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refactor(simulation): thread SeedChain through atlas RNG callers (#952, D-224)

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generate_skeleton / compute_district_mix / derive_layout_mode /
organic_placements / derive_reservations now take a SeedChain instead of a
bare seed: u64. The two ad-hoc wrapping_add pre-mixing hacks are replaced with
real domain separation:
- district-type allocation draws from chain.derive(SeedDomain::Layer4Quarter, 0)
- organic block placement draws from chain.derive(SeedDomain::Block, 0)

DistrictSkeleton.seed now records chain.seed(); test call sites pass
SeedChain::root(N); stale seed-param docs updated.

Re-tuned all_district_types_can_appear: the seed-stream change exposed it as
latently fragile — every type has a clamped weight >= 1 (reachable), but 50
weighted draws can miss a low-weight type (Administrative) depending on the
sequence; the old seed got lucky. Raised the draw count to 500 so it tests
genuine reachability rather than a lucky sequence. Determinism-affecting by
design — this is the RNG-using layer D-224 flagged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
jpmschweitzer
2026-05-23 12:05:19 +02:00
co-authored by Claude Opus 4.7
parent de9142ce37
commit 41343987f0
2 changed files with 75 additions and 45 deletions
Download Patch File Download Diff File Expand all files Collapse all files
server/src/atlas/district_mix.rs
+33 -17
View File
@@ -12,7 +12,7 @@
//! **Determinism (D-010, D-194):** Integer weights throughout. No f32 in the
//! district count computation. Seed-driven noise uses seeded RNG.
use crate::seed::AtlasRng;
use crate::seed::{SeedChain, SeedDomain};
use crate::simulation::generator::{DistrictType, PoliticalArchetype};
// ---------------------------------------------------------------------------
@@ -172,13 +172,14 @@ pub struct DistrictMix {
/// `total_districts` is the number of districts to allocate. A good default is
/// `max(4, population_tier * 2)`.
///
/// `seed` is the city-level RNG seed (D-010 determinism).
/// `chain` is this city's position in the deterministic seed tree; the district
/// allocation draws from its `Layer4Quarter` sub-stream (D-224, D-010).
pub fn compute_district_mix(
population: i64,
economic_role: &str,
archetype: &PoliticalArchetype,
total_districts: u32,
seed: u64,
chain: SeedChain,
) -> DistrictMix {
let tier = population_tier(population);
let (transit_min, commercial_min, residential_min) = tier_guarantees(tier);
@@ -197,7 +198,7 @@ pub fn compute_district_mix(
// We avoid f32 by using integer weighted random selection.
let weight_sum: u32 = weights.iter().sum();
let mut counts: [u32; 9] = [0; 9];
let mut lcg = AtlasRng::new(seed.wrapping_add(1));
let mut lcg = chain.derive(SeedDomain::Layer4Quarter, 0).atlas_rng();
for _ in 0..total_districts {
let mut pick = lcg.next_u32() % weight_sum;
@@ -262,7 +263,7 @@ mod tests {
"manufacturing",
&PoliticalArchetype::Industrial,
8,
42,
SeedChain::root(42),
);
// total may exceed requested due to guarantees
assert!(mix.total >= 8, "district count should be >= requested");
@@ -277,7 +278,7 @@ mod tests {
"service_mixed",
&PoliticalArchetype::Pioneer,
6,
7,
SeedChain::root(7),
);
let transit = mix
.districts
@@ -312,14 +313,14 @@ mod tests {
"financial",
&PoliticalArchetype::Commission,
6,
99,
SeedChain::root(99),
);
let mix2 = compute_district_mix(
5_000_000,
"financial",
&PoliticalArchetype::Commission,
6,
99,
SeedChain::root(99),
);
assert_eq!(mix1, mix2, "same inputs must produce identical output");
}
@@ -331,10 +332,15 @@ mod tests {
"financial",
&PoliticalArchetype::Corporate,
8,
42,
SeedChain::root(42),
);
let mix_pioneer = compute_district_mix(
5_000_000,
"financial",
&PoliticalArchetype::Pioneer,
8,
SeedChain::root(42),
);
let mix_pioneer =
compute_district_mix(5_000_000, "financial", &PoliticalArchetype::Pioneer, 8, 42);
// Should differ in at least one district type count.
assert_ne!(
mix_corp.districts, mix_pioneer.districts,
@@ -344,7 +350,13 @@ mod tests {
#[test]
fn military_archetype_has_administrative() {
let mix = compute_district_mix(2_000_000, "military", &PoliticalArchetype::Military, 8, 10);
let mix = compute_district_mix(
2_000_000,
"military",
&PoliticalArchetype::Military,
8,
SeedChain::root(10),
);
let admin = mix
.districts
.iter()
@@ -358,13 +370,18 @@ mod tests {
#[test]
fn all_district_types_can_appear() {
// With enough districts and a balanced role, every type should appear at least once.
