diff --git a/server/csharp/MetaObjects.Codegen.Tests/ScalarArrayCodegenTests.cs b/server/csharp/MetaObjects.Codegen.Tests/ScalarArrayCodegenTests.cs
index ba498bb0f..863cbea08 100644
--- a/server/csharp/MetaObjects.Codegen.Tests/ScalarArrayCodegenTests.cs
+++ b/server/csharp/MetaObjects.Codegen.Tests/ScalarArrayCodegenTests.cs
@@ -48,6 +48,19 @@ public class ScalarArrayCodegenTests
     ]}}
     """;
 
+    // An entity with a field.uuid isArray:true — array-ness is derived, not via
+    // the removed dbColumnType:uuid_array value (Phase 1 slim-and-derive).
+    private const string UuidArrayModel = """
+    { "metadata.root": { "package": "acme", "children": [
+      { "object.entity": { "name": "Widget", "children": [
+        { "source.rdb": { "@table": "widgets" } },
+        { "field.long": { "name": "id" } },
+        { "field.uuid": { "name": "refs", "isArray": true } },
+        { "identity.primary": { "@fields": "id" } }
+      ]}}
+    ]}}
+    """;
+
     // An entity with both a scalar enum (no isArray) and an enum-array, so we can
     // assert the scalar path is unchanged (regression guard).
     private const string MixedEnumModel = """
@@ -188,6 +201,38 @@ public void Enum_array_field_does_not_emit_has_conversion_without_element_type_i
         Assert.DoesNotContain("Statuses).HasConversion<string>()", dbCtx);
     }
 
+    // -------------------------------------------------------------------------
+    // field.uuid isArray — Phase 1 slim-and-derive: array-ness via isArray:true,
+    // not the removed dbColumnType:uuid_array value.
+    // ScalarFor("uuid") == "Guid", so the existing scalar-array path handles this.
+    // -------------------------------------------------------------------------
+
+    [Fact]
+    public void Uuid_array_field_emits_ICollection_Guid_property()
+    {
+        var ctx = Ctx(Load(UuidArrayModel));
+        var src = Assert.Single(new EntityGenerator().Generate(ctx)).Content;
+
+        // field.uuid isArray:true → ICollection<Guid> with List<Guid> initializer.
+        Assert.Contains("public ICollection<Guid> Refs { get; set; } = new List<Guid>();", src);
+        // Guard: the scalar form must NOT appear.
+        Assert.DoesNotContain("public Guid? Refs", src);
+        Assert.DoesNotContain("public Guid Refs", src);
+    }
+
+    [Fact]
+    public void Uuid_array_field_emits_PrimitiveCollection_in_dbcontext()
+    {
+        var ctx = Ctx(Load(UuidArrayModel));
+        var dbCtx = Assert.Single(new DbContextGenerator().Generate(ctx)).Content;
+
+        // EF Core 8 primitive collection API for the uuid array (derived, not via
+        // the removed dbColumnType:uuid_array value).
+        Assert.Contains(
+            "modelBuilder.Entity<Widget>().PrimitiveCollection(x => x.Refs);",
+            dbCtx);
+    }
+
     // -------------------------------------------------------------------------
     // Compile check — generated scalar-array entity must be valid C#
     // -------------------------------------------------------------------------
@@ -208,6 +253,14 @@ public void Generated_enum_array_entity_compiles()
         AssertCompiles(src, "enumarray");
     }
 
+    [Fact]
+    public void Generated_uuid_array_entity_compiles()
+    {
+        var ctx = Ctx(Load(UuidArrayModel));
+        var src = Assert.Single(new EntityGenerator().Generate(ctx)).Content;
+        AssertCompiles(src, "uuidarray");
+    }
+
     // -------------------------------------------------------------------------
     // Helpers
     // -------------------------------------------------------------------------
diff --git a/server/csharp/MetaObjects.Conformance.Tests/R6Plan2LoaderTests.cs b/server/csharp/MetaObjects.Conformance.Tests/R6Plan2LoaderTests.cs
index 51a63f1ae..0d8077ec7 100644
--- a/server/csharp/MetaObjects.Conformance.Tests/R6Plan2LoaderTests.cs
+++ b/server/csharp/MetaObjects.Conformance.Tests/R6Plan2LoaderTests.cs
@@ -134,6 +134,26 @@ public void DbColumnType_unknown_value_is_ERR_BAD_ATTR_VALUE()
         Assert.Contains("allowed", err.Message);
     }
 
