Fix NCalc case sensitivity and add formula validation

- Normalize IF/Abs/Pow/etc. to lowercase before evaluation so AI-generated
  or manually typed uppercase function names no longer cause "Function not
  found" errors
- Add NormalizeAndValidate() which normalizes then does a parse-only check
  on save — invalid formulas are rejected with a clear error before storing
- Update AI system prompt to list all functions in lowercase and explicitly
  call out case-sensitivity; add if() to the supported function list
- Add collapsible NCalc quick-reference panel in the formula editor showing
  all operators, functions (lowercase), built-in variables, and an example

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/Interfaces/ICustomFormulaAiService.cs

@@ -19,4 +19,12 @@ public interface ICustomFormulaAiService
     /// Safe server-side only — no user-controlled code execution.
     /// </summary>
     EvaluateFormulaResponse EvaluateFormula(EvaluateFormulaRequest request);
+
+    /// <summary>
+    /// Normalizes NCalc built-in function names to lowercase (IF→if, Abs→abs, etc.) then
+    /// attempts a parse-only evaluation to catch syntax errors before the formula is saved.
+    /// Returns the normalized formula string and a null error on success, or the original
+    /// formula and an error message on failure.
+    /// </summary>
+    (string NormalizedFormula, string? Error) NormalizeAndValidate(string formula);
 }

src/PowderCoating.Infrastructure/Services/CustomFormulaAiService.cs

@@ -1,5 +1,6 @@
 using System.Text;
 using System.Text.Json;
+using System.Text.RegularExpressions;
 using NCalc2;
 using Anthropic.SDK;
 using Anthropic.SDK.Messaging;
@@ -24,8 +25,22 @@ public class CustomFormulaAiService : ICustomFormulaAiService
 
     private const string SystemPrompt = @"You are an expert pricing formula engineer for a powder coating business.
 Your job is to generate NCalc expressions that calculate either a fixed price or a surface area
-from user-supplied field values. NCalc supports standard math operators (+, -, *, /, %, Pow()),
+from user-supplied field values.
-comparison operators, and the Abs(), Round(), Max(), Min() built-in functions.
+
+CRITICAL: NCalc function names are CASE-SENSITIVE and must be ALL LOWERCASE.
+Supported built-in functions (always write these exactly as shown):
+  if(condition, trueValue, falseValue)   — conditional expression
+  abs(x)                                 — absolute value
+  round(x, digits)                       — round to N decimal places
+  max(a, b)                              — larger of two values
+  min(a, b)                              — smaller of two values
+  pow(base, exponent)                    — exponentiation
+  sqrt(x)                                — square root
+Standard operators: +  -  *  /  %
+Comparison operators: <  >  <=  >=  ==  !=
+Boolean operators: &&  ||  !
+
+Do NOT use: IF, Abs, Round, Max, Min, Pow, Sqrt (uppercase versions) — NCalc will reject them.
 
 The user will describe a custom fabricated item (e.g., 'Roof curb', 'Electrical enclosure',
 'Tubular frame') and you must produce a pricing formula template.
@@ -172,6 +187,35 @@ Rules:
         }
     }
 
+    // Lowercase NCalc built-in names before evaluation so that user-typed or AI-generated
+    // uppercase variants (IF, Abs, POW, etc.) don't produce "Function not found" errors.
+    private static readonly Regex _ncalcFuncRegex = new(
+        @"\b(if|abs|round|max|min|pow|sqrt|ceiling|floor|truncate|sign|log|exp)\b(?=\s*\()",
+        RegexOptions.IgnoreCase | RegexOptions.Compiled);
+
+    private static string NormalizeFormula(string formula) =>
+        _ncalcFuncRegex.Replace(formula, m => m.Value.ToLowerInvariant());
+
+    /// <inheritdoc />
+    public (string NormalizedFormula, string? Error) NormalizeAndValidate(string formula)
+    {
+        if (string.IsNullOrWhiteSpace(formula))
+            return (formula, "Formula cannot be empty.");
+
+        var normalized = NormalizeFormula(formula);
+        try
+        {
+            var expr = new Expression(normalized);
+            if (expr.HasErrors())
+                return (formula, expr.Error);
+            return (normalized, null);
+        }
+        catch (Exception ex)
+        {
+            return (formula, ex.Message);
+        }
+    }
+
     /// <inheritdoc />
     public EvaluateFormulaResponse EvaluateFormula(EvaluateFormulaRequest request)
     {
@@ -183,7 +227,7 @@ Rules:
             var variables = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(
                 request.VariablesJson ?? "{}") ?? new();
 
