feat(csharp-scope): parity Unit 6b — member-call dedup + handled-site fix

Closes 1 parity failure (9 → 8). Adds the missing legacy-parity
behavior: collapse multiple member-call sites from the same caller
to the same target into one CALLS edge.

Changes:
- `scope-resolution/contract/scope-resolver.ts`: new optional
  `collapseMemberCallsByCallerTarget` flag. Default false (preserves
  the per-site invariant); C# sets it true.
- `scope-resolution/graph-bridge/edges.ts`: dedup key drops
  `line:col` when `collapseByCallerTarget` is on AND edgeType is
  `CALLS` (ACCESSES writes keep per-site granularity).
- `scope-resolution/passes/receiver-bound-calls.ts`: plumbs
  `collapse` through every `tryEmitEdge` call, and crucially marks
  `handledSites.add(siteKey)` whenever a resolved def was found —
  not only when the edge was freshly emitted. Otherwise the site
  leaked through to `emitReferencesViaLookup` which re-emitted a
  per-site edge, defeating the collapse.
- `languages/csharp/scope-resolver.ts`: opt in to the collapse.

Python parity 204/204 on both flag paths; legacy C# 175/175 green;
8 C# parity failures remain.

gitnexus/src/core/ingestion/languages/csharp/scope-resolver.ts

@@ -71,6 +71,11 @@ const csharpScopeResolver: ScopeResolver = {
   // since signatures are authoritative.
   fieldFallbackOnMethodLookup: false,
   propagatesReturnTypesAcrossImports: true,
+
+  // C# matches legacy DAG by collapsing member-call CALLS edges to
+  // `(caller, target)` — multiple `g.Greet(...)` sites from Main
+  // yield ONE edge, not one per site.
+  collapseMemberCallsByCallerTarget: true,
 };
 
 export { csharpScopeResolver };

gitnexus/src/core/ingestion/scope-resolution/contract/scope-resolver.ts

@@ -210,6 +210,15 @@ export interface ScopeResolver {
    */
   readonly fieldFallbackOnMethodLookup?: boolean;
 
+  /**
+   * Collapse member-call CALLS edges by `(caller, target)` rather
+   * than per-site. Default `false` (scope-resolution's contract
+   * invariant is per-site dedup). C# enables this to match the
+   * legacy DAG's member-call collapsing where multiple call sites
+   * from the same caller to the same target yield one edge.
+   */
+  readonly collapseMemberCallsByCallerTarget?: boolean;
+
   /**
    * Optional post-finalize hook to inject cross-file bindings that
    * aren't modeled via explicit imports. C# uses this to make every

gitnexus/src/core/ingestion/scope-resolution/graph-bridge/edges.ts

@@ -68,6 +68,7 @@ export function tryEmitEdge(
   reason: string,
   seen: Set<string>,
   confidence = 0.85,
+  collapseByCallerTarget = false,
 ): boolean {
   const callerGraphId = resolveCallerGraphId(site.inScope, scopes, nodeLookup);
   const targetGraphId = resolveDefGraphId(targetDef.filePath, targetDef, nodeLookup);
@@ -76,7 +77,14 @@ export function tryEmitEdge(
   if (targetGraphId === undefined) return false;
   if (edgeType === undefined) return false;
 
-  const dedupKey = `${edgeType}:${callerGraphId}->${targetGraphId}:${site.atRange.startLine}:${site.atRange.startCol}`;
+  // CALLS edges may collapse to `(caller, target)` granularity when
+  // the provider opts in (C# matches legacy DAG behavior this way).
+  // Write/read ACCESSES keep per-site dedup so multiple writes to the
+  // same field on different lines produce distinct edges.
+  const useCollapsed = collapseByCallerTarget && edgeType === 'CALLS';
+  const dedupKey = useCollapsed
+    ? `${edgeType}:${callerGraphId}->${targetGraphId}`
+    : `${edgeType}:${callerGraphId}->${targetGraphId}:${site.atRange.startLine}:${site.atRange.startCol}`;
   if (seen.has(dedupKey)) return false;
   seen.add(dedupKey);
 