// Reachability check: every type has a clamped weight of at least 1
// (compute_district_mix `.max(1)`), so all are reachable. A large draw
// count makes every one appear regardless of the RNG sequence — a small
// count can miss a low-weight type purely by luck, which is sequence- and
// therefore seed-dependent (this is not a realistic city size).
let requested: u32 = 500;
let mix = compute_district_mix(
50_000_000,
"service_mixed",
&PoliticalArchetype::Pioneer,
50,
0,
requested,
SeedChain::root(0),
);
for dt in &DIST_COLS {
let present = mix
@@ -373,8 +390,7 @@ mod tests {
.any(|d| std::mem::discriminant(d) == std::mem::discriminant(dt));
assert!(
present,
"DistrictType {:?} never appeared in 50-district mix",
dt
"DistrictType {dt:?} never appeared in {requested}-district mix"
);
}
}
server/src/atlas/skeleton_gen.rs
+42 -28
View File
@@ -20,7 +20,7 @@
use crate::atlas::block_irregularity::block_irregularity;
use crate::atlas::district_mix::{compute_district_mix, population_tier};
use crate::seed::AtlasRng;
use crate::seed::{SeedChain, SeedDomain};
use crate::simulation::generator::{
BlockPlacement, BlockSkeleton, CityGenerationContext, ComplexityTier, DistrictId,
DistrictLayoutMode, DistrictSkeleton, DistrictType, MultiBlockReservation, PoliticalArchetype,
@@ -39,14 +39,14 @@ use crate::simulation::generator::{
/// - `economic_role`: Economic role string (one of the 10 canonical values).
/// - `district_id`: Content-addressable identifier for this district.
/// - `founding_age_years`: Years since founding — controls block irregularity.
/// - `seed`: Deterministic seed for this district (derived from master seed via SeedChain).
/// - `chain`: This district's position in the deterministic seed tree (D-224 SeedChain).
pub fn generate_skeleton(
context: &CityGenerationContext,
population: i64,
economic_role: &str,
district_id: DistrictId,
founding_age_years: u32,
seed: u64,
chain: SeedChain,
) -> DistrictSkeleton {
// ── 1. SettingType ────────────────────────────────────────────────────
// Pass through the surrounding_biome from context — it already encodes
@@ -59,7 +59,7 @@ pub fn generate_skeleton(
// ── 3. DistrictLayoutMode ─────────────────────────────────────────────
let irregularity = block_irregularity(founding_age_years, &context.political_archetype);
let layout_mode = derive_layout_mode(&context.political_archetype, irregularity, seed);
let layout_mode = derive_layout_mode(&context.political_archetype, irregularity, chain);
// ── 4. District mix → block grid ─────────────────────────────────────
// A single district occupies a 4×4 block grid = 16 blocks.
@@ -69,11 +69,11 @@ pub fn generate_skeleton(
economic_role,
&context.political_archetype,
total_blocks,
seed,
chain,
);
// ── 5. Multi-block reservations ───────────────────────────────────────
let reservations = derive_reservations(tier, economic_role, seed);
let reservations = derive_reservations(tier, economic_role, chain);
// Build the reservation lookup: block position → reservation id.
let mut block_reservation: [[Option<ReservationId>; 4]; 4] = [[None, None, None, None]; 4];
@@ -105,7 +105,7 @@ pub fn generate_skeleton(
DistrictSkeleton {
district_id,
seed,
seed: chain.seed(),
district_type: district_type_from_mix(&primary_district_type),
context: String::new(), // stub — DistrictContext = String
world_tier: context.world_tier.clone(),
@@ -223,7 +223,7 @@ fn derive_complexity(world_tier: &WorldTier, pop_tier: u8, population: i64) -> C
fn derive_layout_mode(
archetype: &PoliticalArchetype,
irregularity: f32,
seed: u64,
chain: SeedChain,
) -> DistrictLayoutMode {
match archetype {
PoliticalArchetype::Commission
@@ -233,7 +233,7 @@ fn derive_layout_mode(
PoliticalArchetype::Pioneer | PoliticalArchetype::Industrial => {
// Organic: generate per-block offsets and rotations seeded from district seed.
