fix(code-review): resolve Batch 2 open findings (AbCip, AbLegacy, Galaxy, FOCAS)

- Driver.AbCip.Contracts-001: parse 'writable' from TagConfig JSON (default true) instead of hardcoding
- Driver.AbCip.Contracts-002/-003: Dt type comment; drop dead [Display]/[Range] annotations
- Driver.AbCip.Contracts-004: dedicated AbCipEquipmentTagParser test class (+15)
- Driver.AbCip-017: document Tick severity Low-fallback on Bad severity read
- Driver.AbLegacy.Contracts-002/-003/-004: isArray-scalar remarks (+tests), MaxTagBytes/ForFamily docs
- Driver.Galaxy.Browser-003 + Driver.Galaxy.Contracts-003: extract ResolveApiKey -> GalaxySecretRef (dedup)
- Driver.Galaxy-019: cache buffered-interval only on Ok + ILogger warnings + ClassifyIntervalReply (+tests)
- Driver.FOCAS.Contracts-002: thread WriteIdempotent through DiscoverAsync (+test)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyEquipmentTagParser.cs

@@ -12,6 +12,17 @@ public static class AbLegacyEquipmentTagParser
     /// <param name="reference">The equipment tag's TagConfig JSON (also used as the def identity).</param>
     /// <param name="def">The transient definition when parsing succeeds.</param>
     /// <returns><see langword="true"/> when <paramref name="reference"/> is an AbLegacy address object.</returns>
+    /// <remarks>
+    /// <para>
+    ///     When <c>isArray</c> is the JSON literal <see langword="true"/> but <c>arrayLength</c> is
+    ///     absent, zero, or negative, the result is silently a <b>scalar</b>
+    ///     (<see cref="AbLegacyTagDefinition.ArrayLength"/> is <see langword="null"/>).
+    ///     A valid positive <c>arrayLength</c> is required to produce an array tag; <c>isArray:true</c>
+    ///     alone is not sufficient.  This is intentional: a stale length behind a cleared or absent
+    ///     <c>isArray</c> flag must never produce an orphan array tag that mismatches its scalar OPC UA
+    ///     node (see in-source comment, review C-2).
+    /// </para>
+    /// </remarks>
     public static bool TryParse(string reference, out AbLegacyTagDefinition def)
     {
         def = null!;

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyPlcFamilyProfile.cs

@@ -7,12 +7,25 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
 public sealed record AbLegacyPlcFamilyProfile(
     string LibplctagPlcAttribute,
     string DefaultCipPath,
+    /// <summary>
+    ///     Reserved for future array-length clamping.  <b>Not currently enforced anywhere in the
+    ///     driver.</b>  The values are approximate upper bounds derived from PCCC packet payload
+    ///     limits (e.g. SLC 5/05 240 bytes is the PCCC-over-EIP data cap, not a libplctag fragment
+    ///     limit).  Do not rely on this field for sizing decisions until an enforcement point is added.
+    /// </summary>
     int MaxTagBytes,
     bool SupportsStringFile,
     bool SupportsLongFile)
 {
     /// <summary>Gets the profile for the specified PLC family.</summary>
     /// <param name="family">The PLC family.</param>
+    /// <remarks>
+    ///     Any unrecognised <paramref name="family"/> value (e.g. an integer cast to the enum, or a
+    ///     value added to <see cref="AbLegacyPlcFamily"/> before this switch is updated) silently
+    ///     returns the <see cref="Slc500"/> profile.  This is intentional: it preserves
+    ///     forward-compatibility for device configs authored against a build that predates a new
+    ///     family enum member, preferring a safe default over a startup exception.
+    /// </remarks>
     public static AbLegacyPlcFamilyProfile ForFamily(AbLegacyPlcFamily family) => family switch
     {
         AbLegacyPlcFamily.Slc500 => Slc500,