docs: sync nexus repo truth and audit legacy matrix (#689)

tests/test_repo_truth.py

@@ -0,0 +1,35 @@
+from pathlib import Path
+
+
+def test_readme_states_repo_truth_and_single_canonical_3d_repo() -> None:
+    readme = Path("README.md").read_text()
+
+    assert "current `main` does not ship a browser 3D world" in readme
+    assert "Timmy_Foundation/the-nexus is the only canonical 3D repo" in readme
+    assert "/Users/apayne/the-matrix" in readme
+    assert "npx serve . -l 3000" not in readme
+
+
+def test_claude_doc_matches_current_repo_truth() -> None:
+    claude = Path("CLAUDE.md").read_text()
+
+    assert "Do not describe this repo as a live browser app on `main`." in claude
+    assert "Timmy_Foundation/the-nexus is the only canonical 3D repo." in claude
+    assert "LEGACY_MATRIX_AUDIT.md" in claude
+
+
+def test_legacy_matrix_audit_exists_and_names_rescue_targets() -> None:
+    audit = Path("LEGACY_MATRIX_AUDIT.md").read_text()
+
+    for term in [
+        "agent-defs.js",
+        "agents.js",
+        "avatar.js",
+        "ui.js",
+        "websocket.js",
+        "transcript.js",
+        "ambient.js",
+        "satflow.js",
+        "economy.js",
+    ]:
+        assert term in audit