effect-v4-module-index

The routing map for Effect v4 core — every module in one table, what it is, when to reach for it, and where to read it in the vendored source. Use FIRST when asking "what module do I reach for", "does Effect have a Sink/Pool/Trie/pattern-matcher", "what is Sink/Channel/Deferred/RcMap for", "where does X live in the source", or before designing ANY capability (the contract-inventory gate greps this map's territory). Opens with a routing-by-task table for the ones people miss by name — spawning a subprocess, a TTL cache with in-flight de-duplication, writing to stdout from a library. Rows route; they do not teach — patterns live in the other effect-v4-* skills, and the source is the authority on signatures and semantics.