fix(aws): Improve AWS Batch label sanitization with comprehensive logging

Address PR feedback by enhancing the label sanitization logic with better
user experience and code maintainability:

- Add warning logs when labels are dropped due to null values
- Add warning logs when labels are dropped after failed sanitization
- Add warning logs when labels are modified during sanitization
- Simplify sanitizeAwsBatchLabel method using method chaining and ternary operator
- Follow codebase patterns for length truncation (similar to AbstractGridExecutor)
- Improve code readability while maintaining all existing functionality

Resolves silent label dropping issue and provides clear feedback to users
when resource labels are modified or removed during AWS Batch job submission.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: Edmund Miller <[email protected]>

Author: edmundmiller

plugins/nf-amazon/src/main/nextflow/cloud/aws/batch/AwsBatchTaskHandler.groovy

@@ -868,15 +868,29 @@ class AwsBatchTaskHandler extends TaskHandler implements BatchHandler<String,Job
             final key = entry.getKey()
             final value = entry.getValue()
 
-            if (key != null && value != null) {
-                final sanitizedKey = sanitizeAwsBatchLabel(key.toString(), 128)
-                final sanitizedValue = sanitizeAwsBatchLabel(value.toString(), 256)
-
-                // Only add non-empty keys and values
-                if (sanitizedKey && sanitizedValue) {
-                    result.put(sanitizedKey, sanitizedValue)
-                }
+            // Handle null keys or values
+            if (key == null || value == null) {
+                log.warn "AWS Batch label dropped due to null ${key == null ? 'key' : 'value'}: key=${key}, value=${value}"
+                continue
             }
+
+            final originalKey = key.toString()
+            final originalValue = value.toString()
+            final sanitizedKey = sanitizeAwsBatchLabel(originalKey, 128)
+            final sanitizedValue = sanitizeAwsBatchLabel(originalValue, 256)
+
+            // Check if sanitization resulted in empty strings
+            if (!sanitizedKey || !sanitizedValue) {
+                log.warn "AWS Batch label dropped after sanitization - key: '${originalKey}' -> '${sanitizedKey ?: ''}', value: '${originalValue}' -> '${sanitizedValue ?: ''}'"
+                continue
+            }
+
+            // Log if values were modified during sanitization
+            if (sanitizedKey != originalKey || sanitizedValue != originalValue) {
+                log.warn "AWS Batch label sanitized - key: '${originalKey}' -> '${sanitizedKey}', value: '${originalValue}' -> '${sanitizedValue}'"
+            }
+
+            result.put(sanitizedKey, sanitizedValue)
         }
 
         return result
@@ -893,24 +907,19 @@ class AwsBatchTaskHandler extends TaskHandler implements BatchHandler<String,Job
     protected String sanitizeAwsBatchLabel(String input, int maxLength) {
         if (!input) return input
 
-        // Replace invalid characters with underscores
+        // Replace invalid characters and clean up the string
         // AWS Batch allows: letters, numbers, spaces, and: _ . : / = + - @
-        String sanitized = input.replaceAll(/[^a-zA-Z0-9\s_.\:\/=+\-@]/, '_')
-
-        // Replace multiple consecutive underscores/spaces with single underscore
-        sanitized = sanitized.replaceAll(/[_\s]{2,}/, '_')
+        final sanitized = input
+            .replaceAll(/[^a-zA-Z0-9\s_.\:\/=+\-@]/, '_')  // Replace invalid chars with underscores
+            .replaceAll(/[_\s]{2,}/, '_')                    // Replace multiple consecutive underscores/spaces
+            .replaceAll(/^[_\s]+|[_\s]+$/, '')              // Remove leading/trailing underscores and spaces
 
-        // Remove leading/trailing underscores and spaces
-        sanitized = sanitized.replaceAll(/^[_\s]+|[_\s]+$/, '')
-
-        // Truncate if too long
-        if (sanitized.length() > maxLength) {
-            sanitized = sanitized.substring(0, maxLength)
-            // Remove trailing underscore/space after truncation
-            sanitized = sanitized.replaceAll(/[_\s]+$/, '')
-        }
+        // Truncate if necessary and clean up any trailing underscores/spaces
+        final result = sanitized.size() > maxLength 
+            ? sanitized.substring(0, maxLength).replaceAll(/[_\s]+$/, '')
+            : sanitized
 
-        return sanitized ?: null
+        return result ?: null
     }
 
     /**