nx_pkg_solve.nx

nx_pkg_solve.nx -- GATE: VERSION-CONSTRAINT DEPENDENCY SOLVING (closes the PACKAGE-MGMT census gap "version- constraint solving"). Reworks nx_pkg (transitive-closure + topo + sha) with the piece it lacked: a real BACKTRACKING resolver over a package UNIVERSE where each package has multiple VERSIONS and each (package,version) declares dependency CONSTRAINTS (semver: exact / >= / caret ^ / tilde ~ / range). Grounded on the banked field research (pp_semver/pp_dephell/pp_sat/pp_backtracking): pick a version of every needed package satisfying ALL dependents' constraints jointly; backtrack on conflict; report unsatisfiable. Complete search, highest-version- first => deterministic (lockfile-stable). Constraints held as inclusive [lo,hi] intervals over encoded versions. T1 DIAMOND: App->B^1,C^1; B->D>=1.2; C->D in[1.5,2.0) -> D resolves to the HIGHEST feasible (1.9.0) via intersection. T2 BACKTRACK: App->B(any),D=1.3.0; B2.0.0->D>=1.5.0 (fails D=1.3.0) -> solver BACKTRACKS to B1.0.0 (the lower ver). T3 CONFLICT: B->D<2.0.0, C->D>=2.0.0 -> UNSATISFIABLE detected (no version of D satisfies both). T4 teeth: the semver operators (exact/gte/caret/tilde) map to the correct intervals (KATs). T5 determinism: the diamond solved twice -> identical selection (reproducible / lockfile-stable). expect_exit: 0 Sovereign: nx_syscalls. NEVER-BRICK: pure resolution, writes 0 firmware.