EditingsController#index N+1 queries via fetch_cache — cache cold overlay

Completeness#

#	Plan Item	Status	Evidence
1	`fetch_cache_multi` method added to `Cachable`	PASS	`app/models/concerns/cachable.rb`: lines 76-108 add `fetch_cache_multi(model_name, ids)` method using `Rails.cache.fetch_multi`
2	`fetch_cache` instrumentation with `ActiveSupport::Notifications.instrument`	PASS	`app/models/concerns/cachable.rb`: lines 73-74 add `ActiveSupport::Notifications.instrument('cache.fetch_cache', model: model_name, hit: hit)` after cache fetch
3	`EditingSerializer.prefetch_caches` class method	PASS	`app/serializers/editing_serializer.rb`: lines 14-27 add `self.prefetch_caches(records)` class method that collects association IDs and calls `fetch_cache_multi`
4	`editing_repository.rb` `default_joins` includes eager loading	PASS	`app/repositories/editing_repository.rb`: line 190 adds `.includes(:user, :editor, :escalated_by, :level, :category, :workarea, :record, :team, :workspace, :facility)`

Acceptance Criteria#

#	Criterion	Status	Evidence
1	`Cachable` module has `fetch_cache_multi(model_name, ids)` public instance method	PASS	`app/models/concerns/cachable.rb`: lines 76-108 define `def fetch_cache_multi(model_name, ids)` as a public method within the module
2	`fetch_cache_multi` uses `Rails.cache.fetch_multi` for batch lookup	PASS	`app/models/concerns/cachable.rb`: line 82 calls `Rails.cache.fetch_multi(*keys, expires_in: self.class.cache_expires_in)`
3	`fetch_cache` has `ActiveSupport::Notifications.instrument('cache.fetch_cache', ...)`	PASS	`app/models/concerns/cachable.rb`: line 73 instruments `'cache.fetch_cache'` with `model:` and `hit:` payload
4	`EditingSerializer` has `prefetch_caches` method callable in collection mode	PASS	`app/serializers/editing_serializer.rb`: lines 14-27 define `self.prefetch_caches(records)` and `app/controllers/api/v1/editings_controller.rb`: line 15 calls `EditingSerializer.prefetch_caches(editings.contents)`
5	`editing_repository.rb` `default_joins` has `includes` or `preload` added	PASS	`app/repositories/editing_repository.rb`: line 190 adds `.includes(...)` with all required associations
6	All changed files pass `ruby -c` syntax validation	PASS	Additional context confirms all 4 files passed `ruby -c` syntax validation

Issues Found#

No blocking issues found.

Observations#

Controller change not in plan: app/controllers/api/v1/editings_controller.rb was modified to call EditingSerializer.prefetch_caches(editings.contents). While this file was not explicitly listed in the plan's "Changes" section, it is a logical necessity -- the prefetch_caches method must be invoked somewhere before serialization. The plan's acceptance criterion #4 states "collection mode invocation" which implies a call site. This is a reasonable addition.
Cache hit/miss counting in fetch_cache_multi: The hit/miss detection (lines 90-99) uses value.nil? to determine misses. If a cache entry legitimately stores nil (e.g., a record that does not exist), it would be counted as a miss. However, given the skip_nil: true option used in fetch_cache, this pattern is consistent with existing behavior where nil values are not cached.
Thread safety of prefetch_caches: The prefetched results go into Rails.cache (shared cache store), so subsequent fetch_cache calls on individual records will naturally find them. This is a clean approach that does not require thread-local storage, contrary to what the plan mentioned. The implementation is simpler and equally correct.
Eager loading scope: The includes in default_joins adds :team, :workspace, :facility which were already in the original left_joins call, plus new associations. The original left_joins is retained alongside includes, which may result in duplicate JOIN clauses for some associations. Rails typically handles this gracefully, but monitoring query plans in production would be prudent.