let placements = organic_placements(irregularity, seed);
let placements = organic_placements(irregularity, chain);
DistrictLayoutMode::Organic { placements }
}
}
@@ -243,9 +243,9 @@ fn derive_layout_mode(
///
/// Uses a seeded LCG; offset range controlled by `irregularity` (0.05–1.0)
/// scaled to the ±16 sim tile maximum from `block_irregularity::max_offset_sim_tiles`.
fn organic_placements(irregularity: f32, seed: u64) -> [[BlockPlacement; 4]; 4] {
fn organic_placements(irregularity: f32, chain: SeedChain) -> [[BlockPlacement; 4]; 4] {
let max_offset = (irregularity * 16.0) as i16;
let mut lcg = AtlasRng::new(seed.wrapping_add(0x9e37_79b9_7f4a_7c15));
let mut lcg = chain.derive(SeedDomain::Block, 0).atlas_rng();
// Build the 2D array using a flat closure to keep things readable.
let mut flat: [BlockPlacement; 16] = core::array::from_fn(|_| BlockPlacement {
@@ -362,7 +362,7 @@ fn density_for_zoning(zoning: &ZoningType) -> u8 {
fn derive_reservations(
pop_tier: u8,
economic_role: &str,
_seed: u64,
_chain: SeedChain,
) -> Vec<MultiBlockReservation> {
let mut out = Vec::new();
@@ -429,14 +429,14 @@ mod tests {
fn setting_station_passthrough() {
let mut ctx = make_context(PoliticalArchetype::Commission, WorldTier::Regional);
ctx.surrounding_biome = SettingType::Station;
let sk = generate_skeleton(&ctx, 500_000, "institutional", 1, 200, 42);
let sk = generate_skeleton(&ctx, 500_000, "institutional", 1, 200, SeedChain::root(42));
assert!(matches!(sk.setting, SettingType::Station));
}
#[test]
fn setting_urban_for_city_on_planet() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Regional);
let sk = generate_skeleton(&ctx, 500_000, "financial", 1, 200, 42);
let sk = generate_skeleton(&ctx, 500_000, "financial", 1, 200, SeedChain::root(42));
assert!(matches!(sk.setting, SettingType::Urban));
}
@@ -444,14 +444,14 @@ mod tests {
fn complexity_epicenter_high_pop_is_full() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Epicenter);
// 10M pop → pop_tier = 1 → Full on Epicenter
let sk = generate_skeleton(&ctx, 10_000_000, "financial", 1, 200, 42);
let sk = generate_skeleton(&ctx, 10_000_000, "financial", 1, 200, SeedChain::root(42));
assert_eq!(sk.complexity, ComplexityTier::Full);
}
#[test]
fn complexity_waypoint_tiny_pop_is_empty() {
let ctx = make_context(PoliticalArchetype::Pioneer, WorldTier::Waypoint);
let sk = generate_skeleton(&ctx, 1_000, "residential", 1, 50, 42);
let sk = generate_skeleton(&ctx, 1_000, "residential", 1, 50, SeedChain::root(42));
assert_eq!(sk.complexity, ComplexityTier::Empty);
}
@@ -459,7 +459,7 @@ mod tests {
fn complexity_backwater_low_pop_is_moderate() {
let ctx = make_context(PoliticalArchetype::Pioneer, WorldTier::Backwater);
// 50_000 pop → pop_tier = 0 → Moderate on Backwater (D-218: not budget-capped)
let sk = generate_skeleton(&ctx, 50_000, "residential", 1, 50, 42);
let sk = generate_skeleton(&ctx, 50_000, "residential", 1, 50, SeedChain::root(42));
assert_eq!(sk.complexity, ComplexityTier::Moderate);
}
@@ -467,7 +467,7 @@ mod tests {
fn complexity_backwater_high_pop_is_full() {
let ctx = make_context(PoliticalArchetype::Pioneer, WorldTier::Backwater);
// 10M pop → pop_tier = 1 → Full on Backwater (D-218: not budget-capped)
let sk = generate_skeleton(&ctx, 10_000_000, "residential", 1, 50, 42);
let sk = generate_skeleton(&ctx, 10_000_000, "residential", 1, 50, SeedChain::root(42));
assert_eq!(sk.complexity, ComplexityTier::Full);
}
@@ -475,28 +475,28 @@ mod tests {
fn complexity_passage_low_pop_is_minimal() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Passage);
