Add default value and validation to agent_name variable

Ensure that agent_name defaults to an empty string, and introduce
validation to require it when subdomain is true. This aligns with
expected behavior and prevents misconfiguration.

filebrowser/README.md

@@ -13,10 +13,9 @@ A file browser for your workspace.
 
 ```tf
 module "filebrowser" {
-  source     = "registry.coder.com/modules/filebrowser/coder"
-  version    = "1.0.18"
-  agent_id   = coder_agent.example.id
-  agent_name = "main"
+  source   = "registry.coder.com/modules/filebrowser/coder"
+  version  = "1.0.18"
+  agent_id = coder_agent.example.id
 }
 ```
 
@@ -28,11 +27,10 @@ module "filebrowser" {
 
 ```tf
 module "filebrowser" {
-  source     = "registry.coder.com/modules/filebrowser/coder"
-  version    = "1.0.18"
-  agent_id   = coder_agent.example.id
-  agent_name = "main"
-  folder     = "/home/coder/project"
+  source   = "registry.coder.com/modules/filebrowser/coder"
+  version  = "1.0.18"
+  agent_id = coder_agent.example.id
+  folder   = "/home/coder/project"
 }
 ```
 
@@ -43,7 +41,6 @@ module "filebrowser" {
   source        = "registry.coder.com/modules/filebrowser/coder"
   version       = "1.0.18"
   agent_id      = coder_agent.example.id
-  agent_name    = "main"
   database_path = ".config/filebrowser.db"
 }
 ```

filebrowser/main.tf

@@ -21,6 +21,12 @@ data "coder_workspace_owner" "me" {}
 variable "agent_name" {
   type        = string
   description = "The name of the main deployment. (Used to build the subpath for coder_app.)"
+  default     = ""
+  validation {
+    # If subdomain is true, then agent_name must be set.
+    condition     = var.subdomain ? var.agent_name != "" : true
+    error_message = "The agent_name must be set."
+  }
 }
 
 variable "database_path" {