planetsim/CLAUDE.md

# CLAUDE.md

Guidance for Claude Code when working in this repository.

## Project

A C++/raylib simulation/game for creating semi-realistic fantasy & sci-fi
worlds/planets. Built in phases. Between phases the user can edit the world
or trigger events (meteor impact, magical events, sci-fi terraforming).

**Core principle:** the planet geometry is FIXED. Cells (vertices/faces) never
move. Only their *properties* flow over the fixed grid (Eulerian, not
Lagrangian). This keeps the data structure stable across all phases and makes
erosion, climate and drift far simpler to implement later.

## Roadmap

The project has two big arcs. **World Creation** builds a plausible planet through a
set of geological/environmental stages that **overlap and run together on a geological
clock** (My) — they are not strict sequential "phases" (the code keeps `phase*` names
internally for save/config compatibility, but think of them as continuous stages). Once
a world is "done", the long-term goal is a separate **Live World** mode that runs the
finished planet at a *much* slower, real-time-ish clock (hours/days/weeks/months) with
dynamic weather and life.

**World Creation (geological clock, mostly done):**
- **Tectonics & landmass** *(done)* — icosphere geometry, plate assignment, boundary
  stress forming mountains (convergent) and trenches/rifts (divergent). The initial
  "forming" pass settles to isostatic equilibrium, then plate motion continues.
- **Continental drift & erosion** *(done)* — real plate motion (cm/yr, My), the plate
  lifecycle (fission, stalemate kick, spreading-born plates, merging), diffusive
  erosion + a sea-level controller (~30% land), taller persistent mountains
  (collision + arc + isostatic persistence), seafloor aging→depth. `planet.cfg` +
  `planet.save`. See [[phase2-design-direction]].
- **Hydrology** *(done)* — rivers, lakes and fluvial erosion as a macro drainage network
  (depression-fill→lakes, steepest-descent→rivers, mass-conserving stream-power
  incision). Runs at a finer timestep alongside continuing drift. See [[phase3-hydrology]].
- **Climate** *(done)* — continuous per-cell temperature + orographic precipitation
  (`Planet::computeClimate`); runs from forming onward (a live "base climate" that
  updates as terrain changes). Color modes `6`/`7`.
- **Biomes** *(done)* — per-cell `Cell.biome` (13 biomes incl. polar Ice) from elevation
  + the climate fields (`Planet::classifyBiomes`), color mode `5`, saved per cell.
- **Biota — flora, fauna & funga** *(done — see `docs/fauna-flora-plan.md` +
  `docs/fauna_generation_plan.md`)* — two layers: per-cell **density scalars** (flora,
  fauna, funga ∈ [0,1]) derived from the climate fields each tick (drive the colour views),
  plus a discrete **slot/point population** of broad archetypes (Class/Order/Family/Size),
  generated **on demand** (`L`) and **saved** (save v7). Fauna is a herbivore/carnivore/
  omnivore food chain (predators gated on local prey); funga uses a flora-like but
  moisture/organic-matter-led rule. The living/evolving ecosystem is reserved for Live World.
- **Seasons (obliquity)** *(done)* — `axialTilt` drives per-cell summer/winter temperatures
  (`computeClimate`: `sTempSummer`/`sTempWinter` = annual mean ± a tilt/latitude/continentality
  amplitude); winter temp feeds the Tundra/Taiga biome cutoffs (`biomeSeasonWeight`). Static
  fields (the live yearly cycle is reserved for Live World). Color key `6` cycles the temp views.

> Durable design context (module layout, save format, climate/biome model, conventions)
> lives in **`docs/design-notes.md`** — important because Claude's auto-memory does not
> travel with the repo.

**Live World (in progress):** with planet creation finished, run the world at a slow real-time
scale with dynamic **weather** (clouds, rain, storms, fronts), day/night, and living
**ecosystems / civilization** evolving in real time. This is a separate large effort;
the fixed-grid Eulerian model + the climate fields are the groundwork for it.
- **Clock + day/night groundwork** *(done — see `PlanetLive.cpp`)* — a slow real-time clock
  (hours → weeks/months, `liveTime`/`liveRate`, key `W` to enter once settled, `[`/`]` ramp
  the rate), a moving **day/night terminator** (sun from time-of-day rotation + seasonal
  declination via `axialTilt`; key `N`), a raylib-free per-cell **insolation field**
  (`computeInsolation`, the weather hook), a **live seasonal temperature** cycling the
  static summer/winter fields over the year (`computeLiveSeason`), and a **moving snow / sea-ice
  line**. Day/night + snow are render overlays over any colour mode (3D + 2D). Save **v8** adds
  the live-clock state. Still **future:** actual weather, day/night temperature swing,
  precipitation/evaporation, living/evolving ecosystems.
- **Moons + tides + distant sun** *(done — see `PlanetOcean.cpp`)* — **1–3 moons** generated per
  world from a separate RNG (no tectonic perturbation) and **saved (v9)**; they orbit on the live
  clock and, with the sun, raise an **equilibrium tide** (`computeTides` → `sTide`, two bulges via
  `cosθ²−⅓`, semidiurnal). Tides show as a **tide-coloured coastline** (`buildCoastline` + a
  diverging `tideColor`, key `T`, 3D + 2D). The 3D **sun** is now small + far with a faint halo;
  **moons** render with sun-lit **phases** (offset-dark-sphere) + faint **orbit rings**, plus
  **eclipses** — solar (a moon transiting the sun darkens a shadow spot in the day/night overlay),
  lunar (a moon in the planet's shadow dims red). Knobs `tideAmplitude`/`tideSunFactor`.
- **Ocean currents (+ climate feedback)** *(done — see `PlanetOcean.cpp`)* — `computeOceanCurrents()`
  builds a per-ocean-cell tangent velocity from wind stress (`sWind`) + Coriolis deflection
  (right N / left S) + coast-following (gyres) + smoothing. `computeClimate()` calls it and feeds
  **warm (poleward) / cold (equatorward)** currents back into `sTemp` as a bounded coastal anomaly
  (`climateCurrentFactor`), so biomes shift naturally. Rendered as warm/cold **current arrows**
  over the sea (key `O`, 3D + 2D). This completes the Live World ocean/sky pass.
- **Weather — dynamic clouds & rain** *(done — see `PlanetWeather.cpp`)* — a per-cell
  humidity/cloud/rain cycle advanced on the live clock: **evaporate** over warm sunlit seas →
  **advect** humidity & cloud along the prevailing wind → **condense** into cloud (extra on
  windward upslopes) → **rain** out → **dissipate**. Rendered as a translucent moving cloud
  shell (white → dark storm where it rains) over the globe + 2D map (key `K`). Saved (v10).
- **Weather — moving systems (lows, hurricanes & typhoons)** *(done — see `PlanetWeather.cpp`)* —
  drifting low-pressure **agents** (`WeatherSystem`) spawn over warm tropical seas / mid-latitude
  oceans, travel with the steering wind (poleward recurve), intensify over warm water, decay over
  land, and **stamp** travelling cloud/rain onto the grid — so the sky visibly evolves. The intense
  tropical ones are **hurricanes/typhoons** (spin by hemisphere, eye + animated spiral marker).
  Saved (v11, so a load resumes active storms). This makes the weather visibly move (the base field
  alone relaxes to a static pattern).
- **Volcanoes & volcanic islands** *(done — see `PlanetVolcano.cpp`)* — on entering Live World a
  one-time pass (`placeVolcanoes`, separate RNG → tectonic determinism intact) seeds volcanoes by
  tectonic context: **very high** probability on young spreading-ridge / "new-plate" cells (baby
  plates), **medium** on normal plate borders, **low** elsewhere (hotspots). They are stateful
  lifecycle agents: some start pre-built, growing vents can breach submarine cells into volcanic
  islands, tall vents can go dormant, dormant vents explode and shave their peak, then puff ash while
  regrowing weaker. Volcano state + `sVolRng` are captured in the Live World step-back snapshot, so
  `,`/`.` reverses height, dormancy, explosions and ash timers. Rendered as growing, dormant and
  post-explosion cone markers (3D + 2D, key `V`); saved (v15). Knobs `volcano*`.

