perf(native): raise native edge-building threshold to smallFilesThreshold (#940)

The hardcoded > 3 threshold for native import/call edge building
triggered on 5-file incremental builds, but the napi-rs marshaling
cost (~13ms) exceeded Rust computation savings at that scale.

Raise the threshold to use ctx.config.build.smallFilesThreshold
(default 5) so small incremental builds use the JS edge path,
aligning with the same threshold used for insertNodes and structure.

Closes #936

Impact: 1 functions changed, 5 affected

Author: carlos-alm

src/domain/graph/builder/stages/build-edges.ts

@@ -798,10 +798,11 @@ export async function buildEdges(ctx: PipelineContext): Promise<void> {
       }
     }
 
-    // Skip native import-edge path for small incremental builds (≤3 files):
-    // napi-rs marshaling overhead exceeds computation savings.
+    // Skip native import-edge path for small incremental builds: napi-rs
+    // marshaling overhead (~13ms) exceeds Rust computation savings at this scale.
     const useNativeImportEdges =
-      native?.buildImportEdges && (ctx.isFullBuild || ctx.fileSymbols.size > 3);
+      native?.buildImportEdges &&
+      (ctx.isFullBuild || ctx.fileSymbols.size > ctx.config.build.smallFilesThreshold);
     if (useNativeImportEdges) {
       const beforeLen = allEdgeRows.length;
       buildImportEdgesNative(ctx, getNodeIdStmt, allEdgeRows, native!);
@@ -821,10 +822,11 @@ export async function buildEdges(ctx: PipelineContext): Promise<void> {
       buildImportEdges(ctx, getNodeIdStmt, allEdgeRows);
     }
 
-    // Skip native call-edge path for small incremental builds (≤3 files):
-    // napi-rs marshaling overhead for allNodes exceeds computation savings.
+    // Skip native call-edge path for small incremental builds: napi-rs
+    // marshaling overhead for allNodes exceeds Rust computation savings.
     const useNativeCallEdges =
-      native?.buildCallEdges && (ctx.isFullBuild || ctx.fileSymbols.size > 3);
+      native?.buildCallEdges &&
+      (ctx.isFullBuild || ctx.fileSymbols.size > ctx.config.build.smallFilesThreshold);
     if (useNativeCallEdges) {
       buildCallEdgesNative(ctx, getNodeIdStmt, allEdgeRows, allNodesBefore, native!);
     } else {