Write-Path Dominance

Indexing is per turn and forever; the query is nearly free — which inverts every cost intuition carried over from retrieval.

Why it matters in a memory layer

Every message costs two model calls whether or not anyone ever asks a question about it, and that figure is linear in conversation length and independent of how much has been remembered. A year of use is arithmetic on message volume.

So the optimisation advice inverts too. Caching queries buys nothing when the read path makes no model calls; a cheaper extractor is the whole game; and deferring consolidation off the turn is worth measuring precisely because the expensive work is the work nobody is waiting for.

The read path being free is a design outcome rather than an optimisation. Arbitration refuses a model for explainability, ranking uses arithmetic for determinism, packing counts tokens because a budget is arithmetic — each argued on correctness grounds, with the cost profile as a side effect.

Connections

Taught in: The Write Path Dominates

Do not confuse with: Cost Profile