Status: IN
Systems that route at write time push only lightweight references (post IDs, inbox pointers) and defer data hydration to reads — but these routing decisions are permanently locked in at write time with no retroactive correction mechanism, meaning a fast, cheap write path produces irrevocable outcomes.
Fan-out pushes references (lightweight) and routing decisions are permanent (binding) — the write path optimizes for speed at the cost of flexibility
Depends on (SL): fan-out-write-pushes-references-not-data, write-time-routing-is-irrevocable