heroku
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diff --git a/‎docs/data-sources/app.md‎
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diff --git a/‎docs/resources/app.md‎
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@@ -2,7 +2,8 @@ name: Acceptance
 on:
   pull_request:
     branches:
-    - master
+      - master
+      - fir-compatibility
     paths-ignore:
       - 'docs/**'
       - '**.md'
 
@@ -32,3 +32,5 @@ website/vendor
 # Test exclusions
 !command/test-fixtures/**/*.tfstate
 !command/test-fixtures/**/.terraform/
+
+.cursor/
@@ -0,0 +1,2 @@
+golang 1.24.5
+terraform 1.5.7
@@ -8,7 +8,9 @@ description: |-
 
 # Data Source: heroku_app
 
-Use this data source to get information about a Heroku App.
+Use this data source to get information about a Heroku app.
+
+~> **NOTE:** This resource is only supported for apps that use [classic buildpacks](https://devcenter.heroku.com/articles/buildpacks#classic-buildpacks).
 
 ## Example Usage
 
@@ -23,50 +25,48 @@ data "heroku_app" "default" {
 
 The following arguments are supported:
 
-* `name` - (Required) The name of the application. In Heroku, this is also the
+* `name`: (Required) The name of the application. In Heroku, it's a
    unique ID, so it must be unique and have a minimum of 3 characters.
 
 ## Attributes Reference
 
 The following attributes are exported:
 
-* `id` - The unique UUID of the Heroku app.
+* `id`: The unique UUID of the Heroku app.
 
-* `name` - The name of the application. In Heroku, this is also the
+* `name`: The name of the application. In Heroku, it's also the
    unique ID.
 
-* `stack` - The application stack is what platform to run the application
-   in.
+* `stack`: The application [stack](https://devcenter.heroku.com/articles/stack) is what platform to run the application in.
 
-* `buildpacks` - A list of buildpacks that this app uses.
+* `buildpacks`: A list of buildpacks that this app uses.
 
-* `space` - The private space in which the app runs. Not present if this is a common runtime app.
+* `space`: The [space](https://devcenter.heroku.com/articles/private-spaces) in which the app runs. Not present for [Common Runtime](https://devcenter.heroku.com/articles/dyno-runtime#common-runtime) apps.
 
-* `region` - The region in which the app is deployed.
+* `region`: The region in the app is deployed in.
 
-* `git_url` - The Git URL for the application. This is used for
+* `git_url`: The Git URL for the application, used for
    deploying new versions of the app.
 
-* `web_url` - The web (HTTP) URL that the application can be accessed
-   at by default.
+* `web_url`: The web (HTTP) URL to access the application at by default.
 
-* `heroku_hostname` - The hostname for the Heroku application, suitable
+* `heroku_hostname`: The hostname for the Heroku application, suitable
    for pointing DNS records.
 
-* `last_release_id` - The last successful Release ID for the app. May be empty.
+* `last_release_id`: The last successful Release ID for the app. May be empty.
 
-* `last_slug_id` - The Slug ID from the last successful release. May be empty.
+* `last_slug_id`: The slug ID from the last successful release. May be empty.
 
-* `config_vars` - A map of all configuration variables for the app.
+* `config_vars`: The map of all configuration variables for the app.
 
-* `acm` - True if Heroku ACM is enabled for this app, false otherwise.
+* `acm`: True if [Heroku Automated Certificate Management](https://devcenter.heroku.com/articles/automated-certificate-management) is enabled for this app, false otherwise.
 
-* `organization` - The Heroku Team that owns this app. 
+* `organization`: The Heroku team that owns this app. 
 
-  * `name` - The name of the Heroku Team (organization).
+  * `name`: The name of the Heroku team (organization).
 
-  * `locked` - True if the app access is locked
+  * `locked`: True if the app access is locked
 
-  * `personal`
+  * `personal`: True for personal apps
 
-* `uuid` - The unique UUID of the Heroku app.
+* `uuid`: The unique UUID of the Heroku app.
@@ -3,21 +3,25 @@ layout: "heroku"
 page_title: "Heroku: heroku_app"
 sidebar_current: "docs-heroku-resource-app-x"
 description: |-
-  Provides a Heroku App resource. This can be used to create and manage applications on Heroku.
+  Provides a Heroku App resource. Use this resource to create and manage applications on Heroku.
 ---
 
 # heroku\_app
 
-Provides a Heroku App resource. This can be used to create and manage applications on Heroku.
+Provides a [Heroku App](https://devcenter.heroku.com/articles/platform-api-reference#app) resource. Use this resource to create and manage applications on Heroku.
 
