docs: stub out guides for SchemaRecord, LinksMode, PolarisMode etc.

Author: runspired

guides/reactive-data/legacy/overview.md

@@ -0,0 +1,89 @@
+# LinksMode
+
+- ⮐ [Relationships Guide](../index.md)
+
+---
+
+**LinksMode** is a special feature that can be activated for any `belongsTo` or `hasMany` relationship.
+
+It allows that relationship to be fetched using the standard `request` experience instead of via the legacy `adapter` interface.
+
+LinksMode behaves *slightly* differently depending on whether
+you are using Model (including via [Legacy Mode](../../reactive-data/legacy/overview.md)) or [Polaris Mode](../../reactive-data/polaris/overview.md). We'll explain this nuance below.
+
+> [!TIP]
+> The next-generation of reactive data which replaces Model is SchemaRecord.
+> SchemaRecord has two modes, Legacy - which emulates all of Model's
+> behaviors and APIs, and Polaris - a new experience which we intend
+> to make default in Version 6.
+
+## Activating LinksMode
+
+#### For A Relationship on a Model
+
+Add `linksMode: true` to the relationship's options.
+
+```ts
+import Model, { belongsTo, hasMany } from '@ember-data/model';
+
+export default class User extends Model {
+  @belongsTo('address', {
+    async: false,
+    inverse: 'residents',
+    linksMode: true
+  })
+  homeAddress;
+}
+```
+
+This works for both `async` and `non-async` relationships and only changes the fetching behavior the field it is defined on. So for instance, in the example above, `homeAddress` is fetched in links mode while `<Address>.residents` might still be using the legacy adapter experience.
+
+#### For A SchemaRecord in LegacyMode
+
+```ts
+import type { ResourceSchema } from '@warp-drive/core-types/schema/fields';
+
+const UserSchema = {
+  type: 'user',
+  // this is what puts the record instance into legacy mode
+  legacy: true,
+  fields: [
+    {
+      kind: 'belongsTo',
+      name: 'homeAddress',
+      options: {
+        async: false,
+        inverse: 'residents',
+        linksMode: true
+      }
+    }
+  ]
+} satisfies ResourceSchema;
+```
+
+The behavior of relationships for a SchemaRecord in LegacyMode is always identical to that of Model's.
+
+#### For A SchemaRecord in PolarisMode
+
+```ts
+import type { ResourceSchema } from '@warp-drive/core-types/schema/fields';
+
+const UserSchema = {
+  type: 'user',
+  fields: [
+    {
+      kind: 'belongsTo',
+      name: 'homeAddress',
+      options: {
+        async: false,
+        inverse: 'residents',
+        linksMode: true
+      }
+    }
+  ]
+} satisfies ResourceSchema;
+```
+
+The only difference here is that we don't mark the resource schemas as `legacy`. This puts us in the standard/default mode (`polaris`);
+
+Async relationships are not supported in Polaris mode!

guides/reactive-data/polaris/overview.md

@@ -0,0 +1,5 @@
+# Relationship Polymorphism
+
+- ⮐ [Relationships Guide](../index.md)
+
+---

guides/relationships/features/links-mode.md

@@ -2,6 +2,9 @@
 
 ## Feature Overview
 - [Inverses](./features/inverses.md)
+- [LinksMode](./features/links-mode.md)
+- [Polymorphism](./features/polymorphism.md)
+
 <!--
 - [Resource Relationships]()
 - [Collection Relationships]()