feat(ground): accept ground_model.json written before the schema number

- A file with no `schema` key is read as schema 1, but every pier must have a
  `ground` object, so a renamed field is refused instead of loading as empty.
- `schema` null or any other number is still refused.
- The project file keeps the normalised model and checks it with its own
  check (checkStoredGroundModel), so a saved model reopens.
- Temporary: remove the no-schema branch once examples/out is regenerated.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/core/ground-model.ts

@@ -25,21 +25,44 @@ function numOrNull(v: unknown): number | null {
   return typeof v === 'number' && Number.isFinite(v) ? v : null;
 }
 
-/** Checks the shape of a parsed ground_model.json. Throws with the first problem named in Korean. */
+/**
+ * Checks the shape of a parsed ground_model.json. Throws with the first problem named in Korean.
+ * A file with no `schema` key is the layout written before the number was added: it is read as schema 1, and the
+ * `ground` object is required so that a renamed field is refused instead of loading as empty values.
+ * TODO: remove the no-schema branch once the 옛 파일 (examples/out) is regenerated with schema 1.
+ */
 export function checkGroundModel(raw: unknown): GroundModelFile {
   const obj = raw as Partial<GroundModelFile> | null;
   if (!obj || typeof obj !== 'object') throw new Error('지반 모델 파일 형식이 아닙니다.');
-  if (obj.schema !== GROUND_MODEL_SCHEMA) {
+  if (obj.schema !== undefined && obj.schema !== GROUND_MODEL_SCHEMA) {
     throw new Error(`지반 모델 형식 번호 ${String(obj.schema)}을(를) 읽을 수 없습니다 (지원: ${GROUND_MODEL_SCHEMA}).`);
   }
   if (!Array.isArray(obj.piers)) throw new Error('지반 모델 파일에 교각 목록(piers)이 없습니다.');
   const piers = obj.piers.map((p, i) => {
     const id = (p as { id?: unknown })?.id;
     if (typeof id !== 'string' || !id) throw new Error(`지반 모델 ${i + 1}번째 교각의 이름(id)이 없습니다.`);
-    const ground = (p as { ground?: { center?: unknown; excel?: unknown } }).ground ?? {};
+    const ground = (p as { ground?: { center?: unknown; excel?: unknown } }).ground;
+    if (!ground || typeof ground !== 'object') throw new Error(`지반 모델 ${id}: 지반 값(ground)이 없습니다.`);
     return { id, centerEl: numOrNull(ground.center), excelEl: numOrNull(ground.excel) };
   });
-  return { schema: obj.schema, generated: typeof obj.generated === 'string' ? obj.generated : '', piers };
+  return { schema: GROUND_MODEL_SCHEMA, generated: typeof obj.generated === 'string' ? obj.generated : '', piers };
+}
+
+/**
+ * Checks the normalised model stored in a project file (the form checkGroundModel returns). The project keeps this
+ * form, not the raw ground_model.json, so it is checked separately.
+ */
+export function checkStoredGroundModel(raw: unknown): GroundModelFile {
+  const obj = raw as Partial<GroundModelFile> | null;
+  if (!obj || typeof obj !== 'object' || obj.schema !== GROUND_MODEL_SCHEMA) {
+    throw new Error('프로젝트 안의 지반 모델 형식 번호가 맞지 않습니다.');
+  }
+  if (!Array.isArray(obj.piers)) throw new Error('프로젝트 안의 지반 모델에 교각 목록이 없습니다.');
+  for (const p of obj.piers as Partial<GroundModelPier>[]) {
+    const ok = typeof p?.id === 'string' && (p.centerEl === null || typeof p.centerEl === 'number') && (p.excelEl === null || typeof p.excelEl === 'number');
+    if (!ok) throw new Error(`프로젝트 안의 지반 모델 교각 ${String(p?.id)}의 값이 맞지 않습니다.`);
+  }
+  return obj as GroundModelFile;
 }
 
 /** Parses the file text. Throws when it is not JSON or does not match the schema. */

src/core/project.ts

@@ -1,5 +1,5 @@
 import type { FckByMember, Material } from './rebar/common';
-import { checkGroundModel, type GroundModelFile } from './ground-model';
+import { checkStoredGroundModel, type GroundModelFile } from './ground-model';
 import type { PierInput } from './types';
 
 /** Project file schema (spec §8). Bump only with a migration. */
@@ -71,7 +71,7 @@ export function parseProject(text: string): ProjectFile {
       }
     }
   }
-  if (obj.groundModel !== undefined) checkGroundModel(obj.groundModel);
+  if (obj.groundModel !== undefined) checkStoredGroundModel(obj.groundModel);
   obj.piers.forEach((p, i) => {
     if (!p || typeof p.id !== 'string' || !p.input) throw new Error(`교각 ${i + 1}: id 또는 input이 없습니다.`);
     const input = p.input;