Answer architecture round 1: List's walk and join sit in path.go, a compiled path's head is named head, every pick key comes from levelKeys, and readsColumn names all four readers

docs/comprehension-history.md

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+# Comprehension history
+
+## 2026-10-09T08:59:19Z, PR #190 at 17f732a, against ee4b40b
+
+Ruling: better
+
+| Seat | Vote |
+|---|---|
+| Mid A | better |
+| Inherited architect | better |
+
+Mid A, decided by:
+
+- `pick.go:9` `pickKey`: the definition sits on the type, beside `levelKeys`, `addressedKeys`, `keptInPick` and `readUnder`, where four files held them
+- `render.go:155` `readField`: one named predicate, `keptInPick`, states the whole keep rule
+- `datatype.go:217` `columnRead`: beside the code that reads it
+
+Inherited architect, decided by:
+
+- `pick.go:9` `pickKey`: the 3am path for a named pick now ends in one file, with its worked example
+- `render.go:155` `readField`: `keptInPick` holds its own nil and reference checks
+- `path.go:72` `compiledPath`: the field no longer reuses the vocabulary word level