gitnexus/src/core/ingestion/scope-resolution/passes/receiver-bound-calls.ts

@@ -51,7 +51,7 @@ import { resolveCompoundReceiverClass } from '../passes/compound-receiver.js';
  *  refactors lighter — callers only need to populate what we read. */
 type ReceiverBoundProviderSubset = Pick<
   ScopeResolver,
-  'isSuperReceiver' | 'fieldFallbackOnMethodLookup'
+  'isSuperReceiver' | 'fieldFallbackOnMethodLookup' | 'collapseMemberCallsByCallerTarget'
 >;
 
 export function emitReceiverBoundCalls(
@@ -69,6 +69,7 @@ export function emitReceiverBoundCalls(
   // from the reference index — see Contract Invariant I5.
   const seen = new Set<string>();
   const fieldFallback = provider.fieldFallbackOnMethodLookup ?? true;
+  const collapse = provider.collapseMemberCallsByCallerTarget === true;
 
   for (const parsed of parsedFiles) {
     const namespaceTargets = collectNamespaceTargets(parsed, scopes);
@@ -100,11 +101,15 @@ export function emitReceiverBoundCalls(
               memberDef,
               'scope-resolution: super-receiver',
               seen,
+              0.85,
+              collapse,
             );
-            if (ok) {
-              emitted++;
-              handledSites.add(siteKey);
-            }
+            if (ok) emitted++;
+            // Always mark handled when the site was resolved, even
+            // if the edge was deduplicated (collapse mode), so
+            // `emitReferencesViaLookup` doesn't re-emit from the
+            // reference index.
+            handledSites.add(siteKey);
             continue;
           }
         }
@@ -135,11 +140,15 @@ export function emitReceiverBoundCalls(
               memberDef,
               memberDef.filePath !== parsed.filePath ? 'import-resolved' : 'global',
               seen,
+              0.85,
+              collapse,
             );
-            if (ok) {
-              emitted++;
-              handledSites.add(siteKey);
-            }
+            if (ok) emitted++;
+            // Always mark handled when the site was resolved, even
+            // if the edge was deduplicated (collapse mode), so
+            // `emitReferencesViaLookup` doesn't re-emit from the
+            // reference index.
+            handledSites.add(siteKey);
             continue;
           }
         }
@@ -158,11 +167,11 @@ export function emitReceiverBoundCalls(
             memberDef,
             memberDef.filePath !== parsed.filePath ? 'import-resolved' : 'global',
             seen,
+            0.85,
+            collapse,
           );
-          if (ok) {
-            emitted++;
-            handledSites.add(siteKey);
-          }
+          if (ok) emitted++;
+          handledSites.add(siteKey);
           continue;
         }
       }
@@ -185,11 +194,11 @@ export function emitReceiverBoundCalls(
             memberDef,
             memberDef.filePath !== parsed.filePath ? 'import-resolved' : 'global',
             seen,
+            0.85,
+            collapse,
           );
-          if (ok) {
-            emitted++;
-            handledSites.add(siteKey);
-          }
+          if (ok) emitted++;
+          handledSites.add(siteKey);
           continue;
         }
       }
@@ -254,11 +263,15 @@ export function emitReceiverBoundCalls(
               memberDef,
               memberDef.filePath !== parsed.filePath ? 'import-resolved' : 'global',
               seen,
+              0.85,
+              collapse,
             );
-            if (ok) {
-              emitted++;
-              handledSites.add(siteKey);
-            }
+            if (ok) emitted++;
+            // Always mark handled when the site was resolved, even
+            // if the edge was deduplicated (collapse mode), so
+            // `emitReferencesViaLookup` doesn't re-emit from the
+            // reference index.
+            handledSites.add(siteKey);
             continue;
           }
         }
@@ -294,11 +307,14 @@ export function emitReceiverBoundCalls(
               reason,
               seen,
               confidence,
+              collapse,
             );
-            if (ok) {
-              emitted++;
-              handledSites.add(siteKey);
-            }
+            if (ok) emitted++;
+            // Always mark handled when the site was resolved, even
+            // if the edge was deduplicated (collapse mode), so
+            // `emitReferencesViaLookup` doesn't re-emit from the
+            // reference index.
+            handledSites.add(siteKey);
             continue;
           }
         }
@@ -336,11 +352,10 @@ export function emitReceiverBoundCalls(
               reason,
               seen,
               confidence,
+              collapse,
             );
-            if (ok) {
-              emitted++;
-              handledSites.add(siteKey);
-            }
+            if (ok) emitted++;
+            handledSites.add(siteKey);
           }
         }
       }