Retain content-validated message fragments across unrelated commits

app/models/fragment_cache.rb

@@ -1,5 +1,12 @@
 # Native view caches share one byte budget across every database generation.
 class FragmentCache
+  # Only callers that fingerprint every rendered dependency may omit the epoch.
+  ContentKey = Data.define(:digest) do
+    def cache_key
+      digest
+    end
+  end
+
   STORE = ActiveSupport::Cache::MemoryStore.new(size: 64.megabytes)
   private_constant :STORE