fix(csharp): compile record fields named Equals, GetHashCode, and ToString

.agents/skills/polyxml-codegen-workflow/SKILL.md

@@ -815,3 +815,9 @@ Jackson 3 sorts properties alphabetically by default. Emit `@JsonPropertyOrder`
 from flattened schema fields for its struct models, including inherited fields,
 or valid reads can produce XSD-invalid XML on writes. The Spring fixture checks
 returned XML against the source XSD independently using the JDK validator.
+
+C# positional record properties named Equals/GetHashCode/ToString collide with
+synthesized methods (UCI QueryPET's Equals field exposed CS8866). Suffix their
+identifiers with Value before applying per-struct uniqueness; preserve original
+XML names. The particle wire round-trip test covers these names and an explicit
+EqualsValue collision in both record and mutable-class modes.

crates/polyxml-core/src/codegen/csharp/mod.rs

@@ -114,6 +114,12 @@ pub fn to_csharp_property_name(raw: &str, enclosing_type: Option<&str>) -> Strin
     };
 
     let sanitized = sanitize_keyword(&safe, "csharp");
+    // Positional record members cannot shadow the synthesized equality methods.
+    let sanitized = if matches!(sanitized.as_str(), "Equals" | "GetHashCode" | "ToString") {
+        format!("{sanitized}Value")
+    } else {
+        sanitized
+    };
     if let Some(enclosing) = enclosing_type {
         if sanitized == enclosing || sanitized.trim_start_matches('@') == enclosing {
             return format!("{}Value", sanitized);

crates/polyxml-core/tests/test_csharp_codegen.rs

@@ -79,6 +79,7 @@ static DOTNET_LOCK: Mutex<()> = Mutex::new(());
 #[test]
 fn particle_wire_structure_round_trips() {
     for (schema, root, documents) in [
+        (r#"<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"><xs:element name="Query"><xs:complexType><xs:sequence><xs:element name="Equals" type="xs:string"/><xs:element name="EqualsValue" type="xs:string"/><xs:element name="GetHashCode" type="xs:string"/><xs:element name="ToString" type="xs:string"/></xs:sequence></xs:complexType></xs:element></xs:schema>"#, "Query", vec!["<Query><Equals>a</Equals><EqualsValue>b</EqualsValue><GetHashCode>c</GetHashCode><ToString>d</ToString></Query>"]),
         (include_str!("../../../research/fixtures/nested_sequence_choice.xsd"), "Root", vec!["<Root><First>A</First><Second>B</Second></Root>", "<Root><Alternative>C</Alternative></Root>"]),
         (include_str!("../../../research/fixtures/repeated_sequence.xsd"), "Root", vec!["<Root><First>A1</First><Second>B1</Second><First>A2</First><Second>B2</Second></Root>"]),
         (include_str!("../../../research/fixtures/substitution_group.xsd"), "Portfolio", vec!["<Portfolio xmlns='urn:audit:substitution'><Bond>A1</Bond><Equity>B1</Equity><Bond>A2</Bond></Portfolio>"]),