Method replaceHistory

src/node/services/workspaceService.ts:8067–8199

(
    workspaceId: string,
    summaryMessage: MuxMessage,
    options?: {
      mode?: "destructive" | "append-compaction-boundary" | null;
      deletePlanFile?: boolean;
    }
  )

  }

  async replaceHistory(
    workspaceId: string,
    summaryMessage: MuxMessage,
    options?: {
      mode?: "destructive" | "append-compaction-boundary" | null;
      deletePlanFile?: boolean;
    }
  ): Promise<Result<void>> {
    // Support both new enum ("user"|"idle") and legacy boolean (true)
    const isCompaction = !!summaryMessage.metadata?.compacted;
    if (!isCompaction) {
      const session = this.sessions.get(workspaceId);
      if (session?.isBusy() || this.aiService.isStreaming(workspaceId)) {
        return Err(
          "Cannot replace history while a turn is active. Press Esc to stop the stream first."
        );
      }
    }

    const replaceMode = options?.mode ?? "destructive";

    try {
      let messageToAppend = summaryMessage;
      let deletedSequences: number[] = [];

      if (replaceMode === "append-compaction-boundary") {
        assert(
          summaryMessage.role === "assistant",
          "append-compaction-boundary replace mode requires an assistant summary message"
        );

        // Only need the current epoch's messages — the latest boundary marker holds
        // the max compaction epoch, and epochs are monotonically increasing with
        // append-only compaction. Falls back to full history for uncompacted workspaces.
        const historyResult = await this.historyService.getHistoryFromLatestBoundary(workspaceId);
        if (!historyResult.success) {
          return Err(
            `Failed to read history for append-compaction-boundary mode: ${historyResult.error}`
          );
        }

        const nextCompactionEpoch = getNextCompactionEpochForAppendBoundary(
          workspaceId,
          historyResult.data
        );
        assert(
          isPositiveInteger(nextCompactionEpoch),
          "append-compaction-boundary replace mode must compute a positive compaction epoch"
        );

        const compactedMarker = isDurableCompactedMarker(summaryMessage.metadata?.compacted)
          ? summaryMessage.metadata.compacted
          : "user";

        messageToAppend = {
          ...summaryMessage,
          metadata: {
            ...(summaryMessage.metadata ?? {}),