Angle is geometry.
Occupancy is description.

angleRadians = normalize(atan2(dy, dx)) ∈ [0, 2π)
angleDegrees = angleRadians × 180 / π

radius = 0 → direction undefined → N_A
angle  = 0 → valid eastward direction → OK

No angle is treated as semantic importance, hierarchy, mass or quality.

occupancyCount    = count(ASSIGNED subjects in sector)
occupancyFraction = occupancyCount / applicableAngularSubjectCount

0 occupied subjects is valid numeric 0.
It does not imply a defect or low quality.

Tests cover exact root/hub/radius lineage, atan2 normalization, hub-direction N_A semantics, cyclic gaps, explicit wrap-around sectors, boundary inclusion, ambiguity preservation, occupancy zeros, immutable attachment and 23.04/Topic24 firewalls.

{
  "module": "Compo 23.03",
  "name": "angular_spacing_sector_occupancy",
  "version": "1.0-canonical",
  "canonical_main_title": "Angular spacing / sector occupancy",
  "topic": "23_РАДИАЛЬНЫЙ_БАЛАНС_И_ЦЕНТРАЛЬНЫЕ_СИСТЕМЫ",
  "scope": "EXACT_COMPO23_00_ROOT_COMPO23_01_HUB_AND_COMPO23_02_RADIUS_LINEAGE_DERIVED_POLAR_ANGLES_EXPLICIT_ANGULAR_SECTORS_CYCLIC_GAP_DESCRIPTORS_AND_NONSCORING_SECTOR_OCCUPANCY_ONLY_WITHOUT_APPROXIMATION_TARGET_FIT_SCORING_OR_GENERATION",
  "main_topic_contract": {
    "topic_title": "Радиальный баланс и центральные системы",
    "topic_goal": "Формализует радиальные композиции: hub, rings, radius bands, angular sectors и распределение элементов вокруг центра.",
    "expected_output": "RadialGroupDescriptor, hub, rings, sectors",
    "planned_files": [
      "23.00 Radial system schema",
      "23.01 Hub/center detection",
      "23.02 Radius bands and orbital groups",
      "23.03 Angular spacing / sector occupancy",
      "23.04 Scoring, generator and tests"
    ]
  },
  "ownership": {
    "owner": "Compo23.03",
    "owns": [
      "RadialAngularObservation",
      "RadialAngularObservationSet",
      "RadialAngularSpacingDescriptor",
      "RadialAngularSpacingSet",
      "RadialAngularSectorDefinition",
      "RadialSectorMembershipClass taxonomy",
      "RadialSectorAssignment",
      "RadialSectorOccupancyDescriptor",
      "RadialAngularSectorSet",
      "RadialAngularSectorPolicy",
      "RadialAngularSectorAttachment",
      "exact atan2-derived polar angle normalization to [0, 2π)",
      "deterministic cyclic angular ordering and adjacent-gap derivation",
      "explicit angular-sector membership including wrap-around sectors",
      "sector occupancy counts/fractions as non-scoring descriptors",
      "identity/status/provenance rules for Topic23 angular layer",
      "non-mutating correction request for angular/sector lineage"
    ],
    "does_not_own": [
      "RadialSystemSchema / RadialSystemSeed identity — Compo23.00",
      "hub detection / hub truth — Compo23.01",
      "radius observations, radius bands, rings and orbital groups — Compo23.02",
      "raw point geometry or foreign position identities — upstream geometry owners",
      "approximate angle/radius tolerance, target fit, scoring, MetricResult or generator — Compo23.04",
      "symmetric balance / mirror correspondence — Topic21",
      "visual center of mass, moments and counterweights — Topic22",
      "hierarchy, dominance, semantic importance, beautyScore or final-layout ranking",
      "foreign geometry/style/semantic mutation"
    ]
  },
  "consumes": [
    "exact Compo23.00 root bundle",
    "exact Compo23.01 RadialHubDescriptor + RadialHubAttachment lineage",
    "exact Compo23.02 RadialRadiusObservationSet containing dx/dy/radius lineage",
    "optional explicit RadialAngularSectorDefinition[] and bounded policy"
  ],
  "provides": [
    "RadialAngularObservation[]",
    "RadialAngularObservationSet",
    "RadialAngularSpacingDescriptor[]",
    "RadialAngularSpacingSet",
    "RadialAngularSectorDefinition[]",
