Zone.PeriodAround is the one owner: round a body, the pull its well gives at the rail's distance
(GravityField.Acceleration); round a bodyless node, the ring law (strength of the orbits inside, plus
half of what shares the ring). Orbit.Period and AsteroidBelt.Periods are written once at zone build,
before placement; BeltTargets copies the belt's periods. A parentless orbit has no field and stands at
its phase. Fixtures lose OrbitPeriod and gain wells where their rails must move. Builds; the new
OrbitsFromFieldTests follow in the next commit.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
BeltTargets drops its own reach skip (TargetRegion.CanHold owns it) and an
empty-belt guard AsteroidBelt already makes unreachable. Tests add an
off-centre sun, whole-belt searches across the antipode, cost after time
passes, a late short step that re-keys nothing, and an entity search off the
origin.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Zone.Targets (TargetingIndex) answers Within and best-first Best over
ITargetProvider regions. EntityTargets offers the observer's VisibleEntities;
BeltTargets keys each belt's rocks into kinetic bands and bounds each segment's
annular sector for distance, bearing and visibility. Entity.VisibleChunksInReach
queries the index with DetectionReachPerVisibility, an upper bound from the
sensors' hull. Zone.ChunksNear and AsteroidBelt.InnerRadius are deleted.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
