Method getHistoryFromLatestBoundary

src/node/services/historyService.ts:959–1008

* Read messages from a compaction boundary onward. * Falls back to full history if no boundary exists (new/uncompacted workspace). * * @param skip How many boundaries to skip (counting from the latest, across * chat.jsonl and the sealed archive). 0 = read from the latest *

(workspaceId: string, skip = 0)

   * that only needs the active compaction epoch.
   */
  async getHistoryFromLatestBoundary(workspaceId: string, skip = 0): Promise<Result<MuxMessage[]>> {
    try {
      // One-time lazy migration: seal any pre-boundary prefix left in chat.jsonl
      // by older builds so this read (and every later one) stays O(active epoch).
      await this.ensureSealedHistoryRotated(workspaceId);

      const chatPath = this.getChatHistoryPath(workspaceId);
      const archivePath = this.getChatArchivePath(workspaceId);

      // Try the requested boundary in chat.jsonl, falling back to less-skipped boundaries.
      let chatBoundaryCount = 0;
      let chatFallbackOffset: number | null = null;
      for (let s = skip; s >= 0; s--) {
        const offset = await this.findLastBoundaryByteOffset(chatPath, s);
        if (offset !== null) {
          if (s === skip) {
            return Ok(await this.readHistoryFromOffset(chatPath, offset));
          }
          // chat.jsonl has fewer boundaries than requested; remember its oldest
          // boundary as a fallback and keep counting into the archive.
          chatBoundaryCount = s + 1;
          chatFallbackOffset = offset;
          break;
        }
      }

      // Boundaries older than chat.jsonl live in the sealed archive. A window that
      // starts at an archive boundary spans the archive tail plus all of chat.jsonl.
      for (let s = skip - chatBoundaryCount; s >= 0; s--) {
        const offset = await this.findLastBoundaryByteOffset(archivePath, s);
        if (offset !== null) {
          const archived = await this.readHistoryFromOffset(archivePath, offset);
          const active = await this.readChatHistory(workspaceId);
          return Ok([...archived, ...active]);
        }
      }

      if (chatFallbackOffset !== null) {
        return Ok(await this.readHistoryFromOffset(chatPath, chatFallbackOffset));
      }

      // No boundaries at all — workspace is uncompacted, full read is the only option
      const archived = await this.readArchivedHistory(workspaceId);
      const active = await this.readChatHistory(workspaceId);
      return Ok([...archived, ...active]);
    } catch (error) {
      const message = getErrorMessage(error);
      return Err(`Failed to read history from boundary: ${message}`);
    }
  }

  // ── Sealed-history rotation ─────────────────────────────────────────────
  // Compaction (and /clear --soft) appends a durable context boundary but, by