C# reference graph overmatches common same-name member calls

[Widthdom]

Dogfood audit finding from codex/dogfood-audit-20260623.

Observed

The C# graph appears to attribute member calls to unrelated local functions that share the same simple name. This pollutes references, hotspots, and likely impact.

Examples from dogfooding:

• references Combine --exact-name returns many Path.Combine(...) calls as references to a local Combine helper.
• hotspots reports Combine in WorkerProcessCleanupDiagnostics.cs with thousands of references.
• Similar overmatches were seen for local/helper names such as GetString, Max, Join, and Replace, where BCL/extension/member calls are counted against unrelated project symbols.

Expected

Reference extraction should account for receiver/declaring type or otherwise suppress obvious BCL/common-member false positives. At minimum, graph consumers should avoid treating Path.Combine, Math.Max, string.Join, JsonElement.GetString, etc. as references to unrelated same-name local functions.

Impact

This weakens several high-value workflows: hotspot ranking, impact analysis, reference lookup, and dead-code triage.

[Widthdom]

Latest graph dogfood found a concrete overmatch example:

• hotspots --json --limit 20 --exclude-tests reports WorkerProcessCleanupDiagnostics.Combine with reference_count: 3962.
• The actual local helper is called once from TryKill.
• references WorkerProcessCleanupDiagnostics.Combine --exact-name --exclude-tests still returns Path.Combine(...) call sites.
• callers Combine --exact-name --exclude-tests also aggregates callers of Path.Combine under the local helper name.

This looks like the same C# same-name member overmatch class, but it now affects references, callers, impact, and hotspot ranking in a very visible way.

[Widthdom]

Work started on branch fix-issue3894-3912-3915.