    "RadialSectorAssignment[]",
    "RadialSectorOccupancyDescriptor[]",
    "RadialAngularSectorSet",
    "RadialAngularSectorAttachment"
  ],
  "owns_metrics": [],
  "independent_numeric_votes": 0,
  "status_semantics": {
    "OK": "valid exact local angular/sector descriptor",
    "N_A": "missing/conflicting/ambiguous/not-applicable evidence; never numeric zero",
    "INVALID": "malformed or impossible record; never numeric zero"
  },
  "angle_rules": [
    "angleRadians = normalize(atan2(dy, dx)) into [0, 2π)",
    "angleDegrees = angleRadians × 180 / π",
    "radius=0 makes direction undefined -> N_A; angle is not coerced to zero",
    "east=0, north=π/2, west=π, south=3π/2 in the bound coordinate frame",
    "no orientation desirability is inferred"
  ],
  "spacing_rules": [
    "only OK angular observations participate in cyclic order",
    "order is angle ascending with subjectRef lexical tie-break used only for deterministic identity",
    "adjacent cyclic gaps are in [0, 2π] and exact zero is valid for coincident rays",
    "with at least two applicable observations, cyclic gaps sum to 2π within floating arithmetic tolerance",
    "gap size is a descriptor, not rhythm quality or target fit"
  ],
  "sector_policy": {
    "definitionMode": "EXPLICIT_ARCS_ONLY",
    "membershipMode": "EXACT_ANGLE_ONLY",
    "multipleMatchMode": "N_A_NO_GUESS",
    "gapMode": "UNASSIGNED_OK",
    "maxAngularObservations": [
      1,
      4096
    ],
    "maxSectors": [
      0,
      512
    ],
    "maxSpacingDescriptors": [
      0,
      4096
    ],
    "overflow": "N_A_WITHOUT_TRUNCATION",
    "autoSectorDiscovery": false,
    "autoTolerance": false,
    "autoEqualSpacingTarget": false,
    "autoScoring": false
  },
  "sector_rules": [
    "sector start/end angles must each be in [0,2π)",
    "start < end defines a non-wrapping arc; start > end defines a wrap-around arc crossing 0",
    "start == end is INVALID because full-circle intent must not be inferred",
    "boundary inclusion is explicit per endpoint",
    "zero occupied subjects is valid occupancyCount=0",
    "overlapping explicit sectors may make one subject AMBIGUOUS -> N_A; no source/confidence winner",
    "uncovered angle -> UNASSIGNED with OK status; not a quality failure"
  ],
  "root_attachment_contract": {
    "radialSystemSeedRef": "exact Compo23.00 seed lineage",
    "hubDescriptorRef": "exact Compo23.01 descriptor identity",
    "radiusObservationSetRef": "exact Compo23.02 radius set identity",
    "angularObservationSetRef": "exact Compo23.03 angular set identity",
    "angularSpacingSetRef": "exact Compo23.03 spacing set identity",
    "angularSectorSetRef": "exact Compo23.03 sector set identity",
    "rootMutation": false,
    "metricResultRefs": []
  },
  "firewalls": [
    "angle != radius",
    "angle != hierarchy or semantic importance",
    "angle=0 is valid east direction, not N_A",
    "radius=0 direction is N_A, not angle 0",
    "coincident rays may have exact zero angular gap",
    "zero gap != zero score",
    "equal angular spacing != automatically good",
    "unequal angular spacing != automatically bad",
    "sector occupancy count != visual mass",
    "empty sector != defect",
    "full sector != quality",
    "angular sector != orbital group",
    "angular sector != symmetry class",
    "wrap-around sector != approximation",
    "multiple sector match -> N_A, not winner selection",
    "descriptor != score",
    "N_A != 0",
    "INVALID != 0",
    "heuristic != law",
    "local != global",
    "geometry != interpretation",
    "correction request != foreign mutation"
  ],
  "topic23ProgressAfterThisModule": "4/5 local",
  "next_module": "Compo 23.04 — Scoring, generator and tests",
  "hard_stop": "No 23.04 implementation in this file"
}