fix(native): restore cargo test --lib green (#978)

Three pre-existing failures surfaced by `cargo test --lib`, none of
which CI catches (CI only runs `cargo check --workspace`):

- `tree-sitter-scala 0.25` and `tree-sitter-swift 0.7` emit ABI-15
  grammars, but the workspace pins `tree-sitter = "0.24"` (supports up
  to ABI-14). Loading either grammar raised `LanguageError { version:
  15 }`, breaking all 10 Scala/Swift extractor tests. Downgrade to the
  last 0.24-compatible releases (0.24.1 / 0.6.0).

- `BuildSettings` derived `Default`, which gave `incremental: false`
  via `bool::default()`. `BuildConfig::build` is `#[serde(default)]`,
  so deserializing `{}` fell through to `BuildSettings::default()` and
  disagreed with the `#[serde(default = "default_true")]` field
  attribute. Implement `Default` manually so both paths agree.

Full suite now: 176 passed, 0 failed (was 165 passed, 11 failed).

docs check acknowledged — change is an internal grammar-crate
downgrade and a Default-impl bug fix; no user-facing API, language
support, or architecture change.

Author: carlos-alm

Cargo.lock

@@ -25,8 +25,8 @@ tree-sitter-php = "0.23"
 tree-sitter-c = "0.23"
 tree-sitter-cpp = "0.23"
 tree-sitter-kotlin-sg = "0.4"
-tree-sitter-swift = "0.7"
-tree-sitter-scala = "0.25"
+tree-sitter-swift = "0.6"
+tree-sitter-scala = "0.24"
 tree-sitter-bash = "0.23"
 tree-sitter-hcl = "1"
 tree-sitter-elixir = "0.3"

crates/codegraph-core/Cargo.toml

@@ -23,7 +23,7 @@ pub struct BuildConfig {
     pub aliases: std::collections::HashMap<String, String>,
 }
 
-#[derive(Debug, Clone, Deserialize, Default)]
+#[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct BuildSettings {
     /// Whether incremental builds are enabled (default: true).
@@ -35,6 +35,18 @@ pub struct BuildSettings {
     pub drift_threshold: f64,
 }
 
+// Manual impl so `BuildSettings::default()` matches the serde field defaults.
+// `#[derive(Default)]` would give `incremental: false`, which disagrees with
+// `#[serde(default = "default_true")]` when the outer `build` key is absent.
+impl Default for BuildSettings {
+    fn default() -> Self {
+        Self {
+            incremental: default_true(),
+            drift_threshold: default_drift_threshold(),
+        }
+    }
+}
+
 fn default_true() -> bool {
     true
 }