**Civilizations (in progress — the long arc after the world is finished):** the eventual goal is
people who eat, name their world, found villages→cities, build kingdoms/empires, draw cultural +
geographic borders, and go to war. Built in phases (cell = territory, settlements = point agents, all
on the Live World clock). **Steps 1–2 of the roadmap are done (plus a derived ecoregions atlas):**
- **Geography & place-names (the atlas)** *(done — see `PlanetGeography.cpp` + `NameGen.cpp`)* — the
  foundation everything civic references. `Planet::generateGeography()` extracts named features from
  the (frozen) terrain by connectivity over the fixed grid — **continents/islands** (connected land),
  **oceans** (the connected world ocean split into basins by a distance-from-land watershed → ~4–6
  named oceans) **/ seas** (small water bodies), **lakes** (inland filled basins), **mountain ranges +
  peaks** (connected high terrain), **rivers** (largest discharge mouths traced upstream via `flowTo`) — and
  names each with a deterministic procedural namer (`NameGen`: syllable banks, a "language" per
  continent so a region's places share a sound). A separate RNG (`sGeoRng`) keeps tectonic determinism
  intact. Generated once on a settled world (key `M`, in or out of Live World), drawn as labels on the
  globe + 2D map (minor features only when zoomed), listed in an **Atlas** tab (click a row to fly
  there), and shown in cell-info as a "region" line. Per-cell feature-index arrays give O(1) "which
  features is this cell in" (the hook for territory/borders later). Names dedupe on the proper-noun
  root (no two features share a base name); a **new volcanic island** is named on the fly when it
  breaches (the island-formation event carries its name). Saved (**v17**). Knobs `geo*`.
- **Ecoregions (ecological provinces)** *(done — see `PlanetEcoregions.cpp`)* — `generateEcoregions()`
  flood-fills cells sharing a biome + land/water context + productivity band into named ecological
  provinces (dominant flora/fauna/funga archetype + flora/fauna/funga productivity per region), a
  separate `sEcoRng`. Key `E` (colour mode `Ecoregion` + an **Eco** tab); saved (**v19**; v18 added a
  geography reshuffle salt). Productivity feeds settlement habitability.
- **Settlements & habitability (Step 2)** *(done — see `PlanetCiv.cpp`)* — a derived per-cell
  **habitability/food** score (`computeHabitability`: climate comfort + water access (rivers/lakes/
  coast) + food (flora/fauna density + ecoregion productivity), gated by freezing winters / high
  terrain; colour mode `Habitability`, key `I`). On key **`U`** ("the dawn") `placeSettlements()` seeds
  a fixed set **once** on the best, well-spaced (`civMinSpacingRadians`) fertile cells (separate
  `sCivRng`; named from the continent's `NameGen` bank). `stepCivilization(dtHours, liveTime)` runs each
  live frame: population moves **logistically toward a food-driven carrying capacity**, but everything is
  **environment-driven and dynamic** (not the old "grow the same everywhere"): the growth **rate** scales
  with habitability (fertile cells boom, marginal crawl); the capacity `K = civMaxPopulation·habitability·
  **siteQuality**·conditions` where **siteQuality** spreads max size by orders of magnitude (a great river
  — `discharge` is log-scaled — or a coast hosts a metropolis, a dry inland cell a town); and
  **conditions** are deterministic time-varying drivers (pure functions of (region, year, seed) → constant
  within a year, reversible on step-back): **regional droughts** (multi-year, worse in arid regions),
  year-to-year **harvests** (bigger swings in continental interiors), rare **cold years** and river
  **floods**, plus **volcano ash**. **Storms** over a town kill people directly (hurricanes worst,
  `civStormDeathRate`/`civHurricaneDeathMult`); sustained famine / acute disasters can **collapse** a
  settlement to ruins (kept in the set, can revive). Tiers village→town→city; markers (3D + 2D) sized by
  tier and **withered-tinted** by hardship + a **Civ** tab + cell-info "conditions/drought" line + kind=3
  `WorldEvent`s ("X grew into a city", "Hurricane <name> devastates X", "Famine shrinks X to a Town", "X
  was abandoned"). The set is fixed, so the step-back snapshot only restores the per-settlement
  **population** vector; conditions recompute. Saved (**v20**). Knobs `civ*`.
  *Next steps (not yet built): territory + borders, kingdoms/empires, culture + beliefs, conflict +
  diplomacy.*

