId from previous compaction)
    const existingModel =
      "model" in options.followUpContent &&
      typeof options.followUpContent.model === "string" &&
      options.followUpContent.model
        ? options.followUpContent.model
        : undefined;
    const existingAgentId =
      "agentId" in options.followUpContent &&
      typeof options.followUpContent.agentId === "string" &&
      options.followUpContent.agentId
        ? options.followUpContent.agentId
        : undefined;

    fc = {
      ...options.followUpContent,
      model: existingModel ?? options.sendMessageOptions.model,
      agentId: existingAgentId ?? options.sendMessageOptions.agentId ?? WORKSPACE_DEFAULTS.agentId,
      ...pickPreservedSendOptions(options.sendMessageOptions),
    };
  }

  // Build compaction message with optional continue context.
  // Shared helper is also used by backend-triggered idle compaction.
  const messageText = buildCompactionMessageText({
    maxOutputTokens: options.maxOutputTokens,
    followUpContent: fc,
  });

  // Handle model preference (sticky globally)
  const effectiveModel = resolveCompactionModel(options.model);

  const commandLine = formatCompactionCommandLine(options);
  const continueText = getFollowUpContentText(fc);
  const fullRawCommand = continueText ? `${commandLine}\n${continueText}` : commandLine;

  const compactData: CompactionRequestData = {
    model: effectiveModel,