---
title: "Workshop Brief: Tile Derivation Contract (Q-101)"
description: "Resolve Q-101 — how a coarse Layer-1 cell + seed becomes coherent ~1m voxel geometry across ~3 scale jumps, deterministically. The keystone of the 'what's in a tile' question."
type: workshop
status: active
workshop: tile-derivation-contract
created: 2026-06-07
decision_refs: [D-227, D-228]
---

# Workshop Brief: Tile Derivation Contract (Q-101)

## The question

The generation cascade is built down through Layer 4 (heightmap → drainage → economy →
settlement → quarter skeleton + per-building tags). The **tile itself (Layer 5) is the one
unbuilt layer** — and the design stalled at **Q-101**, the keystone:

> How does a coarse, map-scale hint (a ~78 km Layer-1 cell) plus a seed become fine,
> ~1 m-voxel **coherent** geometry — deterministically (D-010), without "squaring" (visible
> grid artifacts at scale boundaries) — across ~3 scale jumps:
> **78 km cell → ~1 km region → 64 m chunk → 1 m voxel**?

The frame is already decided:
- **D-227** — derive-don't-store: `subtile(x,y,z) = derive(seed, atlas, pos)`, recomputed on
  demand + cached, never persisted; volumetric voxels (1 m) / subvoxels (0.5 m); surface +
  subsurface. Only tile-mutators are saved.
- **D-228** — a tile is orthogonal derived axes (`TerrainMaterial`/`FloorMaterial`/`Vegetation`/
  `Water`/`elevation`); named types are display labels; snow/ice are seasonal region state.

What's **open**: the *how* — the inter-layer hint+seed→geometry API (Tyre sketched a
`RegionHint`) and a **context-driven morphology algorithm family** (≥6 distinct algorithms
selected by local context: rivers meander in lowlands / incise in mountains; coasts dune /
crag / fjord by slope + lithology + glaciation; etc.).

Adjacent open questions to keep in view (not the focus, but the contract must not preclude them):
Q-102 (cohesion matrix — seam-free variation), Q-103 (tile-mutator op schema), Q-105 (region
seasonal/clock state).

**Deliverable:** a resolution for Q-101 → a D-record (claim a fresh `D` in the architecture
domain) defining (a) the `RegionHint`/refinement API across the scale jumps, (b) the morphology
algorithm-family selection model, (c) the anti-squaring / cross-scale-coherence approach, within
the D-010 determinism + D-227 perf (~<5 ms/chunk) constraints.

## Participants

Tyre, Gestalt, Troblum, Miri  (+ Qatux documenting)

## Questions for participants

**Tyre** (architect — owns the inter-layer API):
1. The `RegionHint` shape: what does each layer hand *down* the chain (78 km → region → chunk →
   voxel)? Sketch the refinement-function signature(s) and what state each scale carries.
2. The anti-"squaring" mechanism — how do adjacent cells/chunks derive coherently at their shared
   boundary without seams or visible grid? (domain warping? overlapping kernels? boundary
   blending?) How does this compose with the D-227 by-chunk cache + eviction?
3. The determinism + perf contract: how does `derive(hint, seed, pos)` stay pure (D-010) and hit
   the per-chunk budget?

**Gestalt** (systems — the morphology family + fun):
1. Enumerate the ≥6 distinct morphology algorithms and the **local context** that selects each
   (slope, lithology, glaciation, drainage, climate). Where are the boundaries between families?
2. What makes the *derived* terrain tactically interesting (cover, LOS, chokepoints,
   verticality) — i.e. the game-feel constraints the contract must serve, not just plausibility.

**Troblum** (tech second opinion — feasibility/perf):
1. Algorithmic morphology vs noise fields: which parts of Q-101 are best served by explicit
   morphology algorithms vs multi-octave/domain-warped noise? Cross-scale coherence techniques.
2. Stress-test Tyre's API + the <5 ms/chunk + determinism claims; where does it break at scale?

**Miri** (worldbuilder — believability):
1. Does the morphology family produce worlds that *read true* (rivers behave, coasts vary by
   geology, biomes cohere)? What real-world morphology must the family honor to avoid uncanny terrain?
2. The D-228 derived-label layer — which named features matter for the wiki/atlas to stay consistent.

## Workshop Format

**Round 1 — independent positions.** Each participant writes their answer to disk at
`docs/workshops/tile-derivation-contract/{agent}-round1.md`. No cross-talk yet.

**Round 2 — synthesis.** After a user checkpoint, converge: Tyre + Troblum lock the `RegionHint`
API + coherence approach; Gestalt + Miri lock the morphology family + selection model; resolve
tensions. Qatux drafts the Q-101 resolution + the new D-record.

(Lean 2-round design pass, not the full 5-round format — Q-101 is one focused contract.)