## Current state

Working and verified (logic tested headless):
- Icosphere level 5 → 10242 cells, ~223 km/cell, topologically correct
  (exactly 12 degree-5 vertices, rest degree-6).
- Plate flood-fill, drift as rotation on the sphere, boundary-stress uplift.
- Relief builds *gradually* toward an isostatic equilibrium (no clamp-rail
  saturation): after ~40 ticks graded mountain belts (>2000 m) and deep
  subduction trenches (<-6000 m), 0% of cells pinned to the clamp.
- `test_logic.cpp` asserts geometry, plate assignment, non-saturation and
  graded relief; run it after any `Planet::step()` change (see below).
- raylib render: 3D globe (top) + 2D Equal Earth map (bottom strip), orbit
  camera, 4 color modes. Phase 1 is a **generator**: it paces tectonic ticks
  toward isostatic equilibrium (watchable, ~3 s), renders live, and
  **auto-pauses** once the terrain settles (max per-tick change < 2 m). No
  background thread — that's Phase-2 (continuous drift/erosion) groundwork.
- **Phase 2 increment 1 (drift):** after forming settles, the app switches to
  continuous **drift mode** on a My clock. Each plate has a real speed (1..20
  cm/yr); `cflDtMy()` sets the timestep so the fastest plate advances ~half a
  cell/step. `advect(dt)` moves plate membership + carried crust (plateId,
  elevation, oceanic, geoAge) by an accumulation scheme: a boundary cell builds
  `drift` (signed convergence distance) with its dominant other-plate neighbor;
  +1 cell -> overrun (take that crust; but oceanic can't overrun a buoyant
  continent -> it subducts under), -1 cell -> new young ridge crust (spreading).
  Crust type now lives on the **cell** (`Cell.oceanic`), not the plate. The HUD
  shows elapsed My; `[`/`]` set My/sec; auto-settle still gates Phase 1 -> 2.
- **Phase 2 increment 1.5 (plate lifecycle):** without this the count collapsed
  to 1-3 and the world froze (a giant continental plate that can't shed cells).
  Every `splitCheckEvery`(10) advect iterations (gated by `driftIter`) `advect()`
  runs a Wilson-cycle lifecycle: **fission** (a plate over `splitFraction`(20%)
  of cells splits along a random great circle through its centroid; prob ramps
  `0.05+0.05*(pct-20)`, the new half gets a random drift — self-regulating, so
  the count equilibrates ~8-12), **stalemate kick** (a plate whose size barely
  changed over a window gets a new direction + speed boost to break deadlocks),
  and **spreading plates** (rift cells become a `Plate.baby` young-ridge strip;
  `coalesceBabyPlates()` merges connected blobs and dissolves tiny noise ones;
  a strip past `babyPromoteFrac`(0.7%) is promoted to a real plate with random
  drift + `volcanicLandFrac` of its interior turned to volcanic-island land).
  The hard land clamp became a **soft band** (`landBand`) so volcanic land
  persists; `acquirePlate()` reuses dead plate slots to keep `plates` bounded.
  Stats panel separates real plates from "Young ridges: N strips"; plate-color
  mode tints baby cells a uniform ridge grey. Verified by a headless soak.
- **Phase 2 increment 1.6 (calmer + cleaner plate map):** kicks were too twitchy
  ("strange border movement") so a plate must now stall for `stalemateWindows`(4)
  consecutive check windows (`sStaleStreak`) before a kick. `deleteEnclosedPlates()`
  absorbs any plate ringed by a single other plate into it (on a mutual pair only
  the smaller). `fuseMiniPlates()` lets >= `fuseMinPlates`(3) clustered mini plates
  (non-baby, < `miniPlateCells`) fuse into the largest member and steal one ring of
  cells from their largest big neighbour (terrane amalgamation). Borders now draw
  in two colors: real plate borders yellow, young spreading-ridge borders red
  (3D + 2D, both via `B`). Soak: mini plates ~0, no enclosed slivers, ~8-12 plates.
- **Phase 2 increment 2 (erosion + sea level):** `Planet::erode(dtMy)` runs each
  drift step after advect+step — a mass-conserving, slope-weighted downhill
  sediment transport (one double-buffered gather pass): the higher cell of each
  edge gives material to the lower, faster above sea level (`erosionLandRate`)
  than below (`erosionSeaRate`). Highs wear down toward an uplift<->erosion
  equilibrium; sediment fills basins and builds coastal shelves/deltas. No river
  carving (sub-cell at 223 km -> subgrid later). `adjustSeaLevel()` (every
  `seaLevelEvery` erode calls) eases `cfg.seaLevel` toward the percentile
  elevation leaving `landFractionTarget` (30%) of cells above water — percentile
  targeting (`nth_element`) because a proportional nudge oscillates across the
  flat continental-base elevation. Two "land" notions coexist: crust type (plate
  buoyancy) vs geographic (elev > seaLevel). Stats headline + water:land are now
  geographic, with separate "Sea level" and "Crust %" lines. Headless: land -> 30%
  all seeds, erosion conserves sum(elevation), deterministic.
- **Phase 2 increment 3 (gradual sea level + config/save files):** the sea-level
  controller is now gradual — checked every `seaLevelEvery` (100) erode calls, it
  nudges sea level by a fixed `seaLevelStep` (100 m) when outside a `seaLevelTol`
  (2%) deadband, and only if the nudge reduces the error (so it rests near a flat
  "cliff" instead of oscillating). A human-editable **`planet.cfg`** (key=value)
  holds all PlanetConfig params (auto-created on first run, `F2` reloads +
  regenerates); `loadConfig`/`saveConfig` share one `CONFIG_FIELDS` X-macro. A
  **`planet.save`** binary holds seed + config + full planet state
  (`Planet::writeState`/`readState`; geometry rebuilt from subdivisions via
  `buildGeometry()`); `F5` saves, `F9` loads and resumes (deterministic
  continuation, verified headless). File I/O lives in Planet (raylib-free).
- **Phase 2 polish (config validation, QoL, sim cleanups):** `validateConfig()`
  range-checks every field (+ the cross-rule `oceanBase < continentBase`) on load
  and `F2`; an invalid `planet.cfg` reverts to safe defaults without overwriting
  it. Save bumped to **version 2** (now also persists the `[`/`]` drift rate;
  version-gated reads accept older saves). Viewer adds a **crust-type color mode**
  (`4`: continental warm brown / oceanic deep blue), `F` **fast-forward** (runs
  `step()` to settled instantly), `F12` screenshot, `--seed`/`--config` CLI flags,
  a `P<id>` label per plate on the drift arrows, and a min subdivision level of 1
  (level 0 disallowed). Two sim refinements: `step()` re-anchors boundary (source)
  cells to their original stress each dilation ring so adjacent belts don't
  cross-inflate (sharper peaks; land flank cells 509->499); and the soft land-band
  rift/accrete nudge now reads a frozen snapshot of pre-nudge `oceanic` so flipping
  one cell can't cascade along vertex-index chains into linear "snakes". The
  earlier drift-direction "inward" fix was reverted (it worsened snaking).
- **Phase 2 increment 4 (taller mountains + seafloor aging):** mountains used to
  cap ~5000 m because collisions were under-weighted and `relax` snapped uplifted
  crust back to `continentBase` once a migrating front passed. Now `step()` adds a
  real **continent-continent collision** factor (`colliding[]` = continental cell
  facing continental, `cfg.collisionFactor`) and an **Andes-class continental arc**
  factor (`cfg.arcFactor`), and high continental crust gets **isostatic
  persistence**: `relaxEff = relax*(1 - isostaticPersist*clamp((elev-continentBase)
  /rootScale,0,1))`, so thick ranges stand and become *erosion-limited* (by the
  drift-loop `erode()`) instead of relaxing away. These three boosts are **gated on
  the `Planet::drifting` flag — active only in Phase-2 drift, OFF during Phase-1
  forming** (which keeps the original mild factors + full relax). This is
  deliberate: Phase-1 forming runs `step()` with no erosion, so if the strong
  uplift + weak relax were active there it would never settle (uplift never
  balanced) and would rail the clamp — gating to drift, where `erode()` runs every
  tick, avoids both. main.cpp sets `planet.drifting=true` when forming settles (and
  in `loadGame` from the saved phase), `false` on reseed/regen. **Seafloor aging->depth:**
  oceanic crust subsides with `geoAge` via `oceanicBase(age) =
  max(oceanBase, ridgeDepth - seafloorSubsidence*sqrt(age))` (half-space cooling);
  `oceanBase` is now the **deep abyssal floor** (-6000 m), `ridgeDepth` the shallow
  young value (-2500 m), and `seedInitialRelief()` seeds an oceanic age spread
  (`seafloorSeedAge`) so the starting seafloor already has ridge->abyss variety.
  Headless: ~half of seeds produce >7000 m ranges that persist (the rest are
  legitimately low-relief ocean worlds), <2% pinned to the clamp on all seeds,
  older seafloor markedly deeper, deterministic. Tune the new knobs in `planet.cfg`.
- **Phase 3 increment 1 (hydrology: rivers, lakes, fluvial erosion):**
  `Planet::hydrology(dtMy)` = `routeFlow()` then mass-conserving fluvial erosion, on
  the fixed grid (Eulerian, raylib-free). `routeFlow()` does priority-flood
  depression-filling (epsilon tilt so flats drain; ocean cells are outlets) →
  `sFill`/`sLakeDepth` (a cell with `lakeDepth>0` above sea level is a **lake**),
  steepest-descent over the filled surface → `sFlowTo`, and flow accumulation in
  descending-fill order → `sDischarge` (rivers = `discharge>riverThreshold`). The
  erosion pass walks the network upstream→downstream carrying a sediment load:
  stream-power incision `K*Q^m*S^n*dt` where under capacity, deposition where over
  (`cap=riverTransport*Q*S`) — filling lakes, building deltas at mouths, depositing
  the remainder at ocean sinks so **sum(elevation) is conserved**. Lakes/rivers are
  **derived from elevation each tick** (no new saved per-cell field; only erosion
  writes back to `elevation`). Orchestration (main.cpp): after `phase3AfterMy`
  drift-My the sim **pauses and prompts** ("Continue Phase 2" / "Start Phase 3");
  `H` toggles Phase 3 manually. In Phase 3 the drift loop keeps running
  (advect/step/erode) but at a **finer dt** (`cflDtMy()*phase3DtScale`) plus
  `hydrology(dt)` — drift never stops, just resolves finer. Lakes shade inland-water
  blue (`recolor`); rivers draw as a `centroid→downstream` line network (3D + 2D,
  two widths, `J` toggles). Save bumped to **v3** (+ a `phase3` header flag).
  Headless: discharge grows downstream and all land rainfall reaches the sinks,
  mass conserved to ~1e-15, ~10 lake systems + rivers persist, deterministic.
  (Note: the hydrology phase is now framed in the UI as **Phase 2.5**; the
  internal `phase3*` names are unchanged.)
- **Phase 3 increment 1 (biomes — classify + color):** `Planet::classifyBiomes()`
  (src/sim/PlanetBiomes.cpp, raylib-free) writes a per-cell `Cell.biome` (enum
  `Biome`, 13 entries: Ocean, **Ice**, Lake, Beach, Wetland, Grassland, Savanna,
  Desert, Forest, Taiga, Tundra, Hills, Mountains). A first **rule-based** pass with
  no real climate yet: temperature = warm-equator curve (super-linear in latitude so
  cold concentrates at the poles) minus an elevation lapse; moisture = latitudinal
  rainfall belts (wet equator/mid-lat, dry subtropics→deserts) + river discharge +
  coastal proximity; classified first-match (ice→ocean→lake→beach→mountains→hills→
  lowland-by-temp/moisture). **Polar ice caps** fall out of the temperature test (it
  also snow-caps high peaks). All thresholds are **tunable in `planet.cfg`** (the
  `biome*` PlanetConfig fields — `biomeIceTemp`, `biomeMountainElev`, the moisture
  cutoffs, etc.; only the latitudinal rainfall-belt curve shape stays a fixed helper).
  The biome is **saved per cell** — save bumped to **v4** (per-cell biome byte appended
  after `invader`; `readState(is, hasBiome)` reads it for v4, reclassifies for v3, so v3
  saves remain loadable). Rendered as color mode `5` (`biomeColor`, src/render/Colors.cpp);
  re-run each `refreshView`. `lakeColor` changed to bright turquoise so lakes read clearly
  vs ocean (the "blue speckle" near a clicked cell is just the subgrid detail overlay,
  where ±250 m value-noise dips below sea level near coasts — not lakes). Headless:
  every cell valid, both poles Ice, deep equatorial water Ocean, ≥4 land biomes present,
  deterministic, v4 round-trips biome, v3 loads + reclassifies.
- **Phase 3 polish (smaller caps + axial tilt + grid labels):** ice caps trimmed a few
  points (~17%→~14% of cells) by lowering `ICE_TEMP` in PlanetBiomes.cpp. Added a
  planetary **`axialTilt`** (obliquity, default 23.44°, in PlanetConfig/`planet.cfg`):
  the 3D globe + a drawn **spin-axis rod** (through the poles, red/blue pole caps) lean
  by it via an `rlRotatef` about world Z wrapping all 3D content in `renderGlobe3D`;
  picking un-rotates the world hit dir by −tilt (`rotateZ`, src/render/Picking.cpp) and
  3D plate labels rotate by +tilt so everything stays consistent (the picking sphere is
  rotation-invariant). Biomes/2D map are unchanged (tilt is visual + groundwork for
  seasons). The graticule (`G`) now shows **lat/lon degree numbers on the 2D map** edges
  (`drawGraticuleLabels2D`, plain "60N"/"120W" — the default font has no `°`). `axialTilt`
  was added to PlanetConfig (`planet.cfg`). Headless: ice ~14%, biome + `axialTilt`
  round-trip, deterministic.
- **Phase 3 polish (biome knobs in config + future-proof save):** the 17 biome
  classification thresholds moved from constants into PlanetConfig `biome*` fields
  (tunable in `planet.cfg`, `F2`). To stop config additions from breaking saves each
  time, the save now stores config as a **self-describing key=value text block** (save
  **v6**) parsed like `planet.cfg` (`writeConfigFields`/`parseConfigStream` shared);
  doubles written at `precision(17)` round-trip exactly. Adding/removing config fields no
  longer breaks saves; v6 just can't load pre-v6 saves (one-time break). Headless: cfg
  (incl. non-default `biome*`) round-trips exactly, unknown/missing keys handled.
- **Phase 3 increment 2 (climate model):** `Planet::computeClimate()`
  (src/sim/PlanetClimate.cpp, raylib-free, derived/not saved) builds two continuous
  per-cell fields. **Temperature** `sTemp` (°C) = the latitude curve (`biome*` temp
  params) − elevation lapse. **Precipitation** `sPrecip`: prevailing winds are zonal by
  band (tropics/polar easterly, mid-lat westerly); ocean cells are a moisture source and
  each land cell takes its **upwind** neighbour's moisture, **rains out** more on windward
  upslopes (orographic) and loses a multiplicative fraction per cell (continentality), so
  leeward + deep-interior cells dry out. The raw field is near-binary (saturated where the
  wind hits the sea, ~0 elsewhere), so it's **diffused** `climateMoistureSmooth` passes to
  create wet→dry transition zones, then normalized to `sMoist` (0..1, **median land →
  0.5**, robust to orographic spikes). `classifyBiomes()` now reads `sTemp`/`sMoist`
  (dropping the old latitude+discharge+coast hack) → rain-shadow/interior **deserts** + a
  varied, per-world biome spread; wetlands now require adjacency to water (ocean/lake).
  Color modes `6` (temperature, blue→red) / `7` (precipitation, dry→wet). `computeClimate()`
  runs before `classifyBiomes()` in `generate()` and `refreshView()`. New `climate*` config
  knobs (planet.cfg). Headless: equator warm/poles cold, lapse, coastal wetter than interior,
  deserts present, deterministic.
- **Seasons (obliquity):** `axialTilt` (previously visual-only) now drives a per-cell seasonal
  temperature range. `computeClimate()` adds derived `sTempSummer`/`sTempWinter` (= annual mean
  `sTemp` ± a half-amplitude `A = seasonAmpMax·tiltFactor·latShape·continentality`), where
  `tiltFactor = sin(axialTilt)/sin(23.44°)` (0 tilt → no seasons) and **continentality** comes
