AO3-6272 Fix chapter count caching 0 after posting draft

[pmonfort]

Descripción:

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Issue

https://otwarchive.atlassian.net/browse/AO3-6272

Purpose

When posting a work from draft, the chapter count sometimes displays "0/1" instead of "1/1". This happens because number_of_posted_chapters uses Rails.cache.fetch, and the block inside it queries chapters.posted.count , which in production can hit a read replica that hasn't yet received the newly posted chapter. The stale 0 gets cached, and subsequent reads return the wrong count until the cache expires.

This PR writes the correct chapter count (1) directly to the cache immediately after saving in post_draft, so number_of_posted_chapters returns the cached value instead of querying a potentially stale replica.

Testing Instructions

This bug is not reproducible locally (no read replicas in development). The automated test simulates the stale replica by stubbing chapters.posted.count to return 0 and verifying that the cached value from post_draft takes precedence.

References

Related to AO3-6273 (word count blank after posting), which has a similar production environment but a different root cause.

Credit

Pablo Monfort (he/him)