fix: normalize closed-form Smagorinsky strain magnitude

docs/development/les_normalization_candidate.md

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+# Minimal Smagorinsky normalization integration candidate
+
+This local candidate changes only the two closed-form D2Q9/D3Q19 coefficients
+from 18 to 18 sqrt(2), plus their convention comments. The intended convention
+is |S| = sqrt(2 S:S), with self-consistent effective tau. No Cs default,
+iterative formula/cap/iteration count, collision dispatch, AMR guard, inlet,
+channel-parity rule, or unrelated source file changes.
+
+The resulting turbulence_smag.cuh SHA256 is
+`a3db46c2e7d27530b2d1436e65cdbed0b72cc7e047bfbeef2a640877271b51aa`,
+exactly the independently reviewed temporary correction used in the paired
+scalar and end-to-end flow experiments. Its uncorrected baseline remains at
+validation checkpoint `9805383f9c50d867e8555471baf5dbda8333a652`.
+
+## Evidence and limits
+
+The separately audited scalar-helper GPU diagnostic on the cd3 source campaign
+covered 48 cases per variant. All 32 paired iterative results were bit-identical;
+maximum patched closed-form error was approximately 1.19e-7, versus 0.06454 for
+the baseline against the same standard convention. This is scalar evidence,
+not full-collision or turbulence qualification.
+
+The independently reviewed wall-bounded, x-periodic SRT/shifted-FP32/double-buffer
+shear experiment distinguished baseline from corrected source under identical
+predeclared criteria. Baseline Cs=1 SGS decrement errors at the last two
+checkpoints were approximately 28.50% and 28.05%; corrected errors were 0.0628%
+and 0.00612%. Corrected maximum Cs=1 profile error was approximately 0.11344%,
+and the Cs=0 observations were identical between variants. Cs=1 is an amplified
+normalization diagnostic, not a recommended physical coefficient. These data
+qualify this bounded normalization comparison, not general turbulence accuracy.
+
+The current direct-header host regression uses the existing independent
+Hermite tensor construction and quadratic bisection oracle. It covers 120
+parameter subcases across D2/D3, Cs=0/.16, rho=.7/1/1.3, tau0=.56/.8,
+equilibrium, both signs of shear and trace-free extension, including a 3D axis.
+It also checks converged iterative agreement, Cs=0 omega guard bounds, and
+explicitly proves that removing sqrt(2) in temporary headers fails the oracle.
+No stored candidate header or full solver fixture is added.
+
+MRT full-trace/bulk coupling, forcing/Guo correction, other streaming/storage
+paths, three-dimensional turbulent flows, and AMR LES remain uncertified.
+Full-stress closed form and deviatoric/capped iteration intentionally need not
+agree on isotropic or cap-active stresses. Existing guards remain unchanged.
+
+## Run and retain provenance
+
+From this candidate checkout:
+
+    PYTHONPATH=src python tests/unit/test_smagorinsky_normalization.py -v
+    PYTHONPATH=src python tests/unit/test_les_flow_runner.py -v
+
+The flow runner already supports `--variant corrected` against the exact
+reviewed helper hash. Its source-pin tests now exercise that current variant;
+they still verify that the archived baseline variant rejects the corrected
+source and that unrelated source tampering is rejected.
+
+Historical Re100, Jet, matched-DFG and paired-scalar manifests/runners are not
+repinned or weakened. Their baseline-source guards are expected to reject this
+changed production tree. Run those archived source-specific checks on the clean
+9805383 checkpoint; their old GPU evidence does not become evidence for this
+candidate. The new direct-current-header test is the regression for corrected
+production. Do not describe the historical full suite as passing on this tree.
+
+Before publication or main integration, obtain final independent diff review
+and rerun the applicable scalar/flow GPU commands on the exact final candidate
+commit after the executor reconnects. Retain new checkout/import/source-hash
+receipts and compare against the frozen baseline using separate processes.
+A new commit receipt is required even though its corrected header matches the
+previously tested temporary correction. No GPU rerun, publication, or main
+merge is claimed by this candidate preparation.