--> **Always reference apps by ID (UUID) in Terraform configuration**
-Starting with v5.0 of this provider, all HCL app references are by ID. Read more details in [Upgrading](guides/upgrading.html).
+The Heroku platform supports two [generations](https://devcenter.heroku.com/articles/generations):
+- **Cedar** (default): Legacy platform with support for classic buildpacks, stack configuration, and internal routing
+- **Fir**: Next-generation platform with enhanced security, and modern containerization
+
+-> **Note:** Always reference apps by ID (UUID) in Terraform configuration. Starting with v5.0 of this provider, all HCL app references are by ID. Read more details in [Upgrading](guides/upgrading.html).
 
 ## Example Usage
 
+### Cedar Generation Using Classic Buildpacks (Default)
 ```hcl-terraform
-resource "heroku_app" "default" {
-  name   = "my-cool-app"
+resource "heroku_app" "cedar_app" {
+  name   = "my-cedar-app"
   region = "us"
 
   config_vars = {
@@ -27,12 +31,43 @@ resource "heroku_app" "default" {
   buildpacks = [
     "heroku/go"
   ]
+  
+  stack = "heroku-22"
+}
+```
+
+### Fir Generation Using Cloud Native Buildpacks (via Fir Space)
+```hcl-terraform
+# Create a Fir-generation space first
+resource "heroku_space" "fir_space" {
+  name         = "my-fir-space"
+  organization = "my-org"
+  region       = "virginia"
+  generation   = "fir"
+}
+
+# Apps deployed to Fir spaces automatically use Fir generation
+resource "heroku_app" "fir_app" {
+  name   = "my-fir-app"
+  region = "virginia"
+  space  = heroku_space.fir_space.name
+
+  organization {
+    name = "my-org"
+  }
+
+  config_vars = {
+    FOOBAR = "baz"
+  }
+  
+  # Note: buildpacks and stack are not supported for Fir-generation apps as they use Cloud Native Buildpacks
+  # Use project.toml in your application code instead
 }
 ```
 
