fix(s7): classic STRING/DT unrepresentable writes map to BadOutOfRange, not BadCommunicationError (#632)

S7.Net's own STRING/DT encoders throw ArgumentException; that fell into the
generic write catch (BadCommunicationError + Degraded health). Now surfaced as
S7ValueRangeException like the WSTRING/DATE codecs.

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

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -1555,14 +1555,21 @@ public sealed class S7Driver
                 // ReadScalarBlockAsync read, so WriteBytesAsync writes the whole reserved STRING. A value
                 // longer than StringLength throws ArgumentException (S7.Net rejects overflow; we do NOT
                 // silently truncate). A null value encodes as the empty string.
-                return global::S7.Net.Types.S7String.ToByteArray(Convert.ToString(value) ?? "", tag.StringLength);
+                // #632: surfaced as S7ValueRangeException (→ BadOutOfRange) like the WSTRING codec — a
+                // client value error, not a comms fault (the raw ArgumentException used to land in the
+                // generic catch as BadCommunicationError + Degraded).
+                try { return global::S7.Net.Types.S7String.ToByteArray(Convert.ToString(value) ?? "", tag.StringLength); }
+                catch (ArgumentException ex) { throw new S7ValueRangeException($"S7 STRING value does not fit the declared {tag.StringLength}-character field: {ex.Message}"); }
 
             case S7DataType.DateTime:
                 // S7.Net's DateTime.ToByteArray builds the 8-byte DT BCD block. It validates the
                 // 1990–2089 DT range and throws ArgumentOutOfRangeException for an out-of-range year —
                 // we surface that (no silent clamp). Value coerced via Convert.ToDateTime (accepts a
                 // System.DateTime or a parseable timestamp string).
-                return global::S7.Net.Types.DateTime.ToByteArray(Convert.ToDateTime(value));
+                // #632: the range refusal maps to BadOutOfRange (see STRING above).
+                var dt = Convert.ToDateTime(value);
+                try { return global::S7.Net.Types.DateTime.ToByteArray(dt); }
+                catch (ArgumentOutOfRangeException ex) { throw new S7ValueRangeException($"S7 DATE_AND_TIME value {dt:O} is outside the DT range (1990–2089): {ex.Message}"); }
 
             // Writes refuse (S7ValueRangeException → BadOutOfRange) rather than truncate or clamp.
             case S7DataType.WString: return S7ValueCodecs.EncodeWString(value, tag.StringLength);

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScalarBlockTests.cs

@@ -299,7 +299,7 @@ public sealed class S7ScalarBlockTests
     {
         var tag = Tag(S7DataType.String, stringLength: 5);
         // 6 chars into a 5-char reserved field — S7.Net throws ArgumentException.
-        Should.Throw<ArgumentException>(() => S7Driver.EncodeScalarBlock(tag, "ABCDEF"));
+        Should.Throw<S7ValueRangeException>(() => S7Driver.EncodeScalarBlock(tag, "ABCDEF"));
     }
 
     // ── String round-trip identity (encode → decode) ──────────────────────────────────────
@@ -376,7 +376,7 @@ public sealed class S7ScalarBlockTests
     {
         var tag = Tag(S7DataType.DateTime);
         var value = new System.DateTime(year, 1, 1, 0, 0, 0);
-        Should.Throw<ArgumentOutOfRangeException>(() => S7Driver.EncodeScalarBlock(tag, value));
+        Should.Throw<S7ValueRangeException>(() => S7Driver.EncodeScalarBlock(tag, value));
     }
 
     // ── DateTime round-trip identity (encode → decode) ────────────────────────────────────

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ValueCodecTests.cs

@@ -407,6 +407,35 @@ public sealed class S7ValueCodecTests
         drv.GetHealth().State.ShouldBe(DriverState.Healthy);
     }
 
+    /// <summary>
+    ///     #632 live-coverage finding: classic STRING and DT writes use S7.Net's own encoders, which throw
+    ///     <see cref="ArgumentException"/> / <see cref="ArgumentOutOfRangeException"/> for an unrepresentable
+    ///     value. That fell into the generic catch (BadCommunicationError + Degraded health) while the
+    ///     sibling WSTRING/DATE codecs return BadOutOfRange — a client error must not look like a comms fault.
+    /// </summary>
+    [Fact]
+    public async Task Classic_STRING_and_DT_unrepresentable_writes_are_BadOutOfRange_without_degrading_health()
+    {
+        var plc = new MemoryS7Plc();
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Probe = new S7ProbeOptions { Enabled = false },
+            RawTags = S7RawTags.Entries(
+                new S7TagDefinition("Str", "DB1.DBB0", S7DataType.String, StringLength: 4),
+                new S7TagDefinition("Dt", "DB1.DBB20", S7DataType.DateTime)),
+        };
+        using var drv = new S7Driver(opts, "s7-classic-range", new MemoryS7PlcFactory(plc));
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+        var ct = TestContext.Current.CancellationToken;
+
+        (await drv.WriteAsync([new WriteRequest("Str", "abcd")], ct))[0].StatusCode.ShouldBe(0u);
+        (await drv.WriteAsync([new WriteRequest("Str", "abcde")], ct))[0].StatusCode.ShouldBe(0x803C0000u);
+        (await drv.WriteAsync([new WriteRequest("Dt", new DateTime(1980, 1, 1))], ct))[0].StatusCode.ShouldBe(0x803C0000u);
+        drv.GetHealth().State.ShouldBe(DriverState.Healthy);
+        (await drv.ReadAsync(["Str"], ct))[0].Value.ShouldBe("abcd");
+    }
+
     // ---- fakes ----
 
     private sealed class MemoryS7PlcFactory(MemoryS7Plc plc) : IS7PlcFactory