+    // ------------------------------------------------------------------------
+    // Phase 1 slim-and-derive: uuid_array + text_array are removed values.
+    // They now fall through Rule 1 (unknown value) → ERR_BAD_ATTR_VALUE.
+    // Array-ness is derived from field.uuid/field.string isArray:true instead.
+    // ------------------------------------------------------------------------
+
+    [Theory]
+    [InlineData("uuid_array")]
+    [InlineData("text_array")]
+    public void DbColumnType_removed_array_values_are_ERR_BAD_ATTR_VALUE(string removedValue)
+    {
+        var json = Pairing(FIELD_SUBTYPE_STRING, removedValue);
+        var res = LoadJson(json);
+        var err = res.Errors.FirstOrDefault(e =>
+            e.Code == ErrorCode.ERR_BAD_ATTR_VALUE && e.Message.Contains("dbColumnType"));
+        Assert.NotNull(err);
+        Assert.Contains(removedValue, err!.Message);
+        Assert.Contains("allowed", err.Message);
+    }
+
     // ------------------------------------------------------------------------
     // Plan 2b — own-only: an INHERITED @dbColumnType is not re-validated against
     // the inheriting field's subtype (mirrors the field.enum own-only policy).
diff --git a/server/csharp/MetaObjects/Loader/ValidationPasses.cs b/server/csharp/MetaObjects/Loader/ValidationPasses.cs
index ca0bc0213..d4cba2519 100644
--- a/server/csharp/MetaObjects/Loader/ValidationPasses.cs
+++ b/server/csharp/MetaObjects/Loader/ValidationPasses.cs
@@ -1854,8 +1854,7 @@ private static void WalkDbColumnType(MetaData node, List<MetaError> errors)
                 // Rule 2: legal (subtype × value) pairing.
                 var requiredSubType = value switch
                 {
-                    DB_COLUMN_TYPE_UUID or DB_COLUMN_TYPE_JSONB
-                        or DB_COLUMN_TYPE_UUID_ARRAY or DB_COLUMN_TYPE_TEXT_ARRAY => FIELD_SUBTYPE_STRING,
+                    DB_COLUMN_TYPE_UUID or DB_COLUMN_TYPE_JSONB => FIELD_SUBTYPE_STRING,
                     DB_COLUMN_TYPE_TIMESTAMP_TZ => FIELD_SUBTYPE_TIMESTAMP,
                     _ => null, // unreachable (Rule 1)
                 };
diff --git a/server/csharp/MetaObjects/Persistence/Db/DbConstants.cs b/server/csharp/MetaObjects/Persistence/Db/DbConstants.cs
index 6148bd99b..368e17fe1 100644
--- a/server/csharp/MetaObjects/Persistence/Db/DbConstants.cs
+++ b/server/csharp/MetaObjects/Persistence/Db/DbConstants.cs
@@ -51,6 +51,8 @@ public static class DbConstants
     /// Physical DB column-type override on a field (<c>@dbColumnType</c>). Closed value
     /// set: <see cref="DB_COLUMN_TYPE_UUID"/> / <see cref="DB_COLUMN_TYPE_JSONB"/> /
     /// <see cref="DB_COLUMN_TYPE_TIMESTAMP_TZ"/>.
+    /// Array-ness is derived from <c>isArray: true</c> on the field, not from a separate
+    /// <c>uuid_array</c>/<c>text_array</c> value (removed in Phase 1 of the slim-and-derive pass).
     /// </summary>
     public const string FIELD_ATTR_DB_COLUMN_TYPE = "dbColumnType";
 
@@ -60,10 +62,6 @@ public static class DbConstants
     public const string DB_COLUMN_TYPE_JSONB        = "jsonb";
     /// <summary><c>@dbColumnType: timestamp_with_tz</c> — <c>timestamp with time zone</c> column (legal on field.timestamp).</summary>
     public const string DB_COLUMN_TYPE_TIMESTAMP_TZ = "timestamp_with_tz";
-    /// <summary><c>@dbColumnType: uuid_array</c> — native Postgres <c>uuid[]</c> array column (legal on field.string).</summary>
-    public const string DB_COLUMN_TYPE_UUID_ARRAY   = "uuid_array";
-    /// <summary><c>@dbColumnType: text_array</c> — native Postgres <c>text[]</c> array column (legal on field.string).</summary>
-    public const string DB_COLUMN_TYPE_TEXT_ARRAY   = "text_array";
 
     /// <summary>The closed set of legal <c>@dbColumnType</c> values.</summary>
     public static readonly IReadOnlyList<string> VALID_DB_COLUMN_TYPES = new[]
@@ -71,7 +69,5 @@ public static class DbConstants
         DB_COLUMN_TYPE_UUID,
         DB_COLUMN_TYPE_JSONB,
         DB_COLUMN_TYPE_TIMESTAMP_TZ,
-        DB_COLUMN_TYPE_UUID_ARRAY,
-        DB_COLUMN_TYPE_TEXT_ARRAY,
     };
 }