feat(wiki): concept schema loader + concepts.yaml (F-12)

Adds wiki/concepts.yaml (5 curated seeds: discrete-conformal-map,
circle-packing, lobachevsky-function, discrete-yamabe-flow,
hyperideal-tetrahedron) and codex/wiki.py with full load_concepts()
implementation (Concept dataclass, YAML parser, graceful empty list).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/wiki/test_concepts.py

@@ -0,0 +1,122 @@
+"""Tests for load_concepts() — YAML parsing of wiki/concepts.yaml."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+import pytest
+
+from codex.wiki import Concept, load_concepts
+
+# ---------------------------------------------------------------------------
+# Fixtures
+# ---------------------------------------------------------------------------
+
+FIXTURE_YAML = textwrap.dedent(
+    """\
+    concepts:
+      - slug: discrete-conformal-map
+        title: Discrete Conformal Map
+        aliases: [discrete conformal equivalence, discrete uniformization]
+        emphasis: Fokus auf die variationelle Charakterisierung (BPS 2015).
+      - slug: circle-packing
+        title: Circle Packing
+        aliases: [Koebe-Andreev-Thurston, circle pattern]
+      - slug: lobachevsky-function
+        title: Lobachevsky Function
+        aliases: [Milnor Lobachevsky, Clausen function]
+        emphasis: Verwendung in hyperbolischen Volumenformeln (Springborn 2008).
+      - slug: discrete-yamabe-flow
+        title: Discrete Yamabe Flow
+        aliases: [discrete Ricci flow, Chow-Luo]
+      - slug: hyperideal-tetrahedron
+        title: Hyperideal Tetrahedron
+        aliases: [hyperbolic volume, Schläfli, Ushijima]
+    """
+)
+
+
+@pytest.fixture
+def concepts_yaml(tmp_path: Path) -> Path:
+    """Write fixture YAML to a temp file and return the path."""
+    p = tmp_path / "concepts.yaml"
+    p.write_text(FIXTURE_YAML, encoding="utf-8")
+    return p
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+
+def test_load_concepts_returns_all_concepts(concepts_yaml: Path) -> None:
+    """All five concept entries are returned."""
+    concepts = load_concepts(str(concepts_yaml))
+    assert len(concepts) == 5
+
+
+def test_load_concepts_types(concepts_yaml: Path) -> None:
+    """Every returned item is a Concept instance."""
+    concepts = load_concepts(str(concepts_yaml))
+    for c in concepts:
+        assert isinstance(c, Concept)
+
+
+def test_load_concepts_first_slug_and_title(concepts_yaml: Path) -> None:
+    """First concept has correct slug and title."""
+    concepts = load_concepts(str(concepts_yaml))
+    assert concepts[0].slug == "discrete-conformal-map"
+    assert concepts[0].title == "Discrete Conformal Map"
+
+
+def test_load_concepts_aliases_are_lists(concepts_yaml: Path) -> None:
+    """Aliases are parsed as a list of strings."""
+    concepts = load_concepts(str(concepts_yaml))
+    for c in concepts:
+        assert isinstance(c.aliases, list)
+        for alias in c.aliases:
+            assert isinstance(alias, str)
+
+
+def test_load_concepts_first_has_two_aliases(concepts_yaml: Path) -> None:
+    """First concept has exactly two aliases."""
+    concepts = load_concepts(str(concepts_yaml))
+    assert concepts[0].aliases == ["discrete conformal equivalence", "discrete uniformization"]
+
+
+def test_load_concepts_emphasis_present(concepts_yaml: Path) -> None:
+    """Concepts with emphasis field have it parsed correctly."""
+    concepts = load_concepts(str(concepts_yaml))
+    dcm = next(c for c in concepts if c.slug == "discrete-conformal-map")
+    assert dcm.emphasis is not None
+    assert "variationelle" in dcm.emphasis
+
+
+def test_load_concepts_emphasis_absent_is_none(concepts_yaml: Path) -> None:
+    """Concepts without emphasis field have emphasis=None."""
+    concepts = load_concepts(str(concepts_yaml))
+    cp = next(c for c in concepts if c.slug == "circle-packing")
+    assert cp.emphasis is None
+
+
+def test_load_concepts_slugs_unique(concepts_yaml: Path) -> None:
+    """All slugs are distinct."""
+    concepts = load_concepts(str(concepts_yaml))
+    slugs = [c.slug for c in concepts]
+    assert len(slugs) == len(set(slugs))
+
+
+def test_load_concepts_unicode_in_aliases(concepts_yaml: Path) -> None:
+    """Aliases with non-ASCII characters (Schläfli) are parsed without error."""
+    concepts = load_concepts(str(concepts_yaml))
+    ht = next(c for c in concepts if c.slug == "hyperideal-tetrahedron")
+    assert any("Schläfli" in a for a in ht.aliases)
+
+
+def test_load_concepts_empty_yaml(tmp_path: Path) -> None:
+    """An empty concepts list returns an empty list (no crash)."""
+    p = tmp_path / "concepts.yaml"
+    p.write_text("concepts: []\n", encoding="utf-8")
+    concepts = load_concepts(str(p))
+    assert concepts == []