feat(cli): prompt for missing required template variables on template creation (#19973)

## Summary

In this pull request we're adding support in the CLI for prompting the
user for any missing required template variables in the `coder templates
push` command and automatically retrying the template build once a user
has provided any missing variable values.

Closes: https://github.com/coder/coder/issues/19782

### Demo

In the following recording I created a simple template terraform file
that used different variable types (string, number, boolean, and
sensitive) and prompted the user to enter a value for each variable.

<details>
<summary>See example template terraform file</summary>

```tf
...

# Required variables for testing interactive prompting
variable "docker_image" {
  description = "Docker image to use for the workspace"
  type        = string
}

variable "workspace_name" {
  description = "Name of the workspace"
  type        = string
}

variable "cpu_limit" {
  description = "CPU limit for the container (number of cores)"
  type        = number
}

variable "enable_gpu" {
  description = "Enable GPU access for the container"
  type        = bool
}

variable "api_key" {
  description = "API key for external services (sensitive)"
  type        = string
  sensitive   = true
}

# Optional variable with default
variable "docker_socket" {
  default     = "/var/run/docker.sock"
  description = "Docker socket path"
  type        = string
}

...
```

</details>

Once the user entered a valid value for each variable, the template
build would be retried.


https://github.com/user-attachments/assets/770cf954-3cbc-4464-925e-2be4e32a97de

<details>
<summary>See output from recording</summary>

```shell
$ ./scripts/coder-dev.sh templates push test-required-params -d examples/templates/test-required-params/
INFO : Overriding codersdk.SessionTokenCookie as we are developing inside a Coder workspace.
/home/coder/coder/build/coder-slim_2.26.0-devel+a68122ca3_linux_amd64
Provisioner tags:  <none>
WARN: No .terraform.lock.hcl file found
  | When provisioning, Coder will be unable to cache providers without a lockfile and must download them from the internet each time.
  | Create one by running  terraform init  in your template directory.
> Upload "examples/templates/test-required-params"? (yes/no) yes
=== ✔ Queued [0ms]
==> ⧗ Running
==> ⧗ Running
=== ✔ Running [4ms]
==> ⧗ Setting up
=== ✔ Setting up [0ms]
==> ⧗ Parsing template parameters
=== ✔ Parsing template parameters [8ms]
==> ⧗ Cleaning Up
=== ✘ Cleaning Up [4ms]
=== ✘ Cleaning Up [8ms]
Found 5 missing required variables:
  - docker_image (string): Docker image to use for the workspace
  - workspace_name (string): Name of the workspace
  - cpu_limit (number): CPU limit for the container (number of cores)
  - enable_gpu (bool): Enable GPU access for the container
  - api_key (string): API key for external services (sensitive)

The template requires values for the following variables:
var.docker_image (required)
  Description: Docker image to use for the workspace
  Type: string
  Current value: <empty>
> Enter value: image-name
var.workspace_name (required)
  Description: Name of the workspace
  Type: string
  Current value: <empty>
> Enter value: workspace-name
var.cpu_limit (required)
  Description: CPU limit for the container (number of cores)
  Type: number
  Current value: <empty>
> Enter value: 1
var.enable_gpu (required)
  Description: Enable GPU access for the container
  Type: bool
  Current value: <empty>
? Select value: false
var.api_key (required), sensitive
  Description: API key for external services (sensitive)
  Type: string
  Current value: <empty>
> Enter value: (*redacted*) ******

Retrying template build with provided variables...
=== ✔ Queued [0ms]
==> ⧗ Running
==> ⧗ Running
=== ✔ Running [2ms]
==> ⧗ Setting up
=== ✔ Setting up [0ms]
==> ⧗ Parsing template parameters
=== ✔ Parsing template parameters [7ms]
==> ⧗ Detecting persistent resources
2025-09-25 22:34:14.731Z Terraform 1.13.0
2025-09-25 22:34:15.140Z data.coder_provisioner.me: Refreshing...
2025-09-25 22:34:15.140Z data.coder_workspace.me: Refreshing...
2025-09-25 22:34:15.140Z data.coder_workspace_owner.me: Refreshing...
2025-09-25 22:34:15.141Z data.coder_provisioner.me: Refresh complete after 0s [id=2bd73098-d127-4362-b3a5-628e5bce6998]
2025-09-25 22:34:15.141Z data.coder_workspace_owner.me: Refresh complete after 0s [id=c2006933-4f3e-4c45-9e04-79612c3a5eca]
2025-09-25 22:34:15.141Z data.coder_workspace.me: Refresh complete after 0s [id=36f2dc6f-0bf2-43bd-bc4d-b29768334e02]
2025-09-25 22:34:15.186Z coder_agent.main: Plan to create
2025-09-25 22:34:15.186Z module.code-server[0].coder_app.code-server: Plan to create
2025-09-25 22:34:15.186Z docker_volume.home_volume: Plan to create
2025-09-25 22:34:15.186Z module.code-server[0].coder_script.code-server: Plan to create
2025-09-25 22:34:15.187Z docker_container.workspace[0]: Plan to create
2025-09-25 22:34:15.187Z Plan: 5 to add, 0 to change, 0 to destroy.
=== ✔ Detecting persistent resources [3104ms]
==> ⧗ Detecting ephemeral resources
2025-09-25 22:34:16.033Z Terraform 1.13.0
2025-09-25 22:34:16.428Z data.coder_workspace.me: Refreshing...
2025-09-25 22:34:16.428Z data.coder_provisioner.me: Refreshing...
2025-09-25 22:34:16.429Z data.coder_workspace_owner.me: Refreshing...
2025-09-25 22:34:16.429Z data.coder_provisioner.me: Refresh complete after 0s [id=2d2f7083-88e6-425c-9df3-856a3bf4cc73]
2025-09-25 22:34:16.429Z data.coder_workspace.me: Refresh complete after 0s [id=c723575e-c7d3-43d7-bf54-0e34d0959dc3]
2025-09-25 22:34:16.431Z data.coder_workspace_owner.me: Refresh complete after 0s [id=d43470c2-236e-4ae9-a977-6b53688c2cb1]
2025-09-25 22:34:16.453Z coder_agent.main: Plan to create
2025-09-25 22:34:16.453Z docker_volume.home_volume: Plan to create
2025-09-25 22:34:16.454Z Plan: 2 to add, 0 to change, 0 to destroy.
=== ✔ Detecting ephemeral resources [1278ms]
==> ⧗ Cleaning Up
=== ✔ Cleaning Up [6ms]
┌──────────────────────────────────┐
│ Template Preview                 │
├──────────────────────────────────┤
│ RESOURCE                         │
├──────────────────────────────────┤
│ docker_container.workspace       │
│ └─ main (linux, amd64)           │
├──────────────────────────────────┤
│ docker_volume.home_volume        │
└──────────────────────────────────┘

The test-required-params template has been created at Sep 25
22:34:16! Developers can provision a workspace with this template using:

Updated version at Sep 25 22:34:16!
```

