Inline legacy GPU sieve and update heuristic fallbacks

EvenPerfectBitScanner.Benchmarks/PrimeTesterBenchmarks.cs

@@ -86,7 +86,7 @@ public class PrimeTesterBenchmarks
 
         for (int i = 0; i < values.Length; i++)
         {
-            if (PrimeTester.IsPrimeGpuFallback(values[i], cancellationToken))
+            if (PrimeTester.Exclusive.IsPrimeGpu(values[i], cancellationToken))
             {
                 primeCount++;
             }

PerfectNumbers.Core/HeuristicPrimeTester.cs

@@ -102,7 +102,7 @@ public sealed class HeuristicPrimeTester
     {
         if (!EnableHeuristicPrimeTesting)
         {
-            return PrimeTester.IsPrimeGpuFallback(n, ct);
+            return PrimeTester.Exclusive.IsPrimeGpu(n, ct);
         }
 
         return IsPrimeGpu(n);
@@ -119,7 +119,7 @@ public sealed class HeuristicPrimeTester
     {
         if (!EnableHeuristicPrimeTesting)
         {
-            return PrimeTester.IsPrimeGpuFallback(n, CancellationToken.None);
+            return PrimeTester.Exclusive.IsPrimeGpu(n, CancellationToken.None);
         }
 
         return HeuristicIsPrimeGpuCore(n, sqrtLimit, nMod10);

PerfectNumbers.Core/PrimeTester.cs

@@ -72,18 +72,14 @@ public sealed class PrimeTester
         return Exclusive.IsPrimeGpu(n, CancellationToken.None);
     }
 
-    public static bool IsPrimeGpu(ulong n, ulong limit, byte nMod10)
-    {
-        return Exclusive.IsPrimeGpu(n, CancellationToken.None);
-    }
+    // Legacy overload retained for heuristic toggles; tests and benchmarks now call the thread-local instance directly.
+    // public static bool IsPrimeGpu(ulong n, ulong limit, byte nMod10)
+    // {
+    //     return Exclusive.IsPrimeGpu(n, CancellationToken.None);
+    // }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public bool IsPrimeGpu(ulong n, CancellationToken ct)
-    {
-        return IsPrimeGpuFallback(n, ct);
-    }
-
-    public static bool IsPrimeGpuFallback(ulong n, CancellationToken ct)
     {
         bool forceCpu = GpuContextPool.ForceCpu;
         Span<ulong> one = stackalloc ulong[1];

docs/HeuristicIsPrimePlan.md

@@ -140,7 +140,7 @@ The plan incorporates the updated divisor-class heuristics (Groups A/B, wheels,
    * [done] Streamed GPU batches from the same enumerator and Montgomery preparation data, removing the filtered-divisor scratch arrays while continuing to feed the existing kernel and hit bookkeeping.
 9. [done] **Route legacy prime checks through heuristics**
    * [done] Introduce `HeuristicPrimeTester` so heuristic CPU/GPU checks live alongside the legacy `PrimeTester` implementations while callers opt in explicitly.
-   * [done] Maintain legacy paths for benchmarking via `PrimeTester.IsPrimeInternal`, `PrimeTester.IsPrimeGpuFallback`, and the global `HeuristicPrimeTester.EnableHeuristicPrimeTesting` switch so benchmark harnesses can compare behaviours.
+   * [done] Maintain legacy paths for benchmarking via `PrimeTester.IsPrimeInternal`, `PrimeTester.Exclusive.IsPrimeGpu`, and the global `HeuristicPrimeTester.EnableHeuristicPrimeTesting` switch so benchmark harnesses can compare behaviours.
 10. **Validation and benchmarking**
     * Create targeted unit tests covering boundary cases for Group A/B transitions, wheel enumerations, residue deltas, and the stop-on-hit behaviour.
     * Expand GPU test harnesses to assert equivalence between CPU/GPU heuristics on sampled composite and prime inputs and to verify the residue-stream contract with by-divisor sessions.

docs/HeuristicIsPrimeSpecification.md

@@ -62,7 +62,7 @@ No other endings are allowed or reordered.
 ## Default Prime Tester Entry Points
 
 * `PrimeTester.IsPrime` and `PrimeTester.IsPrimeGpu` continue to run the legacy trial-division and GPU sieve paths. Use `HeuristicPrimeTester` when the heuristic CPU/GPU flow is required.
-* Toggle `HeuristicPrimeTester.EnableHeuristicPrimeTesting` or fall back to `PrimeTester.IsPrimeInternal` / `PrimeTester.IsPrimeGpuFallback` to control heuristic rollouts in test harnesses.
+* Toggle `HeuristicPrimeTester.EnableHeuristicPrimeTesting` or fall back to `PrimeTester.IsPrimeInternal` / `PrimeTester.Exclusive.IsPrimeGpu` to control heuristic rollouts in test harnesses.
 * Benchmark harnesses can compare behaviours by calling the legacy helpers on `PrimeTester` alongside the heuristic equivalents on `HeuristicPrimeTester`.
 
 ## Integration with the By-Divisor Pipeline