Hand the generated payload to the S3 cache write

[iHiD]

Each of the three S3 caches (Solution::CachedSerializedView, Concept::CachedContent, Exercise::CachedContent) generated its payload twice on every cache miss: once in Retrieve for the response, and again inside the deferred Store job in order to write it.

Retrieve now defers the write itself, passing the payload it has already built. That halves the work a miss costs, which matters most while a cache is cold and misses are the common case.

With the regeneration gone, Store did nothing beyond calling S3Cache::Write, so it's removed from all three.

The key is passed too, not recomputed

Worth a look in review, as it's a behaviour change rather than just a saving.

Store derived the cache key from the record it reloaded through its GlobalID, so it read whatever state that record was in when the job ran. If the record changed between the request and the job, the payload generated from the old version would be written under the new version's key — and then read back as if it were current.

Passing the key alongside the payload keeps the two on the same version by construction. The trade is that when a record does change mid-request, we now write an entry that is immediately superseded rather than opportunistically filling the new version's; the next read regenerates it. That seemed clearly preferable to being able to serve stale content.

Testing

• Replaced the Store unit tests with coverage on Retrieve: that a miss generates exactly once and hands that payload to the write, and that the write is keyed on the version that was serialized.
• test/commands/{solution/cached_serialized_view,concept/cached_content,exercise/cached_content,s3_cache} all pass; rubocop clean.
• test/controllers/tracks/community_solutions_controller_test.rb has 11 pre-existing asset-pipeline errors (The asset 'track.css' was not found in the load path) that reproduce identically on an unmodified main, so they're untouched by this.

🤖 Generated with Claude Code

https://claude.ai/code/session_01VDJXJXDiyrvKZBnXMuqGif