 ## Example Usage for a Team
 
-A Heroku "team" was originally called an "organization", and that is still the identifier used in this resource.
+A Heroku "team" was originally called an "organization", and that's still the identifier used in this resource.
 
 ```hcl-terraform
 resource "heroku_app" "default" {
@@ -47,80 +82,147 @@ resource "heroku_app" "default" {
 
 ## Argument Reference
 
-The following arguments are supported:
-
-* `name` - (Required) The name of the application. In Heroku, this is also the
-   unique ID, so it must be unique and have a minimum of 3 characters.
-* `region` - (Required) The region that the app should be deployed in.
-* `stack` - (Optional) The application stack is what platform to run the application in.
-* `buildpacks` - (Optional) Buildpack names or URLs for the application.
-  Buildpacks configured externally won't be altered if this is not present.
-* `config_vars`<sup>[1](#deleting-vars)</sup> - (Optional) Configuration variables for the application.
-     The config variables in this map are not the final set of configuration
-     variables, but rather variables you want present. That is, other
-     configuration variables set externally won't be removed by Terraform
+The resource supports the following arguments:
+
+* `name`: (Required) The name of the application. In Heroku, this argument is the unique ID, so it must be unique and have a minimum of 3 characters.
+* `region`: (Required) The region to deploy the app in.
+* `generation`: (Computed) Generation of the app platform. Automatically determined based on the space the app is deployed to. Apps in Fir-generation spaces are `fir`, all other apps are `cedar`.
+   - `cedar`: Legacy platform supporting classic buildpacks, stack configuration, and internal routing.
+   - `fir`: Next-generation platform with Cloud Native Buildpacks (CNB). No support for `buildpacks`, `stack`, or `internal_routing` fields.
+* `stack`: (Optional) The name of the [stack](https://devcenter.heroku.com/articles/stack) to run the application in. **Note**: Not supported for `fir` generation apps.
+* `buildpacks`: (Optional) Classic buildpack names or URLs for the application.
+  Buildpacks configured externally won't be altered if this isn't present. **Note**: Not supported for apps using Cloud Native Buildpacks, like Fir-generation apps. Use `project.toml` for configuration instead.
+* `config_vars`<sup>[1](#deleting-vars)</sup>: (Optional) Configuration variables for the application.
+     The config variables in this map aren't the final set of configuration
+     variables, but rather variables you want present. Terraform doesn't remove configuration variables set externally
      if they aren't present in this list.
-* `sensitive_config_vars`<sup>[1](#deleting-vars)</sup> - (Optional) This argument is the same as `config_vars`.
+* `sensitive_config_vars`<sup>[1](#deleting-vars)</sup>: (Optional) This argument is the same as `config_vars`.
      The main difference between the two is when `sensitive_config_vars` outputs
-     are displayed on-screen following a terraform apply or terraform refresh,
-     they are redacted, with <sensitive> displayed in place of their value.
-     It is recommended to put private keys, passwords, etc in this argument.
-* `space` - (Optional) The name of a private space to create the app in.
-* `internal_routing` - (Optional) If true, the application will be routable
-  only internally in a private space. This option is only available for apps
-  that also specify `space`.
-* `organization` - (Optional) A block that can be specified once to define
+     are displayed on-screen following a `terraform apply` or `terraform refresh`,
+     they're redacted, with `<sensitive>` displayed in place of their value.
+     It's recommended to put sensitive information like private keys, and passwords in this argument.
+* `space`: (Optional) The name of the space to create the app in.
+* `internal_routing` - (Optional) If true, the application is routable
+  only internally in Heroku Private Spaces. This option is only available for apps
+  that also specify `space`. **Note**: Only supported for apps in Cedar-generation spaces.
+* `organization`: (Optional) Specify this block once to define
      Heroku Team settings for this app. The fields for this block are
      documented below.
-* `acm` - (Optional) The flag representing Automated Certificate Management for the app.
+* `acm`: (Optional) If Automated Certificate Management is enabled for the app.
 
 The `organization` block supports:
-* `name` (string) - The name of the Heroku Team.
-* `locked` (boolean) - Are other team members forbidden from joining this app.
-* `personal` (boolean) - Force creation of the app in the user account even if a default team is set.
+* `name` (string): The name of the Heroku Team.
+* `locked` (boolean): If other team members are forbidden from joining this app.
+* `personal` (boolean): Force creation of the app in the user's account, even if a default team is set.
 
-### Deleting vars
+### Deleting Vars
 
 Deleting an entire `config_vars` or `sensitive_config_vars` map from a `heroku_app`
-configuration will not actually remove the vars on the remote resource. To remove an existing variable,
-leave these attribute maps in-place and delete only its entries from the map. Once these attributes are
-empty, the map itself may be deleted from the configuration. Otherwise if one deletes the map with existing
-entries, the config vars will not be deleted from the remote resource.
+configuration doesn't remove the variables on the remote resource. To remove an existing variable,