  from a multi-source BFS ring-distance from ocean cells (coasts/oceans muted by thermal
  inertia, interiors swing most). Big swings at high-latitude continental interiors, ~0 at the
  equatorial coast. `classifyBiomes()` blends **winter** temp into the Tundra/Taiga cold cutoffs
  via `biomeSeasonWeight` (0 = annual-mean-only/old behaviour, default 0.6) so cold-winter
  interiors turn boreal/tundra (Siberia effect) — the amplitude is geographically shaped, so
  this expands cold biomes only where seasons bite. Derived/not-saved (no save bump). Color key
  `6` now **cycles** mean→summer→winter→seasonality; cell-info shows summer/winter. New `season*`
  + `biomeSeasonWeight` config knobs. Headless: equator swing ≈1.6 °C vs ≈20 °C at high latitude,
  interior land ≫ ocean, tilt=0 → no seasons, higher tilt → bigger swing, `biomeSeasonWeight=0`
  leaves biomes unchanged, cold-biome count rises with seasons, deterministic.
- **UI polish (full cell info + view label + framing):** the cell-info panel
  (`cellInfo`, src/render/Panels.cpp) now shows everything per cell — crust type, **biome**
  (`biomeName`), **temperature** + **precipitation %**, and **river/lake** when hydrology is
  on — in addition to the existing cell#, lat/lon, elevation, plate, geoAge. The active
  color mode is shown **top-center** of the globe ("Biome view", etc., via `colorModeName`),
  updating with `1`–`7`. The HUD title/status and the hydrology prompt were reworded to drop
  the rigid "Phase N" labels (now "World Creation: forming / drift & erosion / hydrology");
  internal `phase*` names are unchanged. Render/text only — no sim/save/config change.
- **Biota (flora/fauna/funga):** the World-Creation stage after biomes. Two layers (src/sim,
  raylib-free): (1) **density scalars** `sFloraDensity`/`sFaunaDensity`/`sFungaDensity` ∈ [0,1]
  via `Planet::computeBiotaDensity()` — flora = NPP Liebig-min of temp & moisture (0 on
  water/Ice), fauna = herbivore capacity ∝ flora with carnivores gated on local prey
  (`bioCarnPreyMin`), funga = flora-like but moisture/organic-matter-led + cold-tolerant.
  Derived each tick (like climate), drive color modes `8`/`9`/`0`. (2) A discrete
  **slot/point population** `Planet::generateBiota()` (key `L`, on a settled world) — each land
  cell draws broad **archetypes** from a comprehensive table (`biotaArchetypes()`, 49 entries
  across Flora/Fauna/Funga incl. marine, each with Class/Order/Family/Size + a biome mask + climate
  tolerance) into a per-kind slot cap + a density-scaled point budget (Tiny=1…Huge=5 cost),
  weighted by suitability and a **regional bonus** for archetypes already placed in same-biome
  neighbours (homogeneous regions, variety at boundaries). Organisms are labelled by their
  **taxonomy** — Family + Size + role (e.g. *Felidae (Big, Carnivore)*, with the full
  *Class > Order > Family* tree in `organismTaxonomy()`), never an informal common name like
  "big cat"; generalist families get a biome adjective (*Desert Muridae*). Uses a **separate
  RNG** seeded from `cfg.seed` so generating biota never
  perturbs tectonic determinism. Population is **saved** (`sBiota`, save **v7**); densities are
  derived/not-saved. New files `PlanetBiota.{hpp,cpp}` + `PlanetFlora/Fauna/FungiGen.cpp`;
  color modes `floraColor`/`faunaColor`/`fungaColor`; cell-info shows density % + the per-kind
  organism list. `bio*` config knobs. Headless `test_biota.cpp`: density ranges/zeros, fauna≤
  capacity, carnivore gating, slot/point budgets, determinism + RNG isolation, v7 round-trip,
  pre-v7 loads empty. v7 reads v6-and-older (no biota block → empty population; press `L`).
- **Biota — marine flora & fauna (life in the ocean):** the biota layers used to be 0 on every
  water cell (a hard `elevation<=sea` gate + no Ocean-masked archetypes), so the sea read as
  barren. Now ocean cells (not under polar `Ice`) get a **marine primary productivity** in
  `computeFloraDensity`: `base + (1-base)·max(shelf, coast)` where `shelf` = shallowness
  (`1 - depth/bioMarineShelfDepth`, light to the photic floor) and `coast` = a multi-source BFS
  **ring-distance from land** (nutrient runoff; mirrors the continentality BFS, seeded from land
  not ocean) — so productivity is rich on sunlit shelves/coasts, lower in the deep open ocean,
  zero only under ice; `sMoist` (a *land* rainfall field) is **not** used at sea. `computeFaunaDensity`
  now skips only `Ice` (was all water) so marine fauna = `flora·productivity`, with the existing
  carnivore prey-gate clustering sharks/seals/squid on rich shelves. **Funga stays land-only.**
  `generateBiota` populates ocean cells too (skip `Ice`; no marine funga) — `fillFlora`/`fillFauna`
  are unchanged because their biome-mask filter draws only the **new Ocean-masked archetypes**
  appended to `biotaArchetypes()`: marine flora **Kelp / Seagrass / Phytoplankton** and marine fauna
  **Forage fish / Reef fish / Shark / Baleen whale / Seal / Squid** (all `moistMin=0`, SST-zoned;
  append-only so v7 saves are unaffected — old saves just lack them until `L`). The flora/fauna
  color views (`8`/`9`) render ocean on a **distinct marine ramp** (`marineFloraColor` deep
  blue→teal/green bloom, `marineFaunaColor` deep blue→cyan→warm) so the sea still reads as sea;
  land ramps + the funga view unchanged. New `bioMarineBase`/`bioMarineShelfDepth`/
  `bioMarineCoastRings` config knobs (self-describing config → **no save bump**). `test_biota.cpp`
  updated: zero life under ice, marine flora/fauna present at sea + populate ocean tiles, funga 0
  on water, capacity/carnivore-gate/budgets/determinism still hold.
- **Live World — clock + day/night + live seasons + snow line:** the first **Live World** stage
  (the slow real-time arc after World Creation). Engine (`src/sim/PlanetLive.cpp`, raylib-free,
  derived/not-saved): `computeInsolation(dayOfYear01, timeOfDay01)` → `sInsolation` (0..1 cosine
  solar incidence; declination `axialTilt·sin(2π·doy)`, sub-solar longitude sweeps once per day;
  the foundation the future weather sim reads) and `computeLiveSeason(doy)` → `sLiveTemp` (the
  annual-mean `sTemp` swung toward the existing `summerTemp`/`winterTemp` by the seasonal phase,
  anti-phased across hemispheres). Viewer: key `W` (settled world) toggles **Live World** — drift
  freezes and `liveTime` advances at `liveRate` (sim hours/real-second), `[`/`]` ramp it
  hour→month; the HUD shows a `Year/Day/HH:MM` calendar (`dayLengthHours`/`yearLengthDays`).
  `rebuildLiveOverlay()` builds a per-cell day/night brightness (`illum`, soft terminator, dim
  night floor) + `shadedColors` (base colour → snow on cold land / sea-ice on cold ocean via
  `snowTemp`/`seaIceTemp` → day/night dim); both the 3D globe and 2D map draw `displayColors()`
  (the overlay over **any** colour mode), `N` toggles the terminator, a sun marker sits over the
  lit hemisphere. Cell-info adds a `live temp / day-night / snow` line. Save **v8** appends the
  Live World flag + `liveTime` (version-gated; older saves load with it off). New `PlanetLive.cpp`
  in CMake + the headless list; `test_live.cpp`: insolation range, lit/dark hemispheres,
  declination tracks `axialTilt` (polar day/night at solstice), live temp within the
  summer/winter band + anti-phased, snow line advances in winter, determinism.
- **Live World — moons, tides & a distant sun:** engine `src/sim/PlanetOcean.cpp` (raylib-free):
  `generateMoons()` seeds **1–3 moons** (`Moon` struct in PlanetTypes) from a separate RNG
  (`cfg.seed ^ 0x900D5EED`, tectonic stream untouched); `sunDirection`/`moonDirection`/
  `moonOrbitNormal` give model-space sky geometry (one source of truth — `computeInsolation` now
  calls `sunDirection`). `computeTides(doy,tod,days)` → `sTide` (m), equilibrium two-bulge tide
  (`Σ w·(cosθ²−⅓)`, moons + sun weighted `tideSunFactor`, scaled `tideAmplitude`); derived/not
  saved. Viewer: `T` colours the **coastline** (`buildCoastline` dual-contour + `tideColor`
  diverging amber↔cyan, per-segment in 3D + `drawColoredSegments2D` in 2D), auto-scaled to the
  tide extent; `stepSim` computes tides + `moonDirs`/`moonNormals` each live frame. 3D render:
  small **distant sun** (`sunDist`≈9) + halo; **moons** at a visible orbit band with sun-lit
  **phase** (offset-dark-sphere), faint **orbit rings**, and **eclipses** — solar shadow folded
  into `rebuildLiveOverlay`'s `illum` near the sub-solar point, lunar dimming (reddish) when a
  moon is in the planet's shadow. Cell-info adds a tide line; stats shows the moon count. **Save
  v9** appends the moons block (`writeState`/`readState(...,hasMoons)`; pre-v9 saves synthesize
  moons from the seed). `test_ocean.cpp`: moon count/determinism + RNG isolation, unit sweeping
  sky dirs, zero-mean two-bulge tide (high under moon + antipode, low at 90°, moves with time),
  save v9 round-trip. **Enclosed-sea cap:** `computeTides` flood-fills connected ocean bodies and
  caps the amplitude of any body under 10 cells to `0.01·cells + 0.03` m (a one-cell sea ≈ 0.04 m,
  an inland saltwater lake stays calm) — a small closed basin can't build a real tidal range;
  open oceans (≥10 cells) keep the full equilibrium tide.
- **Live World — ocean currents + climate feedback:** `Planet::computeOceanCurrents()`
  (PlanetOcean.cpp) builds a per-ocean-cell tangent velocity `sCurrent` (derived/not saved):
  wind stress (`sWind`) rotated by a **Coriolis** deflection (right N / left S about the cell
  normal), the across-shore component removed at land neighbours so flow **follows coasts**
  (gyres), then 3 smoothing passes (re-projected to the tangent plane; zero on land).
  `computeClimate()` calls it right after the wind pass and feeds it back: a **bounded coastal
  temperature anomaly** = `climateCurrentFactor · (poleward speed / max)` on ocean cells (warm
  poleward, cold equatorward), smoothed onto the coasts and added to `sTemp` **before** seasons,
  so summer/winter + biomes shift with it. Render: `buildCurrents` emits subsampled warm/cold
  **arrows** over the sea (warm = poleward/red, cold = equatorward/blue), key `O` (3D + 2D), built
  in `refreshView`. New knob `climateCurrentFactor` (4 °C). `test_ocean.cpp` adds: currents
  tangent + zero on land + widespread, feedback bounded by the knob and produces both warming and
  cooling, deterministic. Live-World ocean/sky pass complete.
- **Live World — dynamic weather (clouds & rain):** `Planet::stepWeather(dtHours)`
  (PlanetWeather.cpp) advances a per-cell humidity/cloud/rain cycle on the live clock:
  **evaporate** over warm sunlit ocean (uses `sInsolation`+`sTemp`), **advect** humidity & cloud
  downwind (upwind differencing along `sWind`/`sUpwind`, `weatherWindKmh`), **condense** the
  supersaturated air into cloud — saturation `weatherSatBase + weatherSatTempCoef·T`, plus
  windward **orographic** lift — **rain** out cloud above `weatherRainThresh`, then **dissipate**.
  `initWeather()` spins the fields up from the moisture climatology; bounded exponential rate
  forms keep it stable at any timestep. Runs each live frame in `stepSim` (dt = the same sim-hours
  added to `liveTime`; held when paused). Render: a translucent **cloud shell** (white → dark
  storm where it rains, alpha = cover) over the 3D globe + a `drawWeather2D` layer on the 2D map,
  key `K` (default on); cell-info adds cloud/humidity/raining. **Saved v10** (humidity/cloud/rain,
  flag-gated; older saves spin weather up live). Deterministic (no RNG). `test_weather.cpp`:
  fields in range, clouds form + rain falls, oceans moister than land, determinism, v10 round-trip.
- **Live World — moving weather systems (lows / hurricanes / typhoons):** the base cloud/rain
  field relaxes to a *static* pattern under fixed forcing, so `stepWeather` now also runs a
  population of drifting **`WeatherSystem`** agents (PlanetTypes; **saved v11**; separate
  `sWeatherRng` seeded from `cfg.seed` → tectonic determinism intact). Each step: **spawn** over
  warm tropical ocean (5–25°, SST ≥ `weatherTropicalSST`) or a mid-latitude (30–62°) ocean low
  (capped at `weatherSystemMax`, prob ∝ `weatherSpawnRate`); **move** along the steering wind
  (`sWind` at the nearest cell) + a poleward recurve at `weatherSystemSpeed`; **intensify** over
  warm sea / **decay+cull** over land/cold; **stamp** a Gaussian cloud/rain shield
  (`weatherSystemCloud`/`Rain`, scaled by strength × local humidity) — so cloud clusters travel
  and dissipate behind the system. A tropical system past `weatherHurricaneStr` is a
  hurricane/typhoon. Render: an animated cyclonic **spiral marker** per system (red + eye for
  cyclones, blue lows; spins with `liveTime`·hemisphere) in 3D + 2D, HUD system/cyclone counts,
  and a storm list (basin-named) in the Live info `Weather` tab — all under `K`. `test_weather.cpp`
  adds: systems spawn, move between steps, thicken cloud, RNG isolation, determinism.
- **Live World viewer controls — storm follow-cam, 2D map zoom, clock stepper:** (1) **`Y`** cycles
  the 3D camera to **follow a storm** (by descending strength, off after the last). Tracked by a
  stable `WeatherSystem.id` (assigned at spawn from `sStormNextId`; transient, not RNG); each frame
  `handleInput` points the camera straight at it via `camYaw/camPitch` from `rotateZ(pos,+axialTilt)`
  (model→world), orbit-drag disabled while following, auto-release if it dissipates. (2) **2D map
  zoom**: `mapZoom`/`mapPanX`/`mapPanY` + `Viewer::mapViewRect()` (mapRect scaled about its centre +
  pan); every map projection call routes through it while the **scissor/frame stay `mapRect`**
  (`drawMapTris` now derives y from the rect, not the fixed `m.pos`). Mouse-wheel over the map zooms
  toward the cursor (1–8×); drag pans when zoomed, else rotates `mapLon`; 2D picking inverts the same
  rect. (3) **Clock stepper**: the `stepSim` live body is factored into `Viewer::liveAdvance(dtClock,
  dtWeather)`; **`.`** steps forward and **`,`** back by `liveRate` hours (both auto-pause, like a
  video frame-step). Weather is an integrated path (not analytically reversible), so a forward step
  snapshots the full state — `Planet::captureWeather()`/`restoreWeather()` (humidity/cloud/rain/
  storms/RNG) into a bounded `wxUndo` ring — and **`,` restores the previous snapshot**, so the
  step really reverses *everything* (clouds, rain, **moving storms**) plus the deterministic sky.
  A manual step **always** records (rate-independent, via `wxPushSnapshot`); a continuous run records
  a throttled snapshot (~1/sec) so a run is rewindable too. `,` searches the ring by time, the ring
  drops oldest past `wxUndoMax`. The most recent `wxSaveMax`(40) frames are **persisted in the save
  (v12)** so a load can rewind storms past the saved moment; a load also drops any stale pre-load
  history. With no recorded past (e.g. immediately after a pre-v12 load) `,` rewinds the sky only and
  says so. `S` in Live World aliases the forward step.
- **Live World event log:** `liveInfoRect` is a tabbed panel (`Sky`, `Tides`, `Weather`, `Events`).
  The viewer-owned event journal is saved in v16, capped to the newest 200 entries, and records storm
  formation/intensification plus volcano dormancy, eruptions and island breaches. Clicking an event
  selects its cell, releases storm follow-cam, rotates the 3D view to it, and centres the 2D map at
  the current zoom.
- Mouse hover (in either view) shows per-cell info. Clicking a tile opens a
  right-side detail panel: tile info header + the tile's subgrid drawn as a
  flat hoverable grid of subtiles (neighbor-owned subtiles dimmed). A high-res
  subgrid patch is also overlaid on the globe for context; the hovered subtile
  is marked on the globe. `C` closes the panel.

