Answer architecture round 1: a module's reads sits on its index entry or, for a source without an index, in the load that walks it, the note names default modules, the shipped modules are listed by name, datafiles drops its unused base, and item 195 files the builtins' second parse

docs/decisions.md

@@ -143,7 +143,7 @@ package under `data/` embeds its own files, and a library imports the packages i
 
 - One Go package per locale, one per country's `geo/` tree, and one for `misc`, all in the core's Go module. A package registers nothing when imported.
 - A bare `New()` loads no data and fails, naming the option to add. `WithoutShippedData` goes.
-- A data package's `FS` is an `fs.FS` passed to `WithDataFS`, as anyone's data is, and `New` takes several. A module carrying functions loads through an option of its own, so a data module that starts carrying functions breaks its users. Such a function reaches the randomness through an interface the root declares; `internal/drawstate`'s type stays internal.
+- A data package's `FS` is an `fs.FS` passed to `WithDataFS`, as anyone's data is, and `New` takes several. It is an exported `var FS embed.FS`, the shape `//go:embed` gives; a function returning it would guard only against a program reassigning a dependency of its own. A module carrying functions loads through an option of its own, so a data module that starts carrying functions breaks its users. Such a function reaches the randomness through an interface the root declares; `internal/drawstate`'s type stays internal.
 - A module names, in a manifest, every module it reads by default, directly or through another, so the first error names the whole set to import. A manifest is optional: a `--data-path` folder without one is a module. Nothing loads a default on its own.
 - A manifest names no fejkdata version, and `New` checks none: the shipped packages ship in the core's Go module, and a module from anyone else keeps loading across a minor or a patch, as the README's Versioning promises. The maintainer chose so on 2026-10-09.
 - In the CLI, a flag of its own says a `--data-path` replaces what it clashes with, so flags still go anywhere on the line. Data authors and hand fixture authors bench it.
@@ -582,7 +582,9 @@ when a source carries it.
 
 2026-09-24, Lilleman auf Larv; revised 2026-10-10, when the shipped data became Go packages.
 Serves goal 6.2. `sv_SE.FS` loads alone, and `sv_SE.address` then fails at first reach,
-naming `github.com/larvit/fejkdata/data/geo/SE`, which `sv_SE`'s manifest reads.
+naming `github.com/larvit/fejkdata/data/geo/SE`, which `sv_SE`'s manifest reads. `New`
+checks no `reads`: a stand-in providing the same paths under another name would fail it
+(goal 9.2).
 `--no-shipped-data -d` takes a locale's folder with its country's, or a set of one's own.
 
 ## The default embed holds every Swedish postort the import can place and give a street-delivery code and a street, and the US places of 25,000 or more