§3 landed — separatrix / separatrix_average multiplicity collapse

Evergreen: sn-boundary-averaged-name-multiplicity · landed 2026-07-10 · deterministic graph ops only (no LLM recompose; $0 of the authorised budget spent)

Before → after

Metric	Before	After
Averaged leaves with 2–3 live names	24	0 (84 leaves total, all single-name)
Cross-subtree collisions (surface-varying bases)	15	0
Locus-stripped names	6	0
Shared flux-function names (correct, by design)	3	4 (+ `magnetic_shear_at_plasma_boundary`, now two DD sources)
Live grammar-gate violations	1	0
Provenance orphans / edge-scalar desyncs	0 / 0	0 / 0

Actions applied (46, all verified against full source sets first)

6 rename cascades (target absent): 3 locus-stripped FSA names gained _at_plasma_boundary; oxygen_density_at_plasma_boundary and the drafted toroidal_ion_velocity_at_plasma_boundary structure name gained the FSA prefix; post-move, toroidal_plasma_momentum_at_plasma_boundary → toroidal_flux_surface_averaged_total_plasma_momentum_at_plasma_boundary.
27 supersede-merges: short/stripped duplicates onto the canonical FSA name (name_stage='superseded', superseded_by, HAS_SUCCESSOR + REFINED_FROM edges, sources re-pointed). Includes flux_surface_averaged_magnetic_shear onto the shared magnetic_shear_at_plasma_boundary.
11 targeted source moves (collisions — the short name STAYS as the local leaf's): iron/nitrogen densities, dt/iron velocities, five velocity_tor species, and the momentum pair.
2 detach + deterministic create (collided leaves with no donor name): flux_surface_averaged_effective_charge_at_plasma_boundary and flux_surface_averaged_ion_density_at_plasma_boundary persisted through the pipeline write path as name_stage='drafted' — the next routine sn run review rotation scores them.

Momentum "swap" resolution

momentum_phi/momentum_tor are a DD v3/v4 alias pair (tor obsolescent 3.42, removed 4.0) — both leaves denote the SAME total toroidal momentum, so each subtree's two leaves now share one name: local → toroidal_total_plasma_momentum_at_plasma_boundary (2 sources), averaged → toroidal_flux_surface_averaged_total_plasma_momentum_at_plasma_boundary (2 sources). Same alias treatment already held for velocity_phi/velocity_tor species pairs.

Generalisation check

No live maximum_over_flux_surface/minimum_over_flux_surface names exist; the §4 gate bans them on flux-function bases at composition.
summary/volume_average/*: 26 leaves / 27 names, near 1:1 — explicitly scoped OUT (a volume average of a flux function is not a no-op).
Post-collapse reconcile: rederive_structural_edges (18 dead edges cleared, 2 migrated), resolve_doc_links (54 links repointed, 11 removed), 0 orphans / 0 desyncs, gate audit clean.

Anomaly noted (out of scope)

Both separatrix*/q leaves map to safety_factor_at_normalized_poloidal_magnetic_flux_equal_to_0_95 — q95, but the separatrix is ψ_N=1.0. The flux-function sharing is correct; the locus value looks wrong. Queued as followup f-bam-004.