Add "Projects" page, improve Subproject discoverability

fern/products/platform/pages/getting-started.mdx

@@ -272,6 +272,20 @@ const client = RestClient(PROJECT_ID, API_TOKEN, {
 
 ## Core concepts
 
+### Projects and Subprojects
+
+A **Project** groups everything you build: phone numbers, Resources, and API credentials.
+Every Space starts with one, and you can add more at any time.
+
+Beneath a Project you can nest **Subprojects**, one level deep.
+A Subproject is a full Project with its own Project ID, API tokens, and Resources, which makes it
+the way to isolate a customer, a tenant, or a staging environment.
+Unlike root Projects, Subprojects can be created and deleted through the API.
+
+<Card title="Learn more about Projects" href="/docs/platform/projects" horizontal>
+  What a Project scopes, and how Subprojects nest beneath one
+</Card>
+
 ### Communication channels
 
 SignalWire supports the following communication channels:
@@ -329,21 +343,21 @@ We also offer the option of purchasing phone numbers programmatically via our [P
 In SignalWire, a **Resource** is anything that can handle communications - an AI agent, a script, a SIP connection, or your own application.
 When a call or message comes in, you tell SignalWire which Resource should handle it.
 
-Common resource types include:
+Common Resource types include:
 - **SWML Scripts** - Simple JSON/YAML instructions hosted in your Dashboard
 - **AI Agents** - Conversational AI that handles calls autonomously
 - **Call Flows** - Visual drag-and-drop call routing
 - **Relay Applications** - Your own server applications connected via WebSocket
 
 <Card title="Learn more about Resources" href="/docs/platform/resources" horizontal>
-  Understanding the different resource types
+  Understanding the different Resource types
 </Card>
 
 ### Addresses
 
 Every Resource has an **Address**.
 This is a unique identifier that lets you target and interact with it.
-Think of addresses as the **phone number** for any resource, but broader in scope.
+Think of addresses as the **phone number** for any Resource, but broader in scope.
 
 Addresses can be:
 - **Phone numbers** - Traditional numbers like `+14155551234` for PSTN calls

fern/products/platform/pages/platform/core/projects.mdx

@@ -0,0 +1,99 @@
+---
+title: Projects
+description: Projects group the phone numbers, Resources, and credentials in your Space, and Subprojects nest one level beneath a root Project with their own Project ID and Resources.
+slug: /projects
+max-toc-depth: 3
+---
+
+A Project is the container for what you build in a SignalWire Space.
+Phone numbers, [Resources](/docs/platform/resources), and
+[API credentials](/docs/platform/your-signalwire-api-space) all belong to exactly one Project,
+which is how you group work by customer, by environment, or by any other classification you like.
+
+Your Space starts with one Project, created alongside the Space itself, and you can add more
+from your Dashboard at any time.
+
+## What a Project scopes
+
+Each Project carries its own Project ID and its own API tokens, and every request you make is
+authenticated as one Project and acts on that Project alone.
+
+Security settings belong to the Project too.
+Each Project has its own [media URL protection](/docs/platform/media-protection) settings for
+recordings, message media, and fax media, and its own choice of whether webhooks and callbacks
+must use HTTPS.
+
+Not everything divides along Project lines.
+Voice and messaging [rate limits](/docs/platform/rate-limits) are account-level, counted across
+every Project in your Space.
+
+## Subprojects
+
+A Subproject is a Project nested one level beneath a root Project.
+It is a full Project with its own Project ID and Resources, but a Subproject cannot contain other
+Subprojects.
+
+Unlike root Projects, Subprojects can be created and deleted through the
+[Projects API](/docs/apis/rest/projects/list-projects), so an application can open and retire a
+Project per customer, per tenant, or per environment on its own.
+Root Projects are created in the Dashboard and can't be deleted through the API.
+
+### Create a Subproject
+
+Authenticate as the root Project and send the Subproject's name, along with any security settings
+you want it to start with.
+A Subproject cannot create another Subproject, so a request authenticated as a Subproject fails
+with `422 nested_subprojects_not_allowed`.
+
+<EndpointRequestSnippet endpoint="POST /api/projects" />
+
+The response is the only place the new Project's `signing_key` appears — it can't be retrieved
+afterward, so capture it here.
+
+<EndpointResponseSnippet endpoint="POST /api/projects" />
+
+To get credentials for the new Subproject, call
+[Create API token](/docs/apis/rest/project-tokens/create-token) from the root Project with the
+Subproject's ID in `subproject_id`.
+
+### Delete a Subproject
+
+Only Subprojects can be deleted through the API; targeting the root Project returns
+`422 only_subprojects_can_be_deleted`.
+
+<Warning title="Release phone numbers first">
+
+A Project must have no phone numbers before it can be deleted, or the request returns
+`422 phone_numbers_must_be_removed`.
+Deleting a Subproject also migrates its registry brands and campaigns up to the parent Project.
+
+</Warning>
+
+<EndpointRequestSnippet endpoint="DELETE /api/projects/{id}" />
+
+## Manage Projects through the API
+
+Every Projects API request reaches only the authenticated Project and the Subprojects beneath it.
+[List projects](/docs/apis/rest/projects/list-projects) returns the authenticated Project
+alongside its Subprojects, and each entry reports whether it is a Subproject and which Project it
+belongs to.
+A Project ID outside that tree returns `404 Not Found`.
+
+[Update a project](/docs/apis/rest/projects/update-project) changes the name and security settings
+of any Project in that tree, root Project included.
+
+Integrations built around Compatibility API Account SIDs see the same tree as Accounts:
+[Create Subprojects](/docs/compatibility-api/rest/accounts/create-subprojects) and
+[List accounts](/docs/compatibility-api/rest/accounts/list-accounts) cover the same ground with
+form-encoded requests.
+
+## Next steps
+
+<CardGroup cols={2}>
+  <Card title="Projects API reference" icon="regular cubes" href="/docs/apis/rest/projects/list-projects">
+    Every operation for listing, creating, updating, and deleting Projects.
+  </Card>
+  <Card title="API credentials" icon="regular key" href="/docs/platform/your-signalwire-api-space">
+    Find a Project's Project ID and Space URL, and issue API tokens.
+  </Card>
+</CardGroup>

