Add AGENTS.md and Ember Best Practices skill

.agents/skills/ember-best-practices/rules/exports-named-with-default-fallback.md

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+---
+title: Prefer Named Exports, Fallback to Default for Implicit Template Lookup
+impact: LOW
+impactDescription: Clear export contracts across .hbs and template-tag codebases
+tags: exports, hbs, gjs, interop, code-organization
+---
+
+## Prefer Named Exports, Fallback to Default for Implicit Template Lookup
+
+Use named exports for shared modules imported directly in JS/TS (utilities, constants, pure functions). If a module should be invokable from `.hbs` templates via implicit lookup, provide a default export. In hybrid `.gjs`/`.hbs` projects, a practical pattern is a named export plus a default export alias.
+
+**Incorrect (default export in a shared utility module):**
+
+```javascript
+// app/utils/format-date.js
+export default function formatDate(date) {
+  return new Date(date).toLocaleDateString();
+}
+```
+
+**Correct (named export in a shared utility module):**
+
+```javascript
+// app/utils/format-date.js
+export function formatDate(date) {
+  return new Date(date).toLocaleDateString();
+}
+```
+
+**Correct (hybrid `.gjs`/`.hbs` named export + default alias):**
+
+```javascript
+// app/helpers/format-date.js
+import { helper } from '@ember/component/helper';
+
+export const formatDate = helper(([value]) => {
+  return new Date(value).toLocaleDateString();
+});
+
+export default formatDate;
+```
+
+## Where Named Exports Are Preferred
+
+Use named exports when the module is imported directly by other modules and is not resolved via implicit template lookup.
+
+**Example (utility module with multiple named exports):**
+
+```javascript
+// app/utils/validators.js
+export function isEmail(value) {
+  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value);
+}
+
+export function isPhoneNumber(value) {
+  return /^\d{3}-\d{3}-\d{4}$/.test(value);
+}
+```
+
+Benefits:
+
+1. Explicit import contracts
+2. Better refactor safety (symbol rename tracking)
+3. Better tree-shaking for utility modules
+4. Easier multi-export module organization
+
+## Where Default Exports Are Required
+
+Use default exports for modules consumed through resolver/template lookup.
+If your project uses `.hbs`, invokables that should be accessible from templates should provide `export default`.
+In hybrid `.gjs`/`.hbs` codebases, use named exports plus a default export alias where you want both explicit imports and template compatibility.
+
+**Service:**
+
+```javascript
+// app/services/auth.js
+import Service from '@ember/service';
+
+export default class AuthService extends Service {
+  // ...
+}
+```
+
+**Route:**
+
+```javascript
+// app/routes/dashboard.js
+import Route from '@ember/routing/route';
+import { service } from '@ember/service';
+
+export default class DashboardRoute extends Route {
+  @service store;
+
+  model() {
+    return this.store.findAll('dashboard-item');
+  }
+}
+```
+
+**Modifier (when invoked from `.hbs`):**
+
+```javascript
+// app/modifiers/focus.js
+import { modifier } from 'ember-modifier';
+
+export default modifier((element) => {
+  element.focus();
+});
+```
+
+**Template (`.gjs`):**
+
+```glimmer-js
+// app/templates/dashboard.gjs
+<template>
+  <h1>Dashboard</h1>
+</template>
+```
+
+**Template (`.gts`):**
+
+```glimmer-ts
+// app/templates/dashboard.gts
+import type { TOC } from '@ember/component/template-only';
+
+interface Signature {
+  Args: {
+    model: unknown;
+  };
+}
+
+export default <template>
+  <h1>Dashboard</h1>
+</template> satisfies TOC<Signature>;
+```
+
+Template-tag files must resolve via a module default export in convention-based and `import.meta.glob` flows.
+For `app/templates/*.gjs`, the default export is implicit after compilation.
+
+## Strict Resolver Nuance
+
+With `ember-strict-application-resolver`, you can register explicit module values in `App.modules`:
+
+**Strict resolver explicit modules registration:**
+
+```ts
+modules = {
+  './services/manual': { default: ManualService },
+  './services/manual-shorthand': ManualService,
+};
+```
+
+In that explicit shorthand case, a direct value works without a default-exported module object.
+This is an explicit registration escape hatch and does not replace default-export requirements for `.hbs`-invokable modules.
+
+## Rule of Thumb
+
+1. If a module should be invokable from `.hbs`, provide a default export.
+2. In hybrid `.gjs`/`.hbs` projects, use named export + default alias for resolver-facing modules.
+3. Strict resolver explicit `modules` entries may use direct shorthand values where appropriate.
+4. Plain shared modules (`app/utils`, shared constants, reusable pure functions): prefer named exports.
+5. Template-tag components (`.gjs`/`.gts`): follow the component file-conventions rule and use named class exports.
+
+## References
+
+- [ES Modules Best Practices](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules)
+- [ember-strict-application-resolver](https://github.com/ember-cli/ember-strict-application-resolver)
+- [ember-resolver](https://github.com/ember-cli/ember-resolver)