-            var expr = new Expression(request.Formula);
+            var expr = new Expression(NormalizeFormula(request.Formula));
             foreach (var kv in variables)
             {
                 expr.Parameters[kv.Key] = kv.Value.ValueKind == JsonValueKind.Number

src/PowderCoating.Web/Controllers/CompanySettingsController.cs

@@ -3054,6 +3054,10 @@ public class CompanySettingsController : Controller
         var fieldError = ValidateTemplateFields(dto.FieldsJson);
         if (fieldError != null) return Json(new { success = false, message = fieldError });
 
+        var (normalizedFormula, formulaError) = _formulaAiService.NormalizeAndValidate(dto.Formula);
+        if (formulaError != null) return Json(new { success = false, message = $"Formula error: {formulaError}" });
+        dto.Formula = normalizedFormula;
+
         var companyId = _tenantContext.GetCurrentCompanyId()!.Value;
         var entity = _mapper.Map<CustomItemTemplate>(dto);
         entity.CompanyId = companyId;
@@ -3076,6 +3080,10 @@ public class CompanySettingsController : Controller
         var fieldError = ValidateTemplateFields(dto.FieldsJson);
         if (fieldError != null) return Json(new { success = false, message = fieldError });
 
+        var (normalizedFormula, formulaError) = _formulaAiService.NormalizeAndValidate(dto.Formula);
+        if (formulaError != null) return Json(new { success = false, message = $"Formula error: {formulaError}" });
+        dto.Formula = normalizedFormula;
+
         var companyId = _tenantContext.GetCurrentCompanyId()!.Value;
         var entity = await _unitOfWork.CustomItemTemplates.GetByIdAsync(dto.Id);
         if (entity == null || entity.CompanyId != companyId)

src/PowderCoating.Web/Views/CompanySettings/Index.cshtml

@@ -2343,6 +2343,40 @@
                                 <span class="me-1">Variables (click to insert):</span>
                                 <span id="cfVariablePills"></span>
                             </div>
+                            <div class="mt-2">
+                                <a class="small text-decoration-none" data-bs-toggle="collapse" href="#cfFormulaRef" role="button">
+                                    <i class="bi bi-question-circle me-1"></i>Formula reference
+                                </a>
+                                <div class="collapse" id="cfFormulaRef">
+                                    <div class="card card-body py-2 px-3 mt-1 small border-secondary-subtle" style="font-size:.8rem">
+                                        <div class="row g-2">
+                                            <div class="col-md-6">
+                                                <strong class="d-block mb-1 text-muted text-uppercase" style="font-size:.65rem;letter-spacing:.05em">Operators</strong>
+                                                <code>+ &nbsp;- &nbsp;* &nbsp;/ &nbsp;%</code><br>
+                                                <code>&lt; &nbsp;&gt; &nbsp;&lt;= &nbsp;&gt;= &nbsp;== &nbsp;!=</code><br>
+                                                <code>&amp;&amp; &nbsp;|| &nbsp;!</code>
+                                                <strong class="d-block mt-2 mb-1 text-muted text-uppercase" style="font-size:.65rem;letter-spacing:.05em">Built-in variables (auto-injected)</strong>
+                                                <code>rate</code> &mdash; template&rsquo;s default rate<br>
+                                                <code>standard_labor_rate</code><br>
+                                                <code>markup_pct</code><br>
+                                                <code>additional_coat_labor_pct</code>
+                                            </div>
+                                            <div class="col-md-6">
+                                                <strong class="d-block mb-1 text-muted text-uppercase" style="font-size:.65rem;letter-spacing:.05em">Functions (must be lowercase)</strong>
+                                                <code>if(cond, a, b)</code> &mdash; conditional<br>
+                                                <code>abs(x)</code><br>
+                                                <code>round(x, digits)</code><br>
+                                                <code>max(a, b)</code> / <code>min(a, b)</code><br>
+                                                <code>pow(base, exp)</code><br>
+                                                <code>sqrt(x)</code>
+                                                <strong class="d-block mt-2 mb-1 text-muted text-uppercase" style="font-size:.65rem;letter-spacing:.05em">Example</strong>
+                                                <code class="d-block text-break">if(qty &gt; 10, qty * rate * 0.9, qty * rate)</code>
+                                                <span class="text-muted">10% discount over 10 units</span>
+                                            </div>
+                                        </div>
+                                    </div>
+                                </div>
+                            </div>
                         </div>
                         <div class="mb-3">
                             <label class="form-label">Notes</label>