// 50_000 pop → pop_tier = 0 → Minimal on Passage (transit stop, budget-capped)
let sk = generate_skeleton(&ctx, 50_000, "transit_hub", 1, 100, 42);
let sk = generate_skeleton(&ctx, 50_000, "transit_hub", 1, 100, SeedChain::root(42));
assert_eq!(sk.complexity, ComplexityTier::Minimal);
}
#[test]
fn layout_commission_is_grid() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Regional);
let sk = generate_skeleton(&ctx, 500_000, "institutional", 1, 100, 99);
let sk = generate_skeleton(&ctx, 500_000, "institutional", 1, 100, SeedChain::root(99));
assert!(matches!(sk.layout_mode, DistrictLayoutMode::Grid));
}
#[test]
fn layout_pioneer_is_organic() {
let ctx = make_context(PoliticalArchetype::Pioneer, WorldTier::Regional);
let sk = generate_skeleton(&ctx, 500_000, "residential", 1, 400, 99);
let sk = generate_skeleton(&ctx, 500_000, "residential", 1, 400, SeedChain::root(99));
assert!(matches!(sk.layout_mode, DistrictLayoutMode::Organic { .. }));
}
#[test]
fn block_grid_is_fully_populated() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Regional);
let sk = generate_skeleton(&ctx, 500_000, "financial", 1, 200, 42);
let sk = generate_skeleton(&ctx, 500_000, "financial", 1, 200, SeedChain::root(42));
// All 16 blocks must have valid positions.
for row in 0..4 {
for col in 0..4 {
@@ -511,7 +511,7 @@ mod tests {
fn no_reservations_for_small_city() {
let ctx = make_context(PoliticalArchetype::Pioneer, WorldTier::Backwater);
// pop_tier 0, not transit_hub → no reservations.
let sk = generate_skeleton(&ctx, 80_000, "residential", 1, 50, 42);
let sk = generate_skeleton(&ctx, 80_000, "residential", 1, 50, SeedChain::root(42));
assert!(sk.reservations.is_empty());
}
@@ -519,7 +519,7 @@ mod tests {
fn park_reservation_for_large_city() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Epicenter);
// 100M pop → pop_tier 2 → park reservation.
let sk = generate_skeleton(&ctx, 100_000_000, "financial", 1, 300, 42);
let sk = generate_skeleton(&ctx, 100_000_000, "financial", 1, 300, SeedChain::root(42));
let has_park = sk
.reservations
.iter()
@@ -531,7 +531,7 @@ mod tests {
fn transit_terminal_for_transit_hub_role() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Regional);
// pop_tier 0 but transit_hub → terminal reservation.
let sk = generate_skeleton(&ctx, 80_000, "transit_hub", 1, 200, 42);
let sk = generate_skeleton(&ctx, 80_000, "transit_hub", 1, 200, SeedChain::root(42));
let has_terminal = sk
.reservations
.iter()
@@ -543,7 +543,7 @@ mod tests {
fn reserved_blocks_linked_in_grid() {
let ctx = make_context(PoliticalArchetype::Commission, WorldTier::Epicenter);
// 100M pop → park at (1,2),(1,3),(2,2),(2,3) with reservation id 1.
let sk = generate_skeleton(&ctx, 100_000_000, "financial", 1, 300, 42);
let sk = generate_skeleton(&ctx, 100_000_000, "financial", 1, 300, SeedChain::root(42));
// All park blocks must reference the park reservation (id=1).
for &(row, col) in &[(1u8, 2u8), (1, 3), (2, 2), (2, 3)] {
let b = &sk.blocks[row as usize][col as usize];
@@ -557,8 +557,22 @@ mod tests {
#[test]
fn determinism_same_seed_same_output() {
let ctx = make_context(PoliticalArchetype::Industrial, WorldTier::Regional);
let sk1 = generate_skeleton(&ctx, 2_000_000, "manufacturing", 77, 250, 12345);
let sk2 = generate_skeleton(&ctx, 2_000_000, "manufacturing", 77, 250, 12345);
let sk1 = generate_skeleton(
&ctx,
2_000_000,
"manufacturing",
77,
250,
SeedChain::root(12345),
);
let sk2 = generate_skeleton(
&ctx,
2_000_000,
"manufacturing",
77,
250,
SeedChain::root(12345),
);
// Compare block grid zoning and positions.
for row in 0..4 {
for col in 0..4 {