fix: use proper JSON marshaling for customrest prompt to handle special characters (#1615)

This fixes issue #1556 where the customrest backend fails when error messages
contain quotes or other special characters.

The root cause was that fmt.Sprintf was used to construct JSON, which doesn't
escape special characters like quotes, newlines, or tabs. When Kubernetes error
messages contain image names with quotes (e.g., "nginx:1.a.b.c"), the resulting
JSON was malformed and failed to parse.

The fix uses json.Marshal to properly construct the JSON payload, which
automatically handles all special character escaping according to JSON spec.

Fixes #1556

Signed-off-by: Three Foxes (in a Trenchcoat) <threefoxes53235@gmail.com>
Co-authored-by: Three Foxes (in a Trenchcoat) <threefoxes53235@gmail.com>

Author: three-foxes-in-a-trenchcoat

pkg/analysis/analysis.go

@@ -16,6 +16,7 @@ package analysis
 import (
 	"context"
 	"encoding/base64"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"reflect"
@@ -526,7 +527,22 @@ func (a *Analysis) getAIResultForSanitizedFailures(texts []string, promptTmpl st
 	// Process template.
 	prompt := fmt.Sprintf(strings.TrimSpace(promptTmpl), a.Language, inputKey)
 	if a.AIClient.GetName() == ai.CustomRestClientName {
-		prompt = fmt.Sprintf(ai.PromptMap["raw"], a.Language, inputKey, prompt)
+		// Use proper JSON marshaling to handle special characters in error messages
+		// This fixes issues with quotes, newlines, and other special chars in inputKey
+		customRestPrompt := struct {
+			Language string `json:"language"`
+			Message  string `json:"message"`
+			Prompt   string `json:"prompt"`
+		}{
+			Language: a.Language,
+			Message:  inputKey,
+			Prompt:   prompt,
+		}
+		promptBytes, err := json.Marshal(customRestPrompt)
+		if err != nil {
+			return "", fmt.Errorf("failed to marshal customrest prompt: %w", err)
+		}
+		prompt = string(promptBytes)
 	}
 	response, err := a.AIClient.GetCompletion(a.Context, prompt)
 	if err != nil {