Description

Implement durable fragment storage for AW fragments and embedded Wikifunctions fragments, replacing the current volatile Memcached backend with MainStash as the primary storage layer, so that cached fragments survive memory pressure and eviction cycles and readers see fewer unresolved placeholders.

This milestone covers:

• removing or reducing redundant orchestrator response storage under WikiLambdaFunctionCall,
• building date-aware static analysers (for both embedded and abstract wiki fragments) that can determine when fragments need to be daily re-rendered, or if they can be reused; this will drive TTL, key and location strategies; and
• implementing the AWFragmentStore and WikifunctionsClientStore interfaces against the agreed storage architecture.

Acceptance criteria:

This milestone is complete when:

• All subtasks are complete
• There's a clear and documented switchover path
• There are clear and documented observability tools

Completion checklist

• Before closing this task, review one by one the checklist available here: https://www.mediawiki.org/wiki/Abstract_Wikipedia_team/Definition_of_Done#Front-end_Task/Bug_Completion_Checklist