fix(slack): swapped checkpoint index

[jessicasingh7]

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Project	Deployment	Preview	Comments	Updated (UTC)
internal-search	Ready	Preview	Comment	Sep 16, 2025 11:43pm

[greptile-apps]

Greptile Summary

This PR fixes a critical bug in the Slack connector's checkpoint handling that was causing incorrect message retrieval boundaries during incremental indexing. The fix involves two key corrections in the _get_all_doc_ids method:

1. Line 840: Changed latest = channel_message_ts to oldest = channel_message_ts when loading from checkpoint
2. Line 858: Changed message_batch[-1]["ts"] to message_batch[0]["ts"] when determining the new checkpoint timestamp

The root cause was a misunderstanding of Slack's API behavior and checkpoint semantics. Slack's API returns messages from newest to oldest, so when resuming from a checkpoint, the stored timestamp represents the oldest message previously processed. The connector should continue from this point by setting oldest = channel_message_ts, not latest. Similarly, when updating the checkpoint for the next run, it should use the timestamp of the first (newest) message in the batch, not the last (oldest).

This bug would have caused either message gaps (missing messages between runs) or duplicates during incremental indexing, which is critical for maintaining search index consistency. The fix aligns the implementation with the documented API behavior and ensures proper checkpoint-based message retrieval.

Confidence score: 5/5

• This PR is extremely safe to merge with virtually no risk of causing issues
• Score reflects a simple but critical bug fix with clear logic and minimal scope of change
• No files require special attention as the changes are straightforward and well-targeted

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[cubic-dev-ai]

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