Sentinel policies are checked after the plan stage of a Terraform run, but before it can be confirmed or the terraform apply is executed3. This allows you to enforce rules on your infrastructure before it is created or modified.

Terraform is built on a plugin-based architecture, enabling developers to extend Terraform by writing new plugins or compiling modified versions of existing plugins1. Terraform plugins are executable binaries written in Go that expose an implementation for a specific service, such as a cloud resource, SaaS platform, or API2. If there is no existing provider for your API, you can create one using the Terraform Plugin SDK3 or the Terraform Plugin Framework4. Reference =
* 1: Plugin Development - How Terraform Works With Plugins | Terraform | HashiCorp Developer
* 2: Lab: Terraform Plug-in Based Architecture - GitHub
* 3: Terraform Plugin SDK - Terraform by HashiCorp
* 4: HashiCorp Terraform Plugin Framework Now Generally Available

Changing the Terraform backend after performing the initialterraform applyis technically possible but strongly discouraged. This is because changing backends can lead to complexities in state management, requiring manual intervention such as state migration to ensure consistency. Terraform's documentation and best practices advise planning the backend configuration carefully before applying Terraform configurations to avoid such changes.References= This guidance is consistent with Terraform's official documentation, which recommends careful consideration and planning of backend configurations to avoid the need for changes.

If you manually destroy infrastructure, Terraform will automatically detect the change and update the state file during the next plan or apply. Terraform compares the current state of the infrastructure with the desired state in the configuration and generates a plan to reconcile the differences. If a resource is missing from the infrastructure but still exists in the state file, Terraform will attempt to recreate it. If a resource is present in the infrastructure but not in the state file, Terraform will ignore it unless you use the terraform import command to bring it under Terraform's management. Reference = [Terraform State]

Running terraform fmt without any flags in a directory with Terraform configuration files will not check the formatting of those files without changing their contents, but will actually rewrite them to a canonical format and style. If you want to check the formatting without making changes, you need to use the -check flag.