CRITICAL FIX: Overhaul PHP-FPM recommendation algorithm for shared hosting safety

- Fix: Memory-based calculator now accounts for MySQL memory usage
- Fix: Changed safety buffer from 15% to 50% (much more conservative)
- Fix: Hard cap recommendations at 150 max_children per domain on shared hosting
- Fix: Added combined capacity validation to prevent OOM scenarios
- Fix: Use realistic 20MB per process default instead of 1MB
- Fix: Added critical warning when server has <20% RAM headroom
- Feature: Step 2b now validates that combined domain recommendations fit in RAM
- Feature: Automatically scales down recommendations if they exceed 60% of total RAM
- Safety: Previous recommendations of 227 for 8GB server would now be capped at 150

This prevents dangerous situations like:
  - Domain with 421 requests getting 227 max_children (would need ~28GB)
  - Combined pools exceeding available RAM
  - OOM crashes from over-provisioned settings

Tested on 8GB server with 2 domains: Now recommends 105 + 31 instead of 227 + 31

lib/php-calculator-improved.sh

@@ -105,30 +105,47 @@ calculate_max_children_memory_based() {
     local reserved_mb
     reserved_mb=$(get_field "$reserve_result" 1)
 
-    # Available memory for PHP-FPM
-    local available_mb=$((total_ram_mb - reserved_mb))
+    # Account for MySQL memory (critical on shared hosting!)
+    local mysql_memory_mb=0
+    local mysql_info
+    mysql_info=$(detect_mysql_memory_usage 2>/dev/null)
+    if [ $? -eq 0 ]; then
+        mysql_memory_mb=$(echo "$mysql_info" | cut -d'|' -f3)
+    fi
+
+    # Available memory for PHP-FPM (after system + MySQL reserves)
+    # CRITICAL: This is shared across ALL domains, not per-domain!
+    local available_mb=$((total_ram_mb - reserved_mb - mysql_memory_mb))
+
+    # Safety check: never allow PHP-FPM to use more than 60% of RAM
+    local max_php_fpm=$((total_ram_mb * 60 / 100))
+    if [ "$available_mb" -gt "$max_php_fpm" ]; then
+        available_mb=$max_php_fpm
+    fi
 
     # Convert average KB to MB
     local avg_mb=$((avg_kb / 1024))
     if [ "$avg_mb" -eq 0 ]; then
-        avg_mb=1  # Minimum 1MB to prevent division issues
+        avg_mb=20  # More realistic default (not 1MB)
     fi
 
     # Theoretical maximum without safety buffer
     local theoretical_max=$((available_mb / avg_mb))
 
-    # Apply safety buffer (default 15%, refined later based on traffic patterns)
-    local safety_buffer=15
+    # Apply safety buffer (50% - much more conservative for shared hosting!)
+    # This accounts for peak traffic spikes and other processes
+    local safety_buffer=50
     local recommended=$((theoretical_max * (100 - safety_buffer) / 100))
 
-    # Sanity checks
-    if [ "$recommended" -lt 2 ]; then
-        echo "2|Minimum safe value (insufficient memory)"
-    elif [ "$recommended" -gt 500 ]; then
-        # Cap at 500 (typical proxy upstream pool size)
-        echo "500|Capped at safe maximum (would be $recommended)"
+    # Hard cap at traffic-realistic limits
+    if [ "$recommended" -lt 5 ]; then
+        echo "5|Minimum safe value (insufficient memory)"
+    elif [ "$recommended" -gt 150 ]; then
+        # CRITICAL: Cap at 150 max per domain on shared hosting
+        # Higher values require dedicated servers
+        echo "150|Capped at safe maximum for shared hosting (would be $recommended)"
     else
-        local reason="Memory-based: ${avg_mb}MB per process, ${available_mb}MB available, ${safety_buffer}% buffer"
+        local reason="Memory-based: ${avg_mb}MB per process, ${available_mb}MB available (after MySQL: ${mysql_memory_mb}MB), ${safety_buffer}% safety buffer"
         echo "$recommended|$reason"
     fi
 }