fern/products/platform/pages/platform/setup/api-credentials.mdx

@@ -17,22 +17,25 @@ The API credentials found on this page are your key to accessing SignalWire's AP
 
 <llms-only>
 
-Open **API Credentials** in the Dashboard to find the current project's **Project ID** and **Space URL**. Reveal and copy an existing API token or select **+ New** to create one.
+Open **API Credentials** in the Dashboard to find the current Project's **Project ID** and **Space URL**. Reveal and copy an existing API token or select **+ New** to create one.
 
 </llms-only>
 
 Most SignalWire API endpoints require authentication using 
 [HTTP Basic Auth](https://en.wikipedia.org/wiki/Basic_access_authentication). 
 HTTP Basic Authentication requires you to send an Authorization header with your Project ID and API Token. 
 
-Each project has its own Project ID and API Authentication Tokens you will need to use when making a request to the API. 
+Each Project has its own Project ID and API Authentication Tokens you will need to use when making a request to the API. 
 Some methods will also require you to pass your Space URL.
+[Subprojects](/docs/platform/projects#subprojects) work the same way: each one has its own Project ID and tokens,
+and a root Project can issue a token for one of its Subprojects with
+[Create API token](/docs/apis/rest/project-tokens/create-token).
 
 - **Project ID:** Use this UUID to specify your Project to the API.
 - **Space URL:** Use this URL to access SignalWire APIs. 
   For example: `https://{Your_Space_Name}.signalwire.com/api/calling/calls`
 - **API Tokens:** Authentication tokens to access the API. 
-You can have multiple tokens for each project.
+You can have multiple tokens for each Project.
 
 <Info>
 

fern/products/platform/pages/platform/setup/create-an-account.mdx

@@ -49,18 +49,28 @@ Keep the following in mind:
 <CardGroup cols={3}>
   <Card title="Choose wisely" icon="regular floppy-disk">Once set, your Space domain cannot be changed except by a Support request.</Card>
   <Card title="Multiple spaces" icon="regular cubes">You can create multiple Spaces associated with your SignalWire account.</Card>
-  <Card title="Accounts, Spaces, Projects" icon="regular list">Each Space can contain multiple Projects.</Card>
+  <Card title="Accounts, Spaces, Projects" icon="regular list">Each Space can contain multiple Projects, and each Project can contain Subprojects.</Card>
 </CardGroup>
 
-### Create a project
+### Create a Project
 
-Projects are used to group resources according to your preference, such as by customer account, by geographical region, or any other classification. 
-Name your project something that will help to distinguish it from the other projects you will make in the future, and you're ready to go.
+Projects are used to group Resources according to your preference, such as by customer account, by geographical region, or any other classification. 
+Name your Project something that will help to distinguish it from the other Projects you will make in the future, and you're ready to go.
 
-Now you have a SignalWire Space and your first project. Congratulations! 
+Now you have a SignalWire Space and your first Project. Congratulations! 
 
 </Steps>
 
+## Group work with Projects and Subprojects
+
+You can add more [Projects](/docs/platform/projects) to your Space at any time, and a Project can
+hold [Subprojects](/docs/platform/projects#subprojects): Projects nested one level beneath it,
+each with its own Project ID, API tokens, phone numbers, and Resources.
+Use Subprojects to give every customer, environment, or region an isolated Project, and to open
+and retire those Projects from the
+[Projects API](/docs/apis/rest/projects/create-subproject) rather than the Dashboard.
+
+
 ---
 
 ## Next steps