test(overrides): case-variant override names verified end to end through the flattener; UI single path gets the hint (ScadaBridge#105)

Re-verified #105 item 2 on the real write paths: ManagementActor bulk attribute
overrides (CLI set-overrides / management API) and InstanceService.SetAttributeOverrideAsync
(Central UI single editor) both match the template member ordinally and refuse a
case-variant name, so nothing is stored for the flattener to drop. Native-source
overrides already validate against the flattener's own output.

- New theory tests drive each path, feed whatever it stored into the real
  FlatteningService, and assert every stored override is applied (exact-case row is
  the positive control). Mutation: accepting case variants (OrdinalIgnoreCase) fails
  them with "stored ... but the flattener dropped it as unresolved".
- The did-you-mean hint moves to TemplateEngine.OverrideNameMatching and is now also
  on the UI single-attribute path; ambiguous matches get no hint.

Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi

src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs

@@ -1170,10 +1170,7 @@ public class ManagementActor : ReceiveActor
     /// an ambiguous match gets no hint.
     /// </summary>
     internal static string CaseMismatchHint(string name, IEnumerable<string> candidates)
-    {
-        var matches = candidates.Where(c => string.Equals(c, name, StringComparison.OrdinalIgnoreCase)).Distinct(StringComparer.Ordinal).Take(2).ToList();
-        return matches.Count == 1 ? $" (names are case-sensitive; did you mean '{matches[0]}'?)" : string.Empty;
-    }
+        => OverrideNameMatching.CaseMismatchHint(name, candidates);
 
     private static async Task<object?> HandleSetInstanceOverrides(IServiceProvider sp, SetInstanceOverridesCommand cmd, AuthenticatedUser user)
     {

src/ZB.MOM.WW.ScadaBridge.TemplateEngine/OverrideNameMatching.cs

@@ -0,0 +1,32 @@
+namespace ZB.MOM.WW.ScadaBridge.TemplateEngine;
+
+/// <summary>
+/// ScadaBridge#105: instance override names address a template member by its exact
+/// (ordinal) name, because the flattener matches overrides ordinally and silently skips
+/// one it cannot resolve. Every override write path (ManagementActor bulk attribute and
+/// native-source commands, used by the CLI and the management API; and
+/// <see cref="Services.InstanceService.SetAttributeOverrideAsync"/>, used by the Central UI)
+/// therefore rejects a name that differs from a member only by case instead of storing a
+/// dead override. This helper builds the shared "did you mean" hint for that rejection.
+/// </summary>
+public static class OverrideNameMatching
+{
+    /// <summary>
+    /// Returns a hint naming the single candidate that equals <paramref name="name"/>
+    /// case-insensitively, or an empty string when there is no such candidate or the
+    /// case-insensitive match is ambiguous.
+    /// </summary>
+    /// <param name="name">The override name that did not match any member exactly.</param>
+    /// <param name="candidates">The member names the override could address.</param>
+    /// <returns>A hint suffix (leading space, no trailing period), or an empty string.</returns>
+    public static string CaseMismatchHint(string name, IEnumerable<string> candidates)
+    {
+        ArgumentNullException.ThrowIfNull(candidates);
+        var matches = candidates
+            .Where(c => string.Equals(c, name, StringComparison.OrdinalIgnoreCase))
+            .Distinct(StringComparer.Ordinal)
+            .Take(2)
+            .ToList();
+        return matches.Count == 1 ? $" (names are case-sensitive; did you mean '{matches[0]}'?)" : string.Empty;
+    }
+}

src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs

@@ -168,7 +168,9 @@ public class InstanceService
         var templateAttr = templateAttrs.FirstOrDefault(a => a.Name == attributeName);
         if (templateAttr == null)
             return Result<InstanceAttributeOverride>.Failure(
-                $"Attribute '{attributeName}' does not exist in template {instance.TemplateId}. Cannot add new attributes via overrides.");
+                $"Attribute '{attributeName}' does not exist in template {instance.TemplateId}" +
+                OverrideNameMatching.CaseMismatchHint(attributeName, templateAttrs.Select(a => a.Name)) +
+                ". Cannot add new attributes via overrides.");
 
         if (templateAttr.IsLocked)
             return Result<InstanceAttributeOverride>.Failure(