## Architecture

The code is split into a **raylib-free engine** (`src/sim`, testable headless)
and a **raylib viewer** (`src/render`); `src/main.cpp` is a ~10-line entry point.
`Planet` is one class implemented across several `.cpp` files (one per phase/
concern, all sharing `Planet.hpp`); the viewer is one `Viewer` struct whose state
+ methods are likewise spread across a few render files. CMake adds both folders
to the include path, so includes stay flat (`#include "Planet.hpp"`, `"Viewer.hpp"`).

```
src/
  main.cpp          entry point: build Viewer, init(argc,argv), run()
  sim/   (raylib-free engine -- testable headless)
    Vec3.hpp          double-precision 3D vector math
    IcoSphere.*       geodesic icosphere: fixed vertices + neighbor adjacency
    Projection.hpp    Equal Earth equal-area projection (forward + Newton inverse),
                      dir<->lon/lat helpers. Header-only, raylib-free, testable.
    PlanetTypes.hpp   Cell / Plate / SubGrid / PlanetConfig data structures
    Planet.hpp        the Planet class declaration + config-file func decls
    Planet.cpp        generation, geometry, plate seeding, shared helpers, subgrid
    PlanetTectonics.cpp  step() (Phase 1/2 stress->uplift->relax)
    PlanetDrift.cpp      cflDtMy/advect + plate lifecycle (fission/kick/baby/fuse)
    PlanetErosion.cpp    erode() + adjustSeaLevel()
    PlanetHydrology.cpp  routeFlow/computeHydrology/hydrology (Phase 3)
    PlanetClimate.cpp    computeClimate() (temperature + orographic precipitation)
    PlanetLive.cpp       computeInsolation/computeLiveSeason (Live World: day/night + live seasons)
    PlanetOcean.cpp      moons (generate/orbit) + computeTides + computeOceanCurrents
    PlanetWeather.cpp    stepWeather (Live World dynamic clouds & rain cycle)
    PlanetVolcano.cpp    placeVolcanoes/stepVolcanoes (Live World volcanoes + islands)
    PlanetBiomes.cpp     classifyBiomes() (per-cell Cell.biome from elev + climate)
    PlanetBiota.hpp      BiotaKind/SizeClass/EcoRole/Organism/CellBiota + archetype table decls
    PlanetBiota.cpp      archetype library + slot/point draw + generateBiota/computeBiotaDensity
    PlanetFloraGen.cpp   computeFloraDensity + fillFlora
    PlanetFaunaGen.cpp   computeFaunaDensity + fillFauna (carnivores gated on prey)
    PlanetFungiGen.cpp   computeFungaDensity + fillFunga (moisture/organic-matter rule)
    NameGen.*            deterministic procedural name generator (syllable banks; reused by civ arc)
    PlanetGeography.*    generateGeography() (named features: continents/oceans/ranges/rivers/lakes)
    PlanetEcoregions.*   generateEcoregions() (named ecological provinces + dominant biota/productivity)
    PlanetCiv.*          computeHabitability/placeSettlements/stepCivilization (settlements; civ Step 2)
    PlanetIO.cpp         config file (text) + binary save/load
  render/  (raylib viewer)
    Colors.*          cell color modes (elevation/plate/age/crust/biome/climate/biota)
    Map2D.*           Equal Earth 2D map: positions + projection/draw helpers
    Overlays.*        borders, drift arrows, rivers, graticule, segments, subgrids
    Picking.*         mouse ray / sphere hit / nearest-cell / angle helpers
    Panels.*          right-column UI: detail panel, hover info, world stats
    Viewer.{hpp,cpp}  Viewer struct: all state + setup + sim orchestration
    ViewerInput.cpp   handleInput(): camera, hover picking, click, keys
    ViewerRender.cpp  renderGlobe3D / renderMap2D / renderPanels / renderHUD / renderPrompt
CMakeLists.txt    fetches raylib 5.5 via FetchContent; lists src/sim + src/render
BUILD.md          dependencies + build/run + controls
```

### Key data structures (src/sim/PlanetTypes.hpp)

- `Cell` — `unit` (fixed sphere direction), `elevation` (continuous meters,
  double, NOT quantized), `plateId`, `geoAge`, `neighbors`, and a
  `std::shared_ptr<SubGrid> subgrid` HOOK (still null on the cell; the viewer
  builds subgrids on demand via `Planet::makeSubGrid(cell,res)`).
- `SubGrid`/`SubCell` — a res*res patch around one macro cell; elevation is an
  inverse-distance blend of that cell + neighbors plus value-noise detail, and
  each subcell records `nearestMacro`. Phase-4 preview, generated on click.
- `Plate` — `type` (Oceanic/Continental), `driftAxis`, `driftSpeed`.
- `PlanetConfig` — `radius` (default 6.371e6 m, Earth), `subdivisions`,
  `seaLevel`, `plateCount`, `seed`.

