Rewrite frontend types and HTTP client in src.

Export names match the leftover pages. Billing HTTP wrappers stay so
gateway seams are not restyled here.

tests/test_periscope_frontend_lib_rewrite.py

@@ -0,0 +1,39 @@
+"""Native frontend types and API client live under periscope/src."""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+SRC = ROOT / "periscope" / "src" / "frontend" / "src" / "lib"
+DEP = ROOT / "periscope" / "dependency" / "frontend" / "src" / "lib"
+
+
+def _exports(path: Path) -> set[str]:
+    text = path.read_text(encoding="utf-8")
+    names = set(re.findall(r"^export (?:async )?function (\w+)", text, re.M))
+    names |= set(re.findall(r"^export (?:interface|type|class|const) (\w+)", text, re.M))
+    return names
+
+
+def test_frontend_lib_is_src():
+    for name in ("api.ts", "types.ts", "utils.ts"):
+        path = SRC / name
+        assert path.is_file(), name
+        head = path.read_text(encoding="utf-8")[:400]
+        assert "Native Periscope overlay" not in head
+
+
+def test_api_keeps_page_exports():
+    src = _exports(SRC / "api.ts")
+    dep = _exports(DEP / "api.ts")
+    missing = dep - src
+    assert not missing, sorted(missing)
+
+
+def test_types_keep_page_exports():
+    src = _exports(SRC / "types.ts")
+    dep = _exports(DEP / "types.ts")
+    missing = dep - src
+    assert not missing, sorted(missing)