[Bug]: Ghost view rows persisting after their corresponding docs have been purged

The issue includes a detailed reproduction script. Start by running the script to confirm the ghost rows. Examine the view indexing logic in the CouchDB source, likely in the view server or indexer modules. Look for how purges interact with view updates. The goal is to understand why rows persist after purges and ensure they are cleaned up during normal operations.

Version

3.5.2

Describe the problem you're encountering

I am seeing view row ghosts when I purge large amounts of documents, while querying the view in between purge batches. These ghost rows return doc: null when queried with include_docs=true, and they never go away, they survive new docs being pushed and compaction. Only a full index rebuild seems to remove them.
The view reports that it caught up with the purges.

Expected Behaviour

I would expect the view to never return rows with no docs, or at least to heal after some point.

Steps to Reproduce

Repro script available here: https://gist.github.com/dianabarsan/5e21753d6545e6f61429ed31ebe79714

• create throwaway db
• create one design doc and one view that would index every doc
• seed db with 300k documents
• with a batch size of 1000, purge all documents, querying the view after each batch
• after all docs are purged, query the view and inspect the results

Sample result:

CouchDb 3.5.2, 300000 docs, purging 1000 at a time, querying view after each batch

attempt 1:     543 ghost view rows

db doc_count   0
db purge_seq   300000-g1AAAAIdeJx90C0OwkAQBeAJIDEILoEgFIOEGxBo5wD9Ec2mgYQEjeIIlVhoh-BxgOAACDgEZ6BdZqd-dsUT871NZjMA6KbtBHrxehunSTTzxpPhiK-X8ai16sCJ6Mth-ZgIIHzqfIn45jhyS_he55W1N44Ft4RvdF4QEcePW8LnOvcR82YFEn5ReLSztm4WyAXfNWyISteohL40ioiB84XQq0an_MnO-0LPGh3wTs7XQg8a7fOLzpdCPwoNweFA3MP8AXUdop0
view purge_seq 300000
view query result:
{
  total_rows: 543,
  offset: 0,
  rows: [
    { id: 'd32020', key: 'd32020', value: null, doc: null },
    { id: 'd32024', key: 'd32024', value: null, doc: null },
    { id: 'd32028', key: 'd32028', value: null, doc: null },
    { id: 'd32034', key: 'd32034', value: null, doc: null },
    { id: 'd32069', key: 'd32069', value: null, doc: null },
    { id: 'd32071', key: 'd32071', value: null, doc: null },
    { id: 'd32075', key: 'd32075', value: null, doc: null },
    { id: 'd32079', key: 'd32079', value: null, doc: null },
    { id: 'd32092', key: 'd32092', value: null, doc: null },
    { id: 'd32096', key: 'd32096', value: null, doc: null },
    ... 533 more items
  ]
}

What I see in Fauxton:

https://github.com/user-attachments/assets/caec4929-ebe1-4910-bc5b-d566e31ad6a4

Your Environment

Manjaro Linux, CouchDb 5.3.2 in Docker

Additional Context

No response