### Resolution notes (important, was discussed in design)

- **Lateral** resolution = cell spacing = `sqrt(4*pi*R^2 / N)`. Coarse on
  purpose (~223 km at level 5). Only mountain-range scale, not single hills.
- **Vertical** (elevation) resolution is effectively unlimited: it is a
  `double` in meters. 100 m steps or finer are free. Mount-Everest /
  Mariana-Trench range is exactly representable.
- Climate (phase 3) reads elevation as a smooth continuous function, so no
  resolution is lost by coarse height bands.
- For dense detail later (population/culture), generate a per-cell **subgrid**
  on demand and mark which edge sub-cells border which neighbor macro-cell,
  so cross-boundary interaction (rain shadow, transition zones) works.

## Build & run

```bash
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/planetsim
```

Target OS is Nobara Linux (KDE/Wayland, Intel Arc A770). Dependency install
line is in BUILD.md (`dnf install cmake gcc-c++ mesa-libGL-devel ...`).
raylib 5.5 is fetched automatically — do not vendor it.

### Quick headless logic test (no display needed)

```bash
g++ -std=c++17 -O2 -Isrc/sim test_logic.cpp src/sim/IcoSphere.cpp \
    src/sim/Planet.cpp src/sim/PlanetTectonics.cpp src/sim/PlanetDrift.cpp \
    src/sim/PlanetErosion.cpp src/sim/PlanetHydrology.cpp \
    src/sim/PlanetBiomes.cpp src/sim/PlanetClimate.cpp src/sim/PlanetLive.cpp \
    src/sim/PlanetOcean.cpp src/sim/PlanetWeather.cpp src/sim/PlanetVolcano.cpp \
    src/sim/PlanetBiota.cpp \
    src/sim/PlanetFloraGen.cpp src/sim/PlanetFaunaGen.cpp src/sim/PlanetFungiGen.cpp \
    src/sim/NameGen.cpp src/sim/PlanetGeography.cpp src/sim/PlanetEcoregions.cpp src/sim/PlanetCiv.cpp \
    src/sim/PlanetIO.cpp -o /tmp/t && /tmp/t
```
(Swap `test_logic.cpp` for `test_biota.cpp`, `test_live.cpp`, `test_ocean.cpp`,
`test_weather.cpp`, `test_volcano.cpp`, `test_geography.cpp`, `test_ecoregions.cpp` or `test_civ.cpp`
to run the Biota / Live World / Ocean / Weather / Volcano / Geography / Ecoregions / Civilization
suites — same source list. CMake also builds `test_events` for the
viewer event journal.)

Use this to verify tectonics after changing `Planet::step()` without launching
the window (the engine lives in `src/sim` and is raylib-free, so it links without
any render code). The `#pragma omp` lines in `step()` are ignored without
`-fopenmp`, so this serial build is correct; add `-fopenmp` to benchmark the
threaded path.

### Performance / parallelism

`Planet::step()` is data-parallel: each pass writes only its own cell index
(double-buffered where it reads a field it writes), so the OpenMP `parallel for`
loops are **bit-identical for any thread count** (determinism intact). It is
memory-bandwidth-bound, so the speedup tops out ~3x (sub-7: ~5.1 -> ~1.5 ms)
around 4-8 threads regardless of core count. `step()` also reuses persistent
scratch buffers (the `s*` members) so it allocates nothing per tick. Small grids
stay serial via `if(n > 20000)`. Control threads with `OMP_NUM_THREADS` (4-8 is the sweet spot;
the default uses all cores for no extra gain). OpenMP is optional and
auto-detected by CMake. For a bigger leap (or 1M+ cells) the next step is a GPU
compute-shader port -- a Phase-2 effort.

## Controls

LMB drag orbit · wheel zoom · hover for cell info (3D or map) ·
click a tile to open its detail panel (subtiles) · `C` close panel ·
drag the 2D map to pan it east/west · `1`..`0` color by
elevation/plate/age/crust-type/biome/temperature/precipitation/flora/fauna/funga
(`8`/`9`/`0` = biota density; `6` **cycles** temperature → summer → winter → seasonality;
active mode shown top-center of the globe) ·
`B` plate borders · `D` drift vectors · `G` lat/lon grid · `J` rivers (Phase 3,
all in 3D + 2D) · `N` day/night terminator (Live World) · `T` tide-coloured coastline (Live World) ·
`O` ocean-current arrows (warm/cold) · `K` weather clouds/rain (Live World) ·
`V` volcano markers (Live World) · `M` place-name labels (the atlas; names the world on first use) ·
`E` ecoregions colour view (names ecology on first use) · `I` habitability heat map ·
`U` settlements (the dawn of civilization on first press; toggles markers after) ·
`SPACE` or on-screen button pause ·
`[`/`]` drift speed (My/sec) — in **Live World** the live-clock rate (hours/sec, hour→month) ·
`S` single tick (in **Live World** steps the clock forward) · `.`/`,` step the live clock
forward/back by one rate-unit (auto-pauses; `,` steps **everything** back incl. weather/storms via
an undo history) ·
`Y` cycle the 3D camera to **follow a storm** (off after the last) · mouse-wheel **over the 2D map**
zooms toward the cursor (drag pans when zoomed) · `F` fast-forward Phase-1 forming to settled ·
`H` toggle Phase 3 (hydrology) · `L` generate biota population (flora/fauna/funga,
on a settled world; re-press regenerates) · `W` enter/leave **Live World** (settled world) ·
`R` reseed ·
`+`/`-` subdivision level (1..7) · `F5` save (`planet.save`) · `F9` load ·
`F12` screenshot (`screenshot.png`) · `F2` reload `planet.cfg` + regenerate.

Phase 3: after `phase3AfterMy` simulated years a modal prompt asks **Continue
Phase 2** / **Start Phase 3**; `H` starts/stops it manually. In Phase 3 drift
keeps running at a finer timestep (`cflDtMy()*phase3DtScale`) while rivers, lakes
and fluvial erosion evolve.

Live World (`W`, on a settled world): geological drift freezes and a slow real-time clock runs
(`liveTime` in hours, `liveRate` = sim hours/real-second, ramped hour→month with `[`/`]`). A
moving day/night terminator (`N`), a live seasonal temperature cycle and a moving snow/sea-ice
line animate over whatever colour mode is active; the HUD shows a `Year/Day/HH:MM` calendar.
**1–3 moons** orbit (sun-lit phases, orbit rings, solar/lunar eclipses) and, with the distant
sun, raise tides — `T` colours the coastline by the live tide level (amber low ↔ cyan high).
`K` shows moving weather (clouds, rain, drifting storms / hurricanes). **Volcanoes** are placed by
tectonic context on entry and run a stateful lifecycle — submarine ones can build into new
**volcanic islands**; `V` toggles the cone/eruption markers. `Y` makes the 3D camera **follow a storm** (cycles by strength,
off after the last); `.`/`,` step the clock forward/back by one rate-unit (back rewinds the sky **and**
weather/storms/volcano lifecycle via snapshots). Mouse-wheel over the 2D map zooms (drag pans).

CLI: `--seed N` overrides `cfg.seed`; `--config PATH` uses an alternate config
file (both applied before the initial load/generate).

Two files in the working dir: `planet.cfg` (human-editable key=value of every
PlanetConfig param, auto-created on first run, reload with `F2`) and
`planet.save` (binary: seed + config + full planet state, written/read by
`Planet::writeState`/`readState`, resumes deterministically). Config is
range-checked by `validateConfig()` on load/`F2`; an invalid file reverts to safe
defaults (without overwriting your `planet.cfg`) and shows a status message. The
save header is versioned (currently **20**; v2 adds the `[`/`]` drift rate, v3 a
`phase3` flag, v4 a per-cell biome byte, v6 stores config as a **self-describing
key=value text block** instead of a raw POD dump, v7 appends the **biota population**
block — three Organism lists per cell, gated by a flag byte, v8 appends the **Live World**
clock — a flag byte + `liveTime`, v9 appends the **moons** block, v10 appends the **weather** block —
humidity/cloud/rain, flag-gated, v11 also persists the **weather systems** + RNG so a load resumes
active storms, v12 appends the most recent **step-back frames** — `wxSaveMax`(40) weather snapshots
— so a load can rewind storms past the saved moment, v13 appends the Live World clock rate, v14
appends the old pure-function **volcanoes** block, v15 replaces it with stateful volcano lifecycle
agents plus volcano state in step-back frames, v16 appends the saved **event journal**, v17
appends the **geography/atlas** block — named features + per-cell region indices, v18 a geography
reshuffle salt, v19 the **ecoregions** block, and v20 the **civilization settlements** block (the
fixed settlement set + per-frame populations in the step-back history);
newer-than-supported is
rejected. Older saves (no biota block) load fine with an empty population (press `L`);
pre-v8 saves load with Live World off; pre-v9 saves synthesize moons from the seed; pre-v10
saves spin weather up live; pre-v11 saves load with no active storms (they respawn); pre-v12 saves
load with no step-back history (you can still step forward then back); pre-v13 saves resume with
the default live clock rate; pre-v14 saves load with no volcanoes (placed on the next Live World
entry); v14 volcanoes are discarded and reseeded as v15 lifecycle agents, with old history skipped;
pre-v16 saves load with an empty event journal; pre-v17 saves load with no geography (regenerated on
demand via `M`); pre-v19 saves load with no ecoregions (regenerated via `E`); pre-v20 saves load with
no settlements (re-seeded via `U`).
A load drops any **stale** pre-load `wxUndo` history and reloads the
saved one.
**As of v6, adding/removing PlanetConfig fields no longer breaks saves** — the saved
config is parsed like `planet.cfg` (unknown keys ignored, missing keys keep defaults),
written at `precision(17)` so doubles round-trip exactly. (v6 cannot load pre-v6 saves —
a one-time break; a length guard makes that fail gracefully.) `writeConfigFields`/
`parseConfigStream` in PlanetIO.cpp are shared by `planet.cfg` and the save.

