📝 Address PR feedback: Update custom markers documentation

- Remove Key Considerations section per reviewer feedback
- Update external plugin example to match current API pattern
- Fix external plugin integration code to use JSON/STDIN communication
- Simplify template example to be more realistic for external plugins
- Merge latest changes from master branch

Addresses feedback from PR review comments

Author: nerdeveloper

docs/book/src/plugins/extending/custom-markers.md

@@ -77,34 +77,23 @@ func formatPrefix(prefix string) string {
 }
 ```
 
-### Use in Template Files
+### Use in Template Generation
 
 ```go
 package templates
 
 import (
     "fmt"
-    "path/filepath"
-    "sigs.k8s.io/kubebuilder/v4/pkg/machinery"
     "github.com/yourorg/yourplugin/pkg/markers"
 )
 
-type RustMainFile struct {
-    machinery.TemplateMixin
-    machinery.ProjectNameMixin
-}
-
-func (f *RustMainFile) SetTemplateDefaults() error {
-    if f.Path == "" {
-        f.Path = filepath.Join("src", "main.rs")
-    }
-
-    marker, err := markers.NewRustMarker(f.Path, "imports")
+func GenerateRustFile(projectName string) (string, error) {
+    marker, err := markers.NewRustMarker("src/main.rs", "imports")
     if err != nil {
-        return err
+        return "", err
     }
 
-    f.TemplateBody = fmt.Sprintf(`// Generated by Rust Plugin
+    content := fmt.Sprintf(`// Generated by Rust Plugin
 %s
 
 use std::error::Error;
@@ -113,9 +102,19 @@ fn main() -> Result<(), Box<dyn Error>> {
     println!("Hello from %s!");
     Ok(())
 }
-`, marker.String(), f.ProjectName)
+`, marker.String(), projectName)
 
-    return nil
+    return content, nil
+}
+
+func GenerateCargoToml(projectName string) string {
+    return fmt.Sprintf(`[package]
+name = "%s"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+`, projectName)
 }
 ```
 
@@ -125,27 +124,86 @@ fn main() -> Result<(), Box<dyn Error>> {
 package main
 
 import (
-    "sigs.k8s.io/kubebuilder/v4/pkg/plugin"
+    "bufio"
+    "encoding/json"
+    "fmt"
+    "io"
+    "os"
+    "path/filepath"
+    
     "sigs.k8s.io/kubebuilder/v4/pkg/plugin/external"
-    "github.com/yourorg/yourplugin/pkg/templates"
+    "github.com/yourorg/yourplugin/pkg/markers"
 )
 
 func main() {
-    p := &external.Plugin{
-        Name:    "rust.kubebuilder.io",
-        Version: plugin.Version{Number: 1, Stage: plugin.Alpha},
-
-        Init: func(req external.PluginRequest) external.PluginResponse {
-            mainFile := &templates.RustMainFile{}
-
-            return external.PluginResponse{
-                Universe: req.Universe,
-                Files: []machinery.File{mainFile},
-            }
-        },
+    // External plugins communicate via JSON over STDIN/STDOUT
+    reader := bufio.NewReader(os.Stdin)
+    input, err := io.ReadAll(reader)
+    if err != nil {
+        returnError(fmt.Errorf("error reading STDIN: %w", err))
+        return
     }
 
-    external.Run(p)
+    pluginRequest := &external.PluginRequest{}
+    err = json.Unmarshal(input, pluginRequest)
+    if err != nil {
+        returnError(fmt.Errorf("error unmarshaling request: %w", err))
+        return
+    }
+
+    var response external.PluginResponse
+
+    switch pluginRequest.Command {
+    case "init":
+        response = handleInit(pluginRequest)
+    case "flags":
+        response = handleFlags(pluginRequest)
+    case "metadata":
+        response = handleMetadata(pluginRequest)
+    default:
+        response = external.PluginResponse{
+            Command: pluginRequest.Command,
+            Error:   true,
+            ErrorMsgs: []string{fmt.Sprintf("unknown command: %s", pluginRequest.Command)},
+        }
+    }
+
+    output, _ := json.Marshal(response)
+    fmt.Printf("%s", output)
+}
+
+func handleInit(req *external.PluginRequest) external.PluginResponse {
+    // Create Rust file with custom markers
+    marker, _ := markers.NewRustMarker("src/main.rs", "imports")
+    
+    fileContent := fmt.Sprintf(`// Generated by Rust Plugin
+%s
+
+use std::error::Error;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    println!("Hello from Rust!");
+    Ok(())
+}
+`, marker.String())
+
+    // External plugins use "universe" to represent file changes
+    universe := make(map[string]string)
+    universe["src/main.rs"] = fileContent
+    
+    return external.PluginResponse{
+        Command:  "init",
+        Universe: universe,
+    }
+}
+
+func returnError(err error) {
+    response := external.PluginResponse{
+        Error:     true,
+        ErrorMsgs: []string{err.Error()},
+    }
+    output, _ := json.Marshal(response)
+    fmt.Printf("%s", output)
 }
 ```
 
@@ -157,14 +215,4 @@ To support other file extensions, modify the marker implementation by changing:
 - The file extension check (e.g., `.java`, `.py`, `.tpl`)
 - The marker prefix (e.g., `+java:scaffold:`, `+python:scaffold:`)
 
-## Key Considerations
-
-1. **Unique Prefixes**: Choose a unique prefix for your plugin to avoid conflicts (e.g., `+rust:scaffold:`, `+java:scaffold:`)
-
-2. **Comment Syntax**: Different languages have different comment syntax. Ensure you map the correct comment style for each file extension
-
-3. **Error Handling**: Validate file extensions and return clear error messages for unsupported files
-
-4. **Testing**: Test your marker implementation with various scenarios to ensure reliability
-
 For more information on creating external plugins, see [External Plugins](external-plugins.md).