docs(union): describe first-class union nodes

CHANGELOG.md

@@ -17,7 +17,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
-- Unions are now indexed in C, C++, Objective-C and Rust. A `union` declaration previously produced no symbol at all, so it never appeared in search or `codegraph_explore`, and anything attached to it disappeared with it — in Rust, every `impl SomeTrait for MyUnion` lost its edge, and the methods from that impl were left pointing at a type the graph did not contain. A `typedef union { … } Name;` in C now carries the typedef's name like `typedef struct` already did. Re-index after upgrading to pick up the new symbols.
+- C, C++, Objective-C and Rust unions are now indexed as first-class `union` nodes. A `union` declaration previously produced no symbol at all, so it never appeared in search or `codegraph_explore`, and anything attached to it disappeared with it — in Rust, every `impl SomeTrait for MyUnion` lost its edge, and the methods from that impl were left pointing at a type the graph did not contain. A `typedef union { … } Name;` in C now carries the typedef's name and remains distinguishable from a struct. Re-index after upgrading to replace the earlier struct-shaped union nodes.
 
 - `codegraph_explore` now concentrates its answer on the code that actually answers your question instead of spreading it across files that merely share a word with it, so more of the answer arrives in a single call. Thanks @LeDuyViet for the detailed measurements and reproduction. (#1500)
 - Files only weakly related to your question now come back as a name, symbol and line number instead of spending the answer on their source — name one of them in a follow-up `codegraph_explore` to get it back in full. (#1500)

CLAUDE.md

@@ -66,7 +66,7 @@ The public API surface is `src/index.ts` — the `CodeGraph` class wires all the
 
 Defined in `src/types.ts`. Both extractors and resolvers must use these exact strings.
 
-- **NodeKind**: `file`, `module`, `class`, `struct`, `interface`, `trait`, `protocol`, `function`, `method`, `property`, `field`, `variable`, `constant`, `enum`, `enum_member`, `type_alias`, `namespace`, `parameter`, `import`, `export`, `route`, `component`.
+- **NodeKind**: `file`, `module`, `class`, `struct`, `interface`, `trait`, `protocol`, `function`, `method`, `property`, `field`, `variable`, `constant`, `enum`, `enum_member`, `type_alias`, `namespace`, `parameter`, `import`, `export`, `route`, `component`, `union`.
 - **EdgeKind**: `contains`, `calls`, `imports`, `exports`, `extends`, `implements`, `references`, `type_of`, `returns`, `instantiates`, `overrides`, `decorates`.
 
 ### Multi-agent installer

docs/design/ccpp-kernel-port-checklist.md

@@ -139,10 +139,9 @@ walker mirrors, with file:line anchors (as of `705e501`). Read WITH
 ## Extractor configs (languages/c-cpp.ts — read the whole file when porting)
 
 **cExtractor (line 180):** functionTypes=[function_definition]; NO
-class/method/interface types; structTypes=[struct_specifier]
-(superseded: `union_specifier` joined structTypes — a named `union U { … };`
-is a definition, extracted with kind `struct`, and `typedef union { … } N;`
-resolves through resolveTypeAliasKind like `typedef struct`);
+class/method/interface types; structTypes=[struct_specifier];
+unionTypes=[union_specifier] (a named `union U { … };` is a definition, and
+`typedef union { … } N;` resolves to a first-class `union` node);
 enumTypes=[enum_specifier]; enumMemberTypes=[enumerator];
 typeAliasTypes=[type_definition]; importTypes=[preproc_include];
 callTypes=[call_expression]; variableTypes=[declaration];

docs/design/rust-lang-kernel-port-checklist.md

@@ -54,9 +54,9 @@ Types: functionTypes=[`function_item`, **`function_signature_item`**] (the
 latter = a trait method DECLARATION `fn render(&self);` — extracted so a
 trait's method set is first-class); classTypes=[] (impl blocks instead);
 methodTypes = same two; interfaceTypes=[`trait_item`] with
-**interfaceKind:'trait'**; structTypes=[`struct_item`] (superseded:
-`union_item` joined structTypes — same `body` field, same extractor, kind
-`struct`); enumTypes=[`enum_item`];
+**interfaceKind:'trait'**; structTypes=[`struct_item`];
+unionTypes=[`union_item`] (same body walk, distinct `union` node kind);
+enumTypes=[`enum_item`];
 enumMemberTypes=[`enum_variant`]; typeAliasTypes=[`type_item`];
 importTypes=[`use_declaration`]; callTypes=[`call_expression`];
 variableTypes=[`let_declaration`, `const_item`, `static_item`].