fix(ablegacy): final review I3 — default reverts to libplctag; Native is opt-in

On a wire the native PCCC path is proven only for N-file reads/writes and
one F8 read (ab_server). An absent transport key now resolves to Libplctag
for every family; explicit Native still wins and still warns once per
instance on PLC-5/LogixPccc. AdminUI dropdown, CLI help, evidence claims
(PcccFileType, AbLegacy.md wire-evidence table, release note) corrected:
S:0 (default probe) and B/T/C/R/S/L/ST/A/O/I are unverified natively.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyTransportResolver.cs

@@ -4,16 +4,13 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
 
 /// <summary>
 ///     The ONE place an AbLegacy driver's effective transport is decided from its configured
-///     <see cref="AbLegacyDriverOptions.Transport"/> and its devices. The driver constructor, the Test
-///     Connect probe and the CLI (through the driver) all resolve through here.
-///     <para>An absent key means <see cref="AbLegacyTransport.Native"/> — UNLESS any configured device is a
-///     <see cref="AbLegacyPlcFamily.Plc5"/> or <see cref="AbLegacyPlcFamily.LogixPccc"/>, whose native support
-///     is limited (PLC-5: N-file reads only; LogixPccc: framing unverified). The tag factory is chosen once
-///     per DRIVER, not per device, so one such device resolves the whole driver to
-///     <see cref="AbLegacyTransport.Libplctag"/>. An explicit value always wins (an operator choice).</para>
-///     <para>The probe resolves from the config it is GIVEN. The AdminUI merges only the probed device into
-///     that config, so in a mixed-family defaulted driver Test Connect on an SLC device can resolve Native
-///     while the deployed driver resolves Libplctag (documented in docs/drivers/AbLegacy.md).</para>
+///     <see cref="AbLegacyDriverOptions.Transport"/>. The driver constructor, the Test Connect probe and the
+///     CLI (through the driver) all resolve through here.
+///     <para>An absent key means <see cref="Default"/> = <see cref="AbLegacyTransport.Libplctag"/> for EVERY
+///     family (final review I3): on a wire the native PCCC path is proven only for N-file reads and writes
+///     and one F8 read, so Native stays opt-in. An explicit value always wins (an operator choice). An
+///     explicit Native on a PLC-5 / LogixPccc device is allowed but logs a once-per-instance Warning
+///     (<see cref="NativeLimitedFamilies"/>).</para>
 /// </summary>
 public static class AbLegacyTransportResolver
 {
@@ -32,16 +29,13 @@ public static class AbLegacyTransportResolver
         return [.. devices.Select(d => d.PlcFamily).Where(IsNativeLimited).Distinct()];
     }
 
-    /// <summary>Returns the effective transport for a configured value and device set.</summary>
+    /// <summary>The transport an absent / null <c>transport</c> key selects (all families).</summary>
+    public const AbLegacyTransport Default = AbLegacyTransport.Libplctag;
+
+    /// <summary>Returns the effective transport: an explicit value always wins; null means <see cref="Default"/>.</summary>
     /// <param name="configured">The configured transport, or null for "use the default".</param>
-    /// <param name="devices">The configured devices.</param>
     /// <returns>The transport the driver runs on.</returns>
-    public static AbLegacyTransport Resolve(AbLegacyTransport? configured, IEnumerable<AbLegacyDeviceOptions> devices)
-    {
-        ArgumentNullException.ThrowIfNull(devices);
-        if (configured is { } explicitValue) return explicitValue;
-        return devices.Any(d => IsNativeLimited(d.PlcFamily)) ? AbLegacyTransport.Libplctag : AbLegacyTransport.Native;
-    }
+    public static AbLegacyTransport Resolve(AbLegacyTransport? configured) => configured ?? Default;
 
     /// <summary>Returns the effective transport for <paramref name="options"/>.</summary>
     /// <param name="options">The driver options.</param>
@@ -49,19 +43,15 @@ public static class AbLegacyTransportResolver
     public static AbLegacyTransport Resolve(AbLegacyDriverOptions options)
     {
         ArgumentNullException.ThrowIfNull(options);
-        return Resolve(options.Transport, options.Devices);
+        return Resolve(options.Transport);
     }
 
     /// <summary>
-    ///     Operator-facing description of the configured-vs-effective transport for the init log line, e.g.
-    ///     <c>Native (default)</c>, <c>Libplctag (default; PLC-5/LogixPccc device present)</c> or
-    ///     <c>Native (configured)</c>.
+    ///     Operator-facing description of the configured-vs-effective transport for the init log line:
+    ///     <c>Libplctag (default)</c> when the key was absent, <c>Native (configured)</c> when explicit.
     /// </summary>
     /// <param name="configured">The configured transport, or null.</param>
-    /// <param name="effective">The effective transport.</param>
     /// <returns>A short description.</returns>
-    public static string Describe(AbLegacyTransport? configured, AbLegacyTransport effective) =>
-        configured is not null ? $"{effective} (configured)"
-        : effective == AbLegacyTransport.Libplctag ? $"{effective} (default; PLC-5/LogixPccc device present)"
-        : $"{effective} (default)";
+    public static string Describe(AbLegacyTransport? configured) =>
+        configured is null ? $"{Resolve(configured)} (default)" : $"{configured} (configured)";
 }