perf(focas): cache equipment-tag parsed addresses (no per-call reparse)

Equipment tags resolved at runtime via FocasEquipmentTagParser were not
seeded in _parsedAddressesByTagName so both ReadAsync and WriteAsync
re-parsed the raw TagConfig JSON address string on every hot-path call.
Promoted the field to ConcurrentDictionary (read + write thread safety)
and introduced ResolveParsedAddress(GetOrAdd) so the first call stores
the parse result and all subsequent calls are a cache hit. Authored tags
seeded at InitializeAsync compile and work unchanged.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
@@ -33,8 +34,10 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     private readonly EquipmentTagRefResolver<FocasTagDefinition> _resolver;
     // Per-tag-name cache of the FocasAddress parsed once at InitializeAsync. ReadAsync /
     // WriteAsync look up the pre-parsed value instead of re-parsing tag.Address on every hot
-    // call — resolves Driver.FOCAS-008.
+    // call — resolves Driver.FOCAS-008. ConcurrentDictionary is required because the poll loop
-    private readonly Dictionary<string, FocasAddress> _parsedAddressesByTagName =
+    // (ReadAsync) and the host write thread (WriteAsync) both mutate this cache when resolver-
+    // produced equipment tags are encountered for the first time.
+    private readonly ConcurrentDictionary<string, FocasAddress> _parsedAddressesByTagName =
         new(StringComparer.OrdinalIgnoreCase);
     private FocasAlarmProjection? _alarmProjection;
     // _health is read/written from multiple threads (ReadAsync, WriteAsync, ProbeLoopAsync).
@@ -230,6 +233,23 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     /// <summary>Test seam — the resolved options the factory built this driver from.</summary>
     internal FocasDriverOptions Options => _options;
 
+    /// <summary>Test seam — returns true when a parsed <see cref="FocasAddress"/> for the given
+    /// reference is present in the address cache (both authored and equipment-tag paths).</summary>
+    internal bool IsParsedAddressCached(string reference) =>
+        _parsedAddressesByTagName.ContainsKey(reference);
+
+    // Resolves a tag definition to its parsed FocasAddress, caching the result so that
+    // equipment tags (resolver-produced, not seeded at InitializeAsync) don't re-parse the
+    // address string on every ReadAsync / WriteAsync hot-path call (Driver.FOCAS-008).
+    // Throwing inside the GetOrAdd factory propagates the exception to the caller and does
+    // NOT store anything in the dictionary — consistent with the existing "fail fast on a
+    // malformed address" behaviour from the init-time validation of authored tags.
+    private FocasAddress ResolveParsedAddress(FocasTagDefinition def) =>
+        _parsedAddressesByTagName.GetOrAdd(def.Name, _ =>
+            FocasAddress.TryParse(def.Address)
+                ?? throw new InvalidOperationException(
+                    $"FOCAS tag '{def.Name}' has malformed Address '{def.Address}'."));
+
     // ---- IReadable ----
 
     /// <summary>Reads values from one or more tags asynchronously.</summary>
@@ -270,14 +290,7 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             try
             {
                 var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
-                // Parsed at InitializeAsync — defensive fallback re-parse only if the tag was
+                var parsed = ResolveParsedAddress(def);
-                // somehow not seeded (shouldn't happen, but keeps the call total).
-                if (!_parsedAddressesByTagName.TryGetValue(def.Name, out var parsed))
-                {
-                    parsed = FocasAddress.TryParse(def.Address)
-                        ?? throw new InvalidOperationException(
-                            $"FOCAS tag '{def.Name}' has malformed Address '{def.Address}'.");
-                }
                 var (value, status) = await client.ReadAsync(parsed, def.DataType, cancellationToken).ConfigureAwait(false);
 
                 results[i] = new DataValueSnapshot(value, status, now, now);
@@ -334,12 +347,7 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             try
             {
                 var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
-                if (!_parsedAddressesByTagName.TryGetValue(def.Name, out var parsed))
+                var parsed = ResolveParsedAddress(def);
-                {
-                    parsed = FocasAddress.TryParse(def.Address)
-                        ?? throw new InvalidOperationException(
-                            $"FOCAS tag '{def.Name}' has malformed Address '{def.Address}'.");
-                }
                 var status = await client.WriteAsync(parsed, def.DataType, w.Value, cancellationToken).ConfigureAwait(false);
                 results[i] = new WriteResult(status);
             }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasEquipmentTagTests.cs

@@ -64,4 +64,35 @@ public class FocasEquipmentTagTests
         r[0].StatusCode.ShouldNotBe(FocasStatusMapper.BadNodeIdUnknown);
         r[0].Value.ShouldBe((sbyte)42);
     }
+
+    /// <summary>
+    ///     Regression guard for Driver.FOCAS-008 equipment-tag path: the parsed
+    ///     <see cref="FocasAddress"/> for a resolver-produced (equipment) tag must be
+    ///     cached after the first read so subsequent reads and writes skip re-parsing
+    ///     the raw TagConfig JSON on every call.
+    /// </summary>
+    [Fact]
+    public async Task Equipment_tag_parsed_address_is_cached_after_first_read()
+    {
+        var equipRef = """{"deviceHostAddress":"focas://10.0.0.5:8193","address":"R100","dataType":"Byte"}""";
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)7 } },
+        };
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Tags = [],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "focas-eq-cache", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Before any read the parsed address must NOT be in the cache.
+        drv.IsParsedAddressCached(equipRef).ShouldBeFalse();
+
+        // After a successful read the parsed address MUST be cached.
+        var r = await drv.ReadAsync([equipRef], CancellationToken.None);
+        r[0].StatusCode.ShouldBe(FocasStatusMapper.Good);
+        drv.IsParsedAddressCached(equipRef).ShouldBeTrue();
+    }
 }