</details>

### Changes

- Added a new function to check if the provisioner failed due to a
template missing required variables
- Added a handler function that is called when a provisioner fails due
to the "missing required variables" error. The handler function will:
- Check for provided template variables and identify any missing
variables
- Prompt the user for any missing variables (prompt is adapted based on
the variable type)
  - Validate user input for missing variables
- Retry the template build when all variables have been provided by the
user

### Testing

Added tests for the following scenarios:

- Ensure validation based on variable type
- Ensure users are not prompted for variables with a default value
- Ensure variables provided via a variables files (`--variables-file`)
or a variable flag (`--variable`) take precedence over a template

codersdk/provisionerdaemons.go

@@ -175,6 +175,12 @@ func JobIsMissingParameterErrorCode(code JobErrorCode) bool {
 	return string(code) == runner.MissingParameterErrorCode
 }
 
+// JobIsMissingRequiredTemplateVariableErrorCode returns whether the error is a missing a required template
+// variable error. This can indicate to consumers that they need to provide required template variables.
+func JobIsMissingRequiredTemplateVariableErrorCode(code JobErrorCode) bool {
+	return string(code) == runner.RequiredTemplateVariablesErrorCode
+}
+
 // ProvisionerJob describes the job executed by the provisioning daemon.
 type ProvisionerJob struct {
 	ID               uuid.UUID              `json:"id" format:"uuid" table:"id"`

codersdk/templatevariables.go

@@ -68,7 +68,7 @@ func ParseUserVariableValues(varsFiles []string, variablesFile string, commandLi
 		return nil, err
 	}
 
-	return combineVariableValues(fromVars, fromFile, fromCommandLine), nil
+	return CombineVariableValues(fromVars, fromFile, fromCommandLine), nil
 }
 
 func parseVariableValuesFromVarsFiles(varsFiles []string) ([]VariableValue, error) {
@@ -252,7 +252,7 @@ func parseVariableValuesFromCommandLine(variables []string) ([]VariableValue, er
 	return values, nil
 }
 
-func combineVariableValues(valuesSets ...[]VariableValue) []VariableValue {
+func CombineVariableValues(valuesSets ...[]VariableValue) []VariableValue {
 	combinedValues := make(map[string]string)
 
 	for _, values := range valuesSets {