fix(client): lint:layers holds src/types.ts to the rules of types

A file's layer was the first path segment under src/, so src/types.ts,
the shared types module every layer imports as '../types', got the
layer "types.ts" and no rule at all, while the imports into it already
resolved to "types". It could import a component or a page unnoticed.
A file directly in src/ is now the layer of its name without the
extension, for the importer and the import alike. No file changes its
count: types.ts imports only @trek/shared today.

client/scripts/lib/imports.mjs

@@ -53,9 +53,19 @@ export function importsOf(source, file) {
 }
 
 /**
- * The top directory under src/ a relative import lands in ("components",
- * "api"; a file directly in src/ gives its own name), or null for a package
- * or a path outside src/.
+ * The layer of a path from src/: its top directory ("components", "api"), or,
+ * for a file directly in src/, its name without the extension. src/types.ts
+ * is then the layer "types" both when it imports and when it is imported as
+ * '../types', and its rules are those of the src/types/ directory.
+ */
+export function layerOfPath(fromSrc) {
+  const [top, ...rest] = fromSrc.split('/');
+  return rest.length ? top : top.replace(/(\.d)?\.[cm]?[jt]sx?$/, '');
+}
+
+/**
+ * The layer a relative import lands in (see layerOfPath), or null for a
+ * package or a path outside src/.
  */
 export function layerOf(srcRoot, fromFile, specifier) {
   if (!specifier.startsWith('.')) return null;
@@ -63,7 +73,7 @@ export function layerOf(srcRoot, fromFile, specifier) {
     .split('\\')
     .join('/');
   if (!target || target.startsWith('..')) return null;
-  return target.split('/')[0];
+  return layerOfPath(target);
 }
 
 /** Every source file under root/src outside the tests, with its key, its layer and its imports resolved to layers. */
@@ -71,7 +81,7 @@ export function sourceGraph(root) {
   const src = join(root, 'src');
   return listFiles(root, ['src'], (key) => /\.tsx?$/.test(key) && !TEST_FILE.test(key)).map((path) => ({
     key: toKey(root, path),
-    layer: toKey(src, path).split('/')[0],
+    layer: layerOfPath(toKey(src, path)),
     imports: importsOf(readText(path), path).map((imp) => ({ ...imp, layer: layerOf(src, path, imp.specifier) })),
   }));
 }

client/scripts/lib/layers.mjs

@@ -17,7 +17,8 @@ const VIEW = ['components', 'mobile', 'pages', 'hooks'];
  * (date helpers) are helpers like utils/. Directories without an entry are
  * free on purpose: mobile and pages sit at the top, the app root wires
  * everything, and managed/ is the slot an operator fills with whole screens
- * at build time.
+ * at build time. A file directly in src/ is the layer of its name, so
+ * src/types.ts falls under types like the src/types/ directory.
  */
 export const RULES = {
   components: ['pages', 'mobile'],