What is built: Project layout and modules

The compiler builds the decided layout, with each rule's real output under Errors.

Feature	Status
Root, domains and their folders	Built: a file where the layout has no place for it is `layout.unknown_location`, and a declaration in the wrong folder `layout.wrong_folder`; a folder or file with no `app.jadpo` above it is checked as loose files. Not built yet: `jadpo domain rename`, `split` and `merge`; the `documents` capability, so a file in `documents/` is `layout.unknown_location` until it is.
Files and names	Built: one primary declaration per file, named after it; names unique project-wide; the round-trip and folded-collision rules, with the exception for a type folding to its callable's name.
Names per domain	Partly built: private functions and types unique only within their domain, each domain's code reading its own; their identity keys carrying the domain, with promotion to `shared/` writing a registry line; `semantic.duplicate_declaration` saying copy or clash and listing the names in use with the same words. `jadpo rename` is not built yet (Commands for looking into and changing code).
Order independence	Built: declaration and file order never matter.
Domains, `public` and calls	Built: owner-qualified calls and per-declaration `public`, with `visibility.private_cross_domain`, `visibility.public_not_allowed` and `visibility.public_unused`.
Reserved words	Built: a reserved word can't name anything.
Comments	Built: `//` and `///` documentation comments.
Similar helpers	Built: `library.similar_exists`, a declinable error. Not built yet: `jadpo impact`.
Declinable errors	Partly built: no warning severity; the `decline <rule>: "<reason>"` line with `decline.unused`, `decline.not_declinable` and `decline.no_reason`; `jadpo declines list` and `clear`; the editor's "Decline with a reason" and "Remove decline". Not built yet: `jadpo approval` (Records and manifest) and the date rule for expired feature flags.
Constants	Built: `constant` as a reserved word and a declaration placed and shared as helper functions are, a private one unique within its domain, `constant.similar_exists`, and a top-level `var` pointed at `constant` (Constants).
Imports	Built: `use <folder> { Names }` and `use <domain>`, with `import.missing`, `import.unknown`, `import.unused`, `import.unneeded` and `import.duplicate`; `jadpo fmt` adds, removes and sorts imports, `jadpo fmt --layout` makes promotion moves, and go to definition works from every use of a name, a `use` line's included.
A file holds only what its primary declaration uses	Built: `layout.unused_declaration` for a supporting declaration the primary declaration doesn't use, directly or through one another.
Definition before use	Built: `jadpo fmt` writes each file's declarations before the first one that uses them, and `jadpo fmt --check` fails on a file out of that order.
Referenced assets	Not built yet: `layout.asset_unreferenced` waits for the ways Integrations and Built-in services refer to files that aren't Jadpo.
Jadpo version	Built: `application { jadpo: "0.1" }`, with `toolchain.version_newer` refusing a project on a later line, `toolchain.version_older` one on an earlier line, each naming the release to install, and `toolchain.version_invalid`; the installed `jadpo` runs the release the line or `jadpo.lock`'s pin names (Which jadpo runs). `jadpo new` writes the line of the `jadpo` that ran it.
Packages	Built: the root `packages/` and `jadpo.lock`, `shared/providers/`, packages checked as `shared/` is, `use packages/<name>`, and the reachable-from-public rule (`visibility.public_reaches_private`) in domains and packages; Integrations records the choices.

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