Layout (1920x1080): left column 70% wide = 3D globe (top, 60% h, RenderTexture
1344x648) + 2D Equal Earth map (bottom, 40% h, **left-aligned**, with the freed space at
its right holding the Live-World tabbed info panel — `liveInfoRect`, `renderLiveInfo`:
Sky moon phase discs, selected coastal-tile tide phase, active weather systems, and the clickable
saved event journal); right column 30% wide = cell
info (top 50% h) + subareas (bottom 50% h). 3D hover uses a custom camera ray with the
3D viewport (1344x648 at the origin -- GetScreenToWorldRay assumes the full
screen, wrong here); 2D hover uses EqualEarth::inverse (minus the `mapLon` pan).
Borders (`B`), drift vectors (`D`) and a lat/lon graticule (`G`) draw in BOTH the
3D globe and the 2D map; drag the 2D map left/right to pan longitude (`mapLon`).
The graticule (`G`) also draws **lat/lon degree numbers along the 2D map edges**. The
3D globe (and its spin-axis rod) lean by `cfg.axialTilt` (an `rlRotatef` about world Z
around all 3D content in `renderGlobe3D`); 3D picking un-rotates the world hit dir by
−tilt and plate labels rotate by +tilt (`rotateZ`, src/render/Picking.cpp) to stay in sync.
Borders draw in two colors: real plate boundaries yellow, young spreading-ridge
(baby-plate) boundaries red — both via `buildBorders` filling two segment lists.

Drift arrows: one cyan arrow per plate at its centroid along the local drift
velocity `omega x r`; length scales with speed. Rebuilt per world-gen. Each plate
is also tagged with a `P<id>` label drawn just above its centroid — projected by
hand in 3D (the project's own `Vec3` camera-basis math, matching `BeginMode3D`'s
fovy/aspect, behind-camera points skipped) and via Equal Earth in the 2D map.

**Sim model (`Viewer::stepSim`, src/render/Viewer.cpp):** single-threaded. Each
frame (while not paused/settled)
it advances ~`formRate` (55) ticks/second of `planet.step()` (Phase 1 = pure
tectonic forming, no erosion — `planet.drifting` is false) and rebuilds the view
live, so you watch the terrain rise. `step()` returns the max per-tick
elevation change; after `settleNeed` (3) consecutive ticks below `settleThresh`
(2 m) it sets `settled` and stops stepping — no idle CPU. Re-evolve / reseed /
subdivision-change clear `settled` and restart the forming pass. Rendering reads
the live `cells` directly (safe: nothing else mutates them). Phase 2's
*continuous* sim will want a worker thread + a render snapshot (so the 60 fps
render never races the sim) — that's the natural place to reintroduce threading.
Plate borders are traced once per world-gen as a dual contour through boundary
triangles (plates are fixed in phase 1).

