gravity map: laned-belts mapped and admitted; lane host and half-width cells filled

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/aetheria-gravity-map.md

@@ -131,11 +131,11 @@ Cells not filled, plainly: whether a per-body multiplier on c or the core is eve
 | **Rock** (`Asteroid`) | (belt key, index) is the `ChunkId`. The index order is fixed at generation and never re-sorted, because wear (`ChunkWear`) is keyed by it. | Persisted (Distance, Phase, Size, RotationSpeed) about the belt's parent; wear and respawn live on Zone. | The generator draws a rock. Zone owns its wear and its pose (`AsteroidBelt.Pose`). |
 | **Period rule** | A property of the belt, not of the rock: the persisted flag `AsteroidBeltData.RidesRail` (MessagePack key 11, JSON `ridesRail`). False: each rock reads its own distance (`PeriodAround(parent, rock.Distance)`), an annulus. True: every rock takes its rail's period (`Orbits[rail].Period`), so a Trojan swarm keeps its shape (ruling `trojans-ride-host-period-with-stations`; on own-distance rails it shears within an hour, B60). | Persisted at generation. A belt saved before key 11 reads false, the annulus it was (CultCache defaults a missing slot, B61). | Zone's constructor alone writes `AsteroidBelt.Periods`, through PeriodAround or the rail's own Period; the flag only says which. Forbidden: a period formula in Pose, BeltTargets, DrawAhead, the renderer or the generator, and a second flag or shape enum read anywhere else. |
 | **Extent rule** | What a belt's rail adds to its parent's L_F: `AsteroidBelt.Extent(railDistance)`, the outermost rock for an annulus, the rail's own Distance for a swarm, whose rocks' periods never read their own distance. So a swarm moves no well (B61). An edge (Oort-like) belt must add nothing beyond the window, or the family's fade band narrows (B60). | Derived at zone build. | `AsteroidBelt.Extent`, read by Zone (the only WellNode builder in play) and by the station tests' rebuilt tree. The generator's clearance tree never sees a swarm, which is not a GeneratorPlanet. |
-| **Belt host** | A generator-time relation only. A Trojan host is a planet or gas giant (PlanetMass < mass <= SunMass) whose parent is a body, at a distance > 0. A ring member is never a host: its rail's pull adds its partners' (WellTree.PullAround), so a rail copied beside it would take another period and shear (B61). The swarm's rail copies the host's (Parent, Distance, Phase); that copy is all Zone needs, and nothing persists the host. A lane's host waits on laned-belts. | Lives for one GenerateZone call. | ZoneGenerator.GenerateZone's swarm pass. |
+| **Belt host** | A generator-time relation only. A Trojan host is a planet or gas giant (PlanetMass < mass <= SunMass) whose parent is a body, at a distance > 0. A ring member is never a host: its rail's pull adds its partners' (WellTree.PullAround), so a rail copied beside it would take another period and shear (B61). The swarm's rail copies the host's (Parent, Distance, Phase); that copy is all Zone needs, and nothing persists the host. A lane's host is a body that keeps its slot with room on both sides of the lane (cut laned-belts: half the eligible bodies, never a Trojan host, one shape per parent). | Lives for one GenerateZone call. | ZoneGenerator.GenerateZone's swarm pass. |
 | **Lagrange station orbit** | A bodyless OrbitData on a host's rail, 1/6 turn ahead of or behind it (CreateLagrangeOrbit). On a swarm host it sits inside the swarm, a mining outpost among the rocks (ruling `trojans-ride-host-period-with-stations`); rocks are on the floater layer below it, so nothing collides. | Created at generation and persisted. | ZoneGenerator's station placement, unchanged: candidacy reads the GeneratorPlanet tree, where no swarm exists, so no swarm can bar its host. |
 | **Belt generation settings** | `ZoneGenerationSettings` in Settings.asset (an LFS object): BeltProbability 0.25, BeltMassCeiling 500, AsteroidBeltWidth (a ceiling that never binds, B56), AsteroidCount = sqrt(mass x D) + 11. Trojans: TrojanProbability 0.15 per host, TrojanArc 0.07 turn per swarm, TrojanHalfWidth 0.06 D, TrojanCount = 0.04 D + 8 rocks round each of L4 and L5 (tuning defaults for a flight, B61). The code default of TrojanProbability is 0, so settings built in code draw no swarm. | Authored. | Settings.asset. Forbidden: a tunable shape's numbers as constants in code. The swarm's random stream salt is a ZoneGenerator constant, not a tunable. |
 
-Cells not filled, plainly: the lane's host set and half-width (laned-belts' map proposes the visual margin, ruling `lanes-two-sided-visual-margin`); where an edge cloud's rocks sit between a root's window and the zone boundary (edge-material's map, rulings `edge-material-root-only` and `edge-material-in-the-dark`). The edge material's place in the potential is not a question: it stays out of the extent, because the law breaks otherwise (B60).
+Cells not filled, plainly: where an edge cloud's rocks sit between a root's window and the zone boundary (edge-material's map, rulings `edge-material-root-only` and `edge-material-in-the-dark`). The edge material's place in the potential is not a question: it stays out of the extent, because the law breaks otherwise (B60).
 
 ## Rationale
 
@@ -180,5 +180,5 @@ Mapped and admitted (2026-10-14, base 11b2d7ad): `aetheria-gravity:cut_spec:cut-
 - **grid-noise-presentation**: the Sector Waves noise (after grid-lowering on layer 10, drawn only into the nebula patch height) and fine-grid detail move to non-slope presentation (grid-gravity-only-ruled); it also owns the Main Menu's own Surface Displacement brushes (B29, follow-up `menu-grid-brushes`). Waits on grid-lowering.
 - **top-speed-field**: top speed becomes a hull field; no drag below it, drag on the excess above it; the VelocityLimit clamp (Behaviors/VelocityLimit.cs) and always-on hull drag (Ship.cs:127-129) go; AI pilots brake actively; open: drag shape above the cap, consumables as modifiers, whether loot and wreckage come to rest (aetheria-gravity:ruling:no-drag-below-top-speed, target invariant orbits-do-not-decay). Waits on potential-owner and orbits-from-field.
 - **belt-shapes** (follow-up `belt-shapes`, ruling `belt-shapes-direction`; B60, B61; order by ruling `trojans-first`). One cut per shape. trojan-swarms is mapped and admitted (2026-10-18, base 67517f40): `aetheria-gravity:cut_spec:cut-trojan-swarms.r1`.
-  - **laned-belts**: only a body with room on both sides of its lane keeps a laned belt, and the lane's half-width is its own visual margin, not the placement Roche margin (ruling `lanes-two-sided-visual-margin`; 468 eligible at the Roche width, B60). Folds in `belt-after-belt-edge-pin`, in the same Place loop.
+  - **laned-belts** (mapped and admitted 2026-10-21, base d52b50f9: `aetheria-gravity:cut_spec:cut-laned-belts.r1`; lane half-width 5 body radii, a flight default): only a body with room on both sides of its lane keeps a laned belt, and the lane's half-width is its own visual margin, not the placement Roche margin (ruling `lanes-two-sided-visual-margin`; 468 eligible at the Roche width, B60). Folds in `belt-after-belt-edge-pin`, in the same Place loop.
   - **edge-material**: one sparse Oort-like cloud per root (per subzone root in a multi-root zone), from its family's window out toward the zone boundary, nothing at planets' rims (ruling `edge-material-root-only`); kept out of the extent (B60) and skipped by the populated radius, so its rocks sit in the dark fade (ruling `edge-material-in-the-dark`).