fix(parser): persist is_test on Rust function nodes (partial)

ir_to_graph wrote is_async/is_static/is_abstract but not is_test, so the
graph never carried the marker the visitor already computes. Add it, plus a
regression test that a #[test] fn with a descriptive name inside
`#[cfg(test)] mod tests` sets is_test.

NOTE: insufficient on its own — end-to-end pr_context still misreports
coverage; is_test is not reaching the queried nodes in the real indexing
pipeline (cause not yet isolated; not a cache artifact).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: anvanster

crates/codegraph-rust/src/mapper.rs

@@ -71,7 +71,8 @@ pub fn ir_to_graph(
             .with("line_end", func.line_end as i64)
             .with("is_async", func.is_async)
             .with("is_static", func.is_static)
-            .with("is_abstract", func.is_abstract);
+            .with("is_abstract", func.is_abstract)
+            .with("is_test", func.is_test);
 
         // Add complexity metrics if available
         if let Some(ref complexity) = func.complexity {

crates/codegraph-rust/src/visitor.rs

@@ -1320,6 +1320,33 @@ fn test_something() {}
         assert!(visitor.functions[0].is_test);
     }
 
+    #[test]
+    fn test_visitor_test_fn_inside_cfg_test_mod() {
+        // The idiomatic Rust unit-test shape: a #[test] fn with a descriptive
+        // (non-`test_`) name inside `#[cfg(test)] mod tests`. This is what the
+        // PR-review coverage analysis was missing.
+        let source = r#"
+fn weighted_mean_l2() {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn weighted_mean_l2_math() {
+        weighted_mean_l2();
+    }
+}
+"#;
+        let visitor = parse_and_visit(source);
+        let t = visitor
+            .functions
+            .iter()
+            .find(|f| f.name == "weighted_mean_l2_math")
+            .expect("nested test fn should be visited");
+        assert!(t.is_test, "#[test] fn inside `mod tests` must set is_test");
+    }
+
     #[test]
     fn test_visitor_visibility_modifiers() {
         let source = r#"