feat: folder scan — depth-limited natural-sorted image listing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

gates/scan.py

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+"""Pure folder-scan layer for Folder Image Loader. Stdlib only — no torch."""
+import os
+import re
+from pathlib import Path
+
+IMAGE_EXTS = {".png", ".jpg", ".jpeg", ".webp", ".bmp", ".tif", ".tiff"}
+
+
+def natural_key(s):
+    return [int(t) if t.isdigit() else t.lower() for t in re.split(r"(\d+)", s)]
+
+
+def list_images(folder, depth=0):
+    root = Path(folder)
+    if not root.is_dir():
+        raise NotADirectoryError(f"Not a folder: {folder}")
+    root_depth = len(root.parts)
+    results = []
+    for dirpath, dirnames, filenames in os.walk(root):
+        cur = Path(dirpath)
+        rel_depth = len(cur.parts) - root_depth
+        if depth >= 0 and rel_depth >= depth:
+            dirnames[:] = []                    # don't descend past `depth`
+        if depth >= 0 and rel_depth > depth:
+            continue
+        for name in filenames:
+            if Path(name).suffix.lower() in IMAGE_EXTS:
+                results.append(str(cur / name))
+    results.sort(key=lambda p: natural_key(os.path.relpath(p, root)))
+    return results

tests/test_scan.py

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+# tests/test_scan.py
+from gates import scan
+
+def _touch(p, data=b"x"):
+    p.parent.mkdir(parents=True, exist_ok=True)
+    p.write_bytes(data)
+
+def test_natural_sort_orders_numerically():
+    items = ["img10.png", "img2.png", "img1.png"]
+    assert sorted(items, key=scan.natural_key) == ["img1.png", "img2.png", "img10.png"]
+
+def test_list_images_top_level_only_default(tmp_path):
+    _touch(tmp_path / "a.png"); _touch(tmp_path / "b.jpg"); _touch(tmp_path / "note.txt")
+    _touch(tmp_path / "sub" / "c.png")
+    got = [p.split("/")[-1] for p in scan.list_images(str(tmp_path))]
+    assert got == ["a.png", "b.jpg"]            # depth 0: no sub/, no .txt
+
+def test_list_images_depth_one(tmp_path):
+    _touch(tmp_path / "a.png")
+    _touch(tmp_path / "sub" / "c.png")
+    _touch(tmp_path / "sub" / "deep" / "d.png")
+    got = [p.split("/")[-1] for p in scan.list_images(str(tmp_path), depth=1)]
+    assert got == ["a.png", "c.png"]            # depth 1: include sub/, not sub/deep/
+
+def test_list_images_unlimited_depth(tmp_path):
+    _touch(tmp_path / "a.png"); _touch(tmp_path / "sub" / "deep" / "d.png")
+    got = scan.list_images(str(tmp_path), depth=-1)
+    assert len(got) == 2
+
+def test_list_images_natural_sort_by_relpath(tmp_path):
+    for n in ["img1.png", "img2.png", "img10.png"]:
+        _touch(tmp_path / n)
+    got = [p.split("/")[-1] for p in scan.list_images(str(tmp_path))]
+    assert got == ["img1.png", "img2.png", "img10.png"]
+
+def test_list_images_bad_path_raises(tmp_path):
+    import pytest
+    with pytest.raises(NotADirectoryError):
+        scan.list_images(str(tmp_path / "nope"))