fix(pr-review): use structural is_test marker, not just name heuristics

codegraph_pr_context classified a caller as a test only when its name
matched test_*/*_test* or its path contained /tests/. Idiomatic Rust unit
tests live in `#[cfg(test)] mod tests` with descriptive names (e.g.
`weighted_mean_l2_math`, `loads_potion_f32_no_weights`), so they were
invisible and every function they cover was reported as "0 coverage".

The indexer already records `is_test` on each function node (from the
language's #[test]/@test marker; helpers.rs:112). Read it via a new
node_props::is_test accessor and prefer it over the name/path heuristics,
which remain as a fallback for languages that don't populate the marker.

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

Author: anvanster

crates/codegraph-server/src/domain/node_props.rs

@@ -109,3 +109,11 @@ pub(crate) fn is_public(node: &Node) -> bool {
         .or_else(|| node.properties.get_bool("exported"))
         .unwrap_or_else(|| matches!(visibility(node), "public" | "pub"))
 }
+
+/// Whether the node is a test function, as recorded at index time from the
+/// language's test marker (`#[test]`/`#[cfg(test)]`, `@Test`, etc.). This is
+/// the structural signal; callers should prefer it over name heuristics, which
+/// miss idiomatic test names (Rust `#[cfg(test)] mod tests { fn descriptive() }`).
+pub(crate) fn is_test(node: &Node) -> bool {
+    node.properties.get_bool("is_test").unwrap_or(false)
+}

crates/codegraph-server/src/mcp/server.rs

@@ -4104,7 +4104,13 @@ impl McpServer {
                                 if let Ok(caller) = graph.get_node(caller_id) {
                                     let cname = crate::domain::node_props::name(caller);
                                     let cfile = caller.properties.get_string("path").unwrap_or("");
-                                    let is_test = cname.to_lowercase().starts_with("test_")
+                                    // Prefer the structural is_test marker recorded at index time
+                                    // (#[test]/#[cfg(test)], @Test, …); fall back to name/path
+                                    // heuristics only for languages that don't populate it. The
+                                    // heuristics alone miss idiomatic Rust tests with descriptive
+                                    // names inside `#[cfg(test)] mod tests`.
+                                    let is_test = crate::domain::node_props::is_test(caller)
+                                        || cname.to_lowercase().starts_with("test_")
                                         || cname.to_lowercase().contains("_test")
                                         || cfile.contains("/tests/")
                                         || cfile.contains("/test_");
@@ -4132,7 +4138,11 @@ impl McpServer {
                         // #87: Test gap — function has no test callers.
                         // Skip functions that ARE tests (they don't need
                         // their own coverage) and trivial getters/setters.
-                        let fn_is_test = func_name.to_lowercase().starts_with("test_")
+                        let fn_is_test = graph
+                            .get_node(*node_id)
+                            .ok()
+                            .is_some_and(|n| crate::domain::node_props::is_test(n))
+                            || func_name.to_lowercase().starts_with("test_")
                             || func_name.to_lowercase().contains("_test")
                             || changed_rel[idx].contains("/tests/")
                             || changed_rel[idx].contains("_test.");