Hybrid Cache: Clear published content cache on content type change

[AndyButland]

Issue

I found this issue when testing the results of performance improvements for save of content types in #21207, but as it's a clear regression in 17 we should look to review and release it earlier.

To reproduce:

• Have a rendered document using InMemoryAuto for models builder.
• Save the document type the document is based on on the backoffice.
• Refresh the rendered page and note a null reference exception error.
• Clearing the memory cache or database cache doesn't help, it's only a restart that allows the page to render correctly again,

Cause

• The root cause is that the _publishedContentCache (introduced in Performance: Cache published content instances at cache service level #20681) caches IPublishedContent objects which hold references to IPublishedContentType. When a content type is modified, these cached objects become stale.
• The fix clears the entire _publishedContentCache at the end of the Rebuild method in both DocumentCacheService and MediaCacheService

Technical Details

The _publishedContentCache is a ConcurrentDictionary<string, IPublishedContent> that caches fully-constructed IPublishedContent objects for performance. However, these objects contain references to their IPublishedContentType, which becomes stale when the content type is modified.

A filtered/targeted clear approach was attempted but has inherent race conditions due to the non-atomic check-then-act pattern. I was also concerned that content types can be used in various places in a document (elements, compositions etc.). So the atomic Clear() looks to be the only reliable solution.

Test plan

• Save a document type that has existing documents
• Verify documents based on that type render correctly without restart

🤖 Generated with Claude Code with human updates.

[Copilot]

Pull request overview

This PR fixes an issue where saving a document type causes documents based on that type to show null model errors in Razor rendering. The root cause is that the _publishedContentCache caches IPublishedContent objects which hold references to IPublishedContentType. When a content type is modified, these cached objects become stale and must be cleared.

Key Changes

• Adds _publishedContentCache.Clear() at the end of the Rebuild method in DocumentCacheService to clear stale published content when document types change
• Adds the same cache clearing logic to MediaCacheService to handle media type changes

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Umbraco.PublishedCache.HybridCache/Services/DocumentCacheService.cs	Clears the entire published content cache after rebuilding when document types are modified
src/Umbraco.PublishedCache.HybridCache/Services/MediaCacheService.cs	Clears the entire published content cache after rebuilding when media types are modified

[Zeegaan]

This makes sense to me, we should really be looking into not having the _publishedContentCache, and instead entirely caching IPublishContent via the hybrid cache instead, this might cause som breaking changes, but effectively we're double caching published content, just to avoid having to rebuild from the factory every time, which is not ideal 🙈

[Zeegaan]

Cherry picked for 17.1 🍒