+leave these attribute maps in-place and only delete its entries from the map. After these attributes are
+empty, you can delete the map itself from the configuration. Otherwise, if you delete the map with existing
+entries, the config vars don't get deleted from the remote resource.
 
-This is especially important if you are migrating all `config_vars` to `sensitive_config_vars` or migrating
-config vars to `heroku_app_config_association` resource.
+If you're migrating all `config_vars` to `sensitive_config_vars`, or migrating
+config vars to `heroku_app_config_association` resource, this behavior is especially important.
 
 ## Attributes Reference
 
 The following attributes are exported:
 
-* `id` - The ID (UUID) of the app.
-* `name` - The name of the app.
-* `stack` - The application stack is what platform to run the application in.
-* `space` - The private space the app should run in.
-* `internal_routing` - Whether internal routing is enabled the private space app.
-* `region` - The region that the app should be deployed in.
-* `git_url` - The Git URL for the application. This is used for
+* `id`: The ID (UUID) of the app.
+* `name`: The name of the app.
+* `generation`: Generation of the app platform (`cedar` or `fir`). Automatically determined from the space the app is deployed to.
+* `stack`: The name of the [stack](https://devcenter.heroku.com/articles/stack) the application is run in.
+* `space`: The space the app is in.
+* `internal_routing`: If internal routing is enabled. Only for apps in Heroku Private Spaces.
+* `region`: The region that the app is deployed to.
+* `git_url`: The Git URL for the application, used for
    deploying new versions of the app.
-* `web_url` - The web (HTTP) URL that the application can be accessed
-   at by default.
-* `heroku_hostname` - A hostname for the Heroku application, suitable
+* `web_url`: The web (HTTP) URL for accessing the application by default.
+* `heroku_hostname`: The hostname for the Heroku application, suitable
    for pointing DNS records.
-* `all_config_vars` - A map of all configuration variables that
+* `all_config_vars`: The map of all configuration variables that
   exist for the app, containing both those set by Terraform and those
-  set externally. (These are treated as "sensitive" so that
-  their values are redacted in console output.) This attribute is not set in state if the `provider`
+  set externally. These variables are treated as "sensitive" so that
+  their values are redacted in console output. This attribute isn't set in state if the `provider`
   attribute `set_app_all_config_vars_in_state` is `false`.
-* `uuid` - The unique UUID of the Heroku app. **NOTE:** Use this for `null_resource` triggers.
+* `uuid`: The unique UUID of the Heroku app. **Note:** Use this attribute for `null_resource` triggers.
+
+## Cloud Native Buildpacks
+
+When apps are deployed to Fir-generation spaces, they automatically use Cloud Native Buildpacks (CNB) instead of classic Heroku buildpacks. CNBs require different configuration approaches:
+
+### project.toml Configuration
+
+Instead of specifying `buildpacks` in Terraform, create a `project.toml` file in your application root:
+
+```toml
+[build]
+[[build.buildpacks]]
+id = "heroku/nodejs"
+
+[[build.buildpacks]] 
+id = "heroku/procfile"
+
+[build.env]
+BP_NODE_VERSION = "18.*"
+```
+
+### Migration from Cedar to Fir
+
+When migrating from Cedar to Fir generation:
+
+1. **Create a Fir space**: Create a new space with `generation = "fir"`.
+2. **Remove unsupported fields**: Remove `buildpacks`, `stack`, and `internal_routing` from your Terraform configuration.
+3. **Add a `project.toml` file**: Create a `project.toml` file in your application code with Cloud Native Buildpacks configuration.
+4. **Update the `space`**: Change your app's `space` to use the Fir space.
+5. **Redeploy**: Deploy your application with the new configuration.
+
+```hcl-terraform
+# Before (Cedar)
+resource "heroku_space" "cedar_space" {
+  name         = "my-space"
+  organization = "my-org"
+  region       = "virginia"
+}
+
+resource "heroku_app" "example" {
+  name   = "my-app"
+  region = "virginia"
+  space  = heroku_space.cedar_space.name
+  
+  buildpacks = ["heroku/nodejs"]
+  stack      = "heroku-22"
+}
+
+# After (Fir)
+resource "heroku_space" "fir_space" {
+  name         = "my-space-fir"
+  organization = "my-org"
+  region       = "virginia" 
+  generation   = "fir"
+}
+
+resource "heroku_app" "example" {
+  name   = "my-app"
+  region = "virginia"
+  space  = heroku_space.fir_space.name
+  
+  # buildpacks and stack removed - configured via project.toml
+  # generation is automatically "fir" from the space
+}
+```
 
 ## Import
 
-Apps can be imported using an existing app's `UUID` or name.
+Import apps with an existing app's `UUID` or name.
 
 For example:
 ```
 $ terraform import heroku_app.foobar MyApp
 $ terraform import heroku_app.foobar e74ac056-7d00-4a7e-aa80-df4bc413a825
 ```
 
-Please note: `config_vars` & `sensitive_config_vars` will not be imported due to limitations of Terraform's import process (see [issue](https://github.com/heroku/terraform-provider-heroku/issues/247#issuecomment-602013774)). All vars will appear to be added on the next plan/apply. The diff may be manually reconciled using the outputs of `heroku config` & `terraform plan`.
+>[!NOTE]
+>`config_vars` & `sensitive_config_vars` aren't imported due to limitations of Terraform's import process (see [issue](https://github.com/heroku/terraform-provider-heroku/issues/247#issuecomment-602013774)). All vars appear to be added on the next plan/apply. Manually reconcile the diff using the outputs of `heroku config` & `terraform plan`.