## Tuning knobs (expect to adjust these first)

- `elevExagg` (src/render/Viewer.hpp) — visual elevation exaggeration; without it the
  sphere looks smooth.
- `axialTilt` (PlanetConfig, `planet.cfg`) — obliquity in degrees (default 23.44). Leans
  the 3D globe + spin-axis rod; groundwork for seasons. Editable + `F2` to apply.
- Biome thresholds (`biome*` in PlanetConfig / `planet.cfg`) — `biomeIceTemp` (lower =
  smaller polar/snow caps), `biomeMountainElev`/`biomeHillsElev`, the moisture cutoffs
  (`biomeDesertMoist`/`biomeGrassMoist`/`biomeWetlandMoist`), and the temperature model
  (`biomeEquatorTemp`/`biomePoleDrop`/`biomeLatExp`/`biomeElevLapse`, shared with climate).
  Editable + `F2`.
- Climate (`climate*` in PlanetConfig / `planet.cfg`) — precipitation model:
  `climateOrographic` (windward-rain strength), `climateRainEfficiency`,
  `climateContinentality` (inland drying), `climateMoistureSmooth` (diffusion passes →
  wet/dry transition zones; raise for smoother, more grassland/forest), `climateOceanMoisture`,
  `climateOroRefHeight`, `climateWindPasses`. Temperature uses the `biome*` temp params.
  `climateCurrentFactor` (4 °C) is the max coastal warming/cooling from ocean currents (0 = off;
  ocean-current arrows toggle with `O`). Current deflection angle + smoothing passes are
  constants in `computeOceanCurrents()` (PlanetOcean.cpp), not config.
- **Weather (`weather*` in PlanetConfig / `planet.cfg`):** the Live World clouds/rain cycle —
  `weatherEvapRate` (ocean evaporation speed), `weatherWindKmh` (advection speed of humidity/cloud),
  `weatherSatBase`/`weatherSatTempCoef` (how much moisture the air holds vs temperature — lower
  base = cloudier), `weatherCondense` (supersaturation→cloud rate), `weatherOrographic` (windward
  rain on mountains), `weatherRainThresh`/`weatherRainRate` (when/how fast thick cloud rains),
  `weatherCloudDissip` (cloud clearing). Toggle the overlay with `K`. Cloud render colours
  (white→storm, alpha) are constants in ViewerRender/Map2D.
- **Weather systems (`weather*` storm knobs, `planet.cfg`):** `weatherSystemMax` (concurrent
  cap), `weatherSpawnRate` (genesis frequency), `weatherSystemSpeed` (km/h drift),
  `weatherTropicalSST` (min SST for tropical genesis), `weatherSystemRadius` (cloud-shield size),
  `weatherSystemCloud`/`weatherSystemRain` (stamp strength), `weatherHurricaneStr` (strength to
  count as a hurricane/typhoon). Markers show under `K`. Tune these for a stormier or calmer world.
- Seasons (`season*` + `axialTilt` + `biomeSeasonWeight`, `planet.cfg`) — `axialTilt` is the
  master driver (0 = no seasons); `seasonAmpMax` (18 °C max seasonal half-range at full
  tilt/lat/interior), `seasonLatExp` (1.2, push swing toward poles), `seasonContinentRings`
  (6, ocean-distance to full continentality; lower = coasts go continental sooner),
  `seasonOceanFactor` (0.15, ocean/coast swing floor). `biomeSeasonWeight` (0.6) sets how much
  winter temp drives the Tundra/Taiga cutoffs (0 = annual-mean only, restores pre-seasons biomes).
- Biota (`bio*` in PlanetConfig / `planet.cfg`) — density: `bioVegTempMin`/`bioVegTempOpt`/
  `bioVegMoistRef` (flora temp/moisture limits), `bioFaunaProductivity` (animals per unit
  flora), `bioCarnPreyMin`/`bioCarnScale` (carnivore prey gate + ramp), `bioFungaMoistRef`/
  `bioFungaFloraWeight`/`bioFungaTempMin` (funga moisture/organic-matter/cold rules); **marine
  flora/fauna**: `bioMarineBase` (0.15, open-ocean baseline density far from land), `bioMarineShelfDepth`
  (2500 m, depth over which shelf/light productivity fades to the base), `bioMarineCoastRings`
  (3, ocean rings from land over which coastal-nutrient richness fades to the base — lower = a
  tighter coastal band, higher = life further offshore);
  slot/point population: `bioFloraSlots`/`bioFaunaSlots`/`bioFungaSlots` (distinct-type cap),
  `bioFloraPoints`/`bioFaunaPoints`/`bioFungaPoints` (point budget at full density, scaled by
  it; Tiny=1…Huge=5), `bioRegionBonus` (how strongly a cell copies same-biome neighbours →
  homogeneity vs variety). To add organisms (incl. marine — give them a `B::Ocean` biome mask
  and `moistMin=0`), append to `biotaArchetypes()` in PlanetBiota.cpp (append-only — indices are
  serialized in v7 saves).
- **Live World (`dayLengthHours`/`yearLengthDays`/`snowTemp`/`seaIceTemp`, `planet.cfg`):**
  `dayLengthHours` (24) sets the day/night period (and the `d/s` rate unit), `yearLengthDays`
  (365.25) the season period; `axialTilt` drives the seasonal declination (0 = no day/night
  tilt). `snowTemp` (0 °C) is the land snow line, `seaIceTemp` (-2 °C) the ocean sea-ice line —
  raise either to grow the white caps. Render constants (night-floor brightness, terminator
  softness, snow-blend ramp) live in `rebuildLiveOverlay()` (src/render/Viewer.cpp), not config.
- **Moons & tides (`tideAmplitude`/`tideSunFactor`, `planet.cfg`):** `tideAmplitude` (0.6 m)
  scales the equilibrium tide per unit tide-raising weight (raise for a more dramatic coastline
  swing); `tideSunFactor` (0.46) is the sun's tide weight vs a unit moon. Moon count (1–3) and
  per-moon orbit/period/inclination/mass are randomized in `generateMoons()` (PlanetOcean.cpp);
  the 3D sun distance/size, moon orbit-render band and eclipse angles are render constants
  (ViewerRender.cpp / `rebuildLiveOverlay`), not config.
- **Volcanoes (`volcano*` in PlanetConfig / `planet.cfg`):** placement by tectonic context —
  `volcanoProbRidge` (0.55), `volcanoProbBorder` (0.06), `volcanoProbInterior` (0.003) are the
  per-cell placement probabilities for young-ridge / plate-border / interior cells (raise for more
  vents of that kind), `volcanoMaxCount` (60) caps the total (reservoir-sampled so the ratios hold).
  Lifecycle — `volcanoInitialBuildMax` (2500 m) pre-builds some vents on entry, `volcanoBuildRate`
  (0.02 m/h at activity 1) grows active vents, `volcanoFreeHeight` (1000 m absolute) protects deep
  vents from dormancy, and `volcanoMaxHeight` (3200 m built) is the soft height where dormancy becomes
  certain. Dormancy/explosions — `volcanoDormancyRate` (1/year scale),
  `volcanoDormantMinYears`/`MaxYears` (120/1200), `volcanoExplodeDropFrac` (0.20),
  `volcanoActivityDecay` (0.70), and `volcanoDeadActivity` (0.05). Ash FX —
  `volcanoBlastRadius` (0.09 rad), `volcanoBlastCloud` (1.5), `volcanoAshMinYears`/`MaxYears`
  (0.5/3), `volcanoAshPuffCellsPerWeek` (2), `volcanoAshCloud` (0.9), and
  `volcanoAshCooling` (6 °C). Marker sizes/colours are render constants (ViewerRender.cpp).
- **Geography / atlas (`geo*` in PlanetConfig / `planet.cfg`):** feature-extraction thresholds —
  `geoContinentMinCells` (40, land component ≥ this = Continent, else Island), `geoSeaMaxCells`
  (60, ocean **basin** ≤ this = Sea, else Ocean), `geoMountainElev` (2500 m, min elevation for a
  mountain-range cell), `geoRangeMinCells` (4, min cells for a named range), `geoRiverMinDischarge`
  (80, min mouth discharge for a named river), and the label-clutter caps `geoMaxRivers` (40) /
  `geoMaxPeaks` (40, largest/highest kept). **Ocean basins** — the connected world ocean is split
  into several named oceans by a distance-from-land watershed: `geoOceanSepRadians` (1.40 rad, min
  angular gap between basin centres — *raise → fewer oceans*, lower → more) and `geoOceanDeep` (4, min
  rings from land for a cell to seed a basin); defaults give ~4–6 oceans on an Earth-like world, 1 on a
  waterworld. Feature names are deduped on the **proper-noun root** (no shared roots across kinds), and
  a new volcanic island is named on the fly (`Planet::nameNewLand`, joins an adjacent landmass or mints
  a fresh Island). Name flavour (syllable banks, a "language" per continent) + label fonts/colours are
  constants in NameGen.cpp / ViewerRender.cpp, not config.
- **Civilization / settlements (`civ*` in PlanetConfig / `planet.cfg`):** placement — `civMaxSettlements`
  (80, cap), `civMinSpacingRadians` (0.10 rad ≈ 640 km, min gap between sites), `civMinHabitability`
  (0.22, don't place below this). Habitability blend — `civHabWaterWeight` (0.45), `civHabFoodWeight`
  (0.40, the rest is temperature comfort), `civHabTempOpt` (18 °C, most comfortable mean), `civHabElevPenalty`
  (2500 m, high terrain steeply penalised above this). Population — `civSeedPopulation` (250, initial
  village), `civGrowthRate` (0.02/yr logistic rate), `civMaxPopulation` (2e6, the carrying capacity at
  habitability 1), tier thresholds `civTownPop` (5000) / `civCityPop` (100000), `civAbandonPop` (50,
  below = abandoned/ruins but can revive). **Dynamics** — `civSiteVariety` (1.0; 0 = flat capacities,
  higher = big rivers/coasts host far larger cities → wide size spread), `civGrowthMin` (0.25, growth-rate
  floor at habitability 0), `civHarvestVar` (0.25, year-to-year harvest swing, scaled by continentality),
  `civDroughtStrength` (0.70) / `civDroughtPeriod` (8 yr) / `civDroughtThresh` (−0.15) / `civDroughtArid`
  (0.50, drought-proneness in arid regions), `civColdYearStrength` (0.50), `civFloodBonus` (0.25, river
  silt), `civFamineRate` (0.15, accelerated loss when food < population), `civStormDeathRate` (0.50) /
  `civHurricaneDeathMult` (3.0, deaths from a storm/hurricane over a town). Droughts/harvests are
  deterministic per (~20° region, year, seed); an active volcano's ash within ~1.5× its blast radius also
  cuts capacity. Marker sizes/colours + hardship tint are render constants (ViewerRender.cpp).
- `upliftGain` (PlanetConfig) — m/tick per unit convergence stress; main
  knob for how fast/high relief builds.
- `relax` (PlanetConfig) — isostatic relaxation toward base elevation. Peaks
  asymptote at `base + perTickUplift/relax`, so raising it lowers/flattens
  the equilibrium; lowering it makes relief taller and slower to settle.
- `beltWidth` (PlanetConfig) — how many cell-rings a mountain belt spreads
  inland (belt width / flank extent).
- `trenchFactor` (Planet::step) — depth multiplier for subduction trenches.
- `driftSpeed` (Planet::assignPlates) — how fast boundary stress builds.
- **Plate lifecycle (PlanetConfig, Phase 2 inc. 1.5):** `splitFraction` (0.20,
  plate share that may rift), `splitProbBase`/`splitProbSlope` (fission prob
  ramp), `splitCheckEvery` (10, iters between periodic checks), `stalemateEps` /
  `stalemateBoost` (deadlock detection + kick), `stalemateWindows` (4, consecutive
  stuck windows before a kick — raise to calm border jitter), `babyMinCells` (4,
  baby blobs smaller than this dissolve as noise), `babyPromoteFrac` (0.7%,
  ridge-strip size to become a real plate), `volcanicLandFrac` / `volcanicElev`
  (land grown on promotion), `landBand` (0.10, soft land-conservation band),
  `miniPlateCells` (50, below = "mini") + `fuseMinPlates` (3, cluster size to fuse
  + steal). Tune these to control how lively / fragmented the plate map stays.
- **Erosion + sea level (PlanetConfig, Phase 2 inc. 2):** `erosionLandRate` (0.08)
  / `erosionSeaRate` (0.02) — fraction/My worn off above / below sea level (raise
  for faster, flatter terrain); `landFractionTarget` (0.30) — geographic land
  goal; `seaLevelStep` (100 m) — fixed nudge per adjustment + `seaLevelTol` (0.02)
  — deadband where sea level rests (raise step or shrink tol for a tighter 30/70,
  but a big step can overshoot a flat "cliff"); `seaLevelEvery` (100) — iterations
  between sea-level updates (higher = more gradual). All editable in `planet.cfg`.
- **Orogeny — taller mountains (PlanetConfig, Phase 2 inc. 4):** `collisionFactor`
  (1.8, continent-continent uplift, Himalaya) and `arcFactor` (1.4, continental
  subduction-arc uplift, Andes) — raise either to make ranges taller/more reliable
  across seeds; `isostaticPersist` (0.85, how strongly high crust resists relax —
  toward 1 = ranges barely erode and continents stay high; lower = more dynamic
  rise/erode) saturating at `rootScale` (2500 m above `continentBase`). These three
  boosts are **drift-only** (gated on `Planet::drifting`); in Phase-2 drift the
  per-tick `erode()` is what limits their height, so they don't rail the clamp.
- **Soft peak cap (drift-only) — no 9000 m plateau:** previously the hard
  `[-11000, 9000]` clamp (in `step()`, `erode()` *and* `hydrology()`) flattened many
  drift-time peaks into a 9000 m plateau. Now growth is **probabilistic** above
  `peakSoftCapStart` (7000 m): the chance a tick's positive uplift "takes" falls
  linearly to 0 at `peakSoftCapEnd` (12000 m), so peaks spread smoothly across a
  height band instead of railing at one ceiling. A **lost** grow roll forfeits that
  tick's uplift *and* shaves a random `0..peakFailDrop` (200 m) off, so a peak hovers
  near its own height (height now tracks orogeny strength: strong seeds reach
  10–11 km, most cluster lower). The hard clamp's **upper bound now tracks
  `peakSoftCapEnd`** in all three places (just a safety rail; lower −11000 m
  unchanged). The roll is a **pure hash of `(cellIndex, erodeIter, seed)`** — never
  touches `rngState`, stays bit-identical across OpenMP thread counts, and since
  `erodeIter` is saved (step/erode run 1:1 in drift) F5/F9 resumes **bit-identical**
  (no save-version bump). **Drift-only** (gated on `drifting`) so Phase-1 forming
  still auto-settles. Tune `peakSoftCapStart` / `peakSoftCapEnd` / `peakFailDrop` in
  `planet.cfg`. Verified headless: smooth 8.5→10.5 km taper, 0 cells pinned at the
  ceiling, determinism + exact resume intact.
- **Seafloor aging->depth (PlanetConfig, Phase 2 inc. 4):** `oceanBase` is now the
  **deep abyssal floor** (-6000 m, not a flat ocean base) and `ridgeDepth` the
  shallow young value (-2500 m); `seafloorSubsidence` (280 m per sqrt(My)) sets how
  fast oceanic crust deepens with `geoAge` (half-space cooling), and
  `seafloorSeedAge` (80 My) is the initial oceanic age spread at generation so the
  starting seafloor already has ridge->abyss variety.
- **Hydrology (PlanetConfig, Phase 3 inc. 1):** `phase3AfterMy` (300) — drift-My
  before the Phase-3 prompt; `phase3DtScale` (0.2) — Phase-3 timestep =
  `cflDtMy()*this` (smaller = finer carving, slower drift per step); `rainfall`
  (1.0) — uniform precip per cell (drainage-area unit; orographic precip is a later
  climate add-on); `riverThreshold` (25) — discharge above which a cell is a river
  (also the river-render threshold); `riverIncision` K (0.02) + `riverDischargeExp`
  m (0.5) + `riverSlopeExp` n (1.0) — stream-power incision `K*Q^m*S^n*dt` (raise K
  for faster valley carving); `riverTransport` (0.1) — transport capacity
  `cap=this*Q*S` and `depFrac` (0.25) — deposition rate of excess load (raise both
  for more deltas / faster lake infill). All editable in `planet.cfg`.

## Conventions

- All code, identifiers, comments and filenames in **English**.
- Before generating code, summarize the approach and ask whether to proceed.
- Prefer **inline code in chat** over attachments; give exact file contents
  rather than long explanations.
- Direct, concrete answers. Metric system throughout.
- C++17, multi-file CMake. Keep simulation logic free of raylib so it stays
  testable headless: engine in `src/sim` (no raylib), all rendering in `src/render`.
- Geometry stays fixed — never make cells move; add new per-cell properties
  and flow them over the existing grid + neighbor adjacency.