Hoist prime order thresholds in CPU heuristics

docs/ByDivisorPathMap.md

@@ -0,0 +1,35 @@
+# --mersenne=bydivisor Path Map
+
+This temporary map tracks the code paths exercised by the `--mersenne=bydivisor` mode and notes the latest review status for each branch. Entries move from _Queued_ to _Reviewed_ once the surrounding loops have been audited for invariant work.
+
+## High-level Flow
+- `EvenPerfectBitScanner` CLI parsing → _Reviewed_
+- `MersenneNumberDivisorByDivisorTester.Run` → _Reviewed_
+- `EvenPerfectBitScanner.IO.CalculationResultsFile`
+  - `LoadCandidatesWithinRange` → _Reviewed_
+  - `EnumerateCandidates` → _Reviewed_
+- `IMersenneNumberDivisorByDivisorTester` implementations
+  - `MersenneNumberDivisorByDivisorCpuTester`
+    - `IsPrime` → _Reviewed_
+    - `CheckDivisors` (128-bit path) → _Reviewed_
+    - `CheckDivisors64` → _Reviewed_
+  - `MersenneNumberDivisorByDivisorGpuTester`
+    - `IsPrime` → _Reviewed_
+    - `CheckDivisors` → _Reviewed_
+    - `DivisorByDivisorKernels.CheckKernel` → _Reviewed_
+
+- `MersenneDivisorCycles`
+  - `TryCalculateCycleLengthForExponentCpu` → _Reviewed_
+  - `TryFactorIntoCountsInternal` → _Reviewed_
+  - `PollardRho64` → _Reviewed_
+  - `ReduceOrder` (includes `ProcessReduceOrderPrime`) → _Reviewed_
+- `PrimeOrderCalculator`
+  - `InitializeStartingOrderCpu` → _Reviewed_
+  - `ExponentLoweringCpu` / `ProcessExponentLoweringPrime` → _Reviewed_
+  - `ValidateOrderAgainstFactors` / `ValidateOrderForFactor` → _Reviewed_
+  - `TryConfirmCandidateCpu` / `CheckCandidateViolation` → _Reviewed_
+  - `TryHeuristicFinishCpu` / `BuildCandidates` / `SortCandidates` → _Reviewed_
+
+## Next Steps
+- Hold for additional guidance on further --mersenne=bydivisor audits; computation branches documented above are fully reviewed.
+- Defer result aggregation and reporting reviews until instructed otherwise, keeping the focus on computation-only branches.

docs/HeuristicIsPrimePlan.md

@@ -136,7 +136,7 @@ The plan incorporates the updated divisor-class heuristics (Groups A/B, wheels,
    * [done] Kept GPU divisibility in standard modular arithmetic while reserving Montgomery transforms for CPU confirmation logic.
    * [done] When the temporary Group B gate is disabled, delegate GPU calls to the CPU fallback so Group A coverage remains in place while the accelerator path stays available for future re-enablement.
 8. [done] **Refactor by-divisor CPU/GPU testers to reuse heuristics**
-   * [done] Drove `MersenneNumberDivisorByDivisorCpuTester.CheckDivisors` from `HeuristicPrimeTester.CreateMersenneDivisorEnumerator`, eliminating the bespoke residue loop while preserving the existing status counters.
+   * [done] Drove `MersenneNumberDivisorByDivisorCpuTester.CheckDivisors` from `HeuristicPrimeTester.CreateMersenneDivisorEnumerator`, eliminating the bespoke residue loop and retiring the legacy status counter.
    * [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.