feat: serve responsive WebP srcsets for faster mobile browsing

On-demand ?w= resize with a disk cache under webcache/; downloads stay full-resolution.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/conftest.py

@@ -14,7 +14,8 @@ def data_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
     intermediates = tmp_path / "intermediates"
     meta = tmp_path / "meta"
     inbox = tmp_path / "incoming"
-    for directory in (variants, intermediates, meta, inbox):
+    webcache = tmp_path / "webcache"
+    for directory in (variants, intermediates, meta, inbox, webcache):
         directory.mkdir()
 
     monkeypatch.setattr("app.config.DATA_DIR", tmp_path)
@@ -22,5 +23,6 @@ def data_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
     monkeypatch.setattr("app.config.INTERMEDIATES_DIR", intermediates)
     monkeypatch.setattr("app.config.META_DIR", meta)
     monkeypatch.setattr("app.config.INBOX_DIR", inbox)
+    monkeypatch.setattr("app.config.WEB_CACHE_DIR", webcache)
     monkeypatch.setattr("app.config.PROCESSED_FILE", tmp_path / "processed.json")
     return tmp_path

tests/test_main.py

@@ -5,10 +5,11 @@ from __future__ import annotations
 from pathlib import Path
 
 import pytest
-from app import config, pipeline
+from app import config, images, pipeline
 from app.main import _safe_job_file, _validate_job_id, app
 from fastapi import HTTPException
 from fastapi.testclient import TestClient
+from PIL import Image
 
 
 @pytest.fixture
@@ -16,6 +17,11 @@ def client(data_dir: Path) -> TestClient:
     return TestClient(app)
 
 
+def _write_test_png(path: Path, size: tuple[int, int] = (1200, 800)) -> None:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    Image.new("RGB", size, color=(40, 80, 120)).save(path, format="PNG")
+
+
 def test_validate_job_id_sanitizes_input() -> None:
     assert _validate_job_id("foo@bar") == "foo_bar"
     assert _validate_job_id("photo01") == "photo01"
@@ -50,3 +56,48 @@ def test_index_empty(client: TestClient) -> None:
 def test_job_not_found(client: TestClient) -> None:
     response = client.get("/jobs/does-not-exist")
     assert response.status_code == 404
+
+
+def test_job_file_srcset_resize(client: TestClient, data_dir: Path) -> None:
+    stem = "photo01"
+    paths = pipeline.job_paths(stem)
+    png = paths.variants / f"{stem}_v1.png"
+    _write_test_png(png)
+    pipeline.write_status(paths, "done", created_at="2026-01-01T00:00:00")
+    pipeline.write_manifest(
+        paths,
+        {
+            "variants": [{"id": "v1", "file": png.name}],
+            "created_at": "2026-01-01T00:00:00",
+        },
+    )
+
+    full = client.get(f"/jobs/{stem}/files/{png.name}")
+    assert full.status_code == 200
+    assert full.headers["content-type"].startswith("image/")
+
+    bad = client.get(f"/jobs/{stem}/files/{png.name}?w=999")
+    assert bad.status_code == 400
+
+    resized = client.get(f"/jobs/{stem}/files/{png.name}?w=320")
+    assert resized.status_code == 200
+    assert resized.headers["content-type"] == "image/webp"
+    assert len(resized.content) < len(full.content)
+
+    cached = config.WEB_CACHE_DIR / f"{png.name}.w320.webp"
+    assert cached.is_file()
+    with Image.open(cached) as img:
+        assert img.width == 320
+
+    index = client.get("/")
+    assert index.status_code == 200
+    assert f"/jobs/{stem}/files/{png.name}?w=640" in index.text
+    assert "srcset=" in index.text
+    assert "data-full-src=" in index.text
+
+
+def test_img_attrs_builds_srcset() -> None:
+    attrs = images.img_attrs("job1", "job1_v1.png")
+    assert attrs["src"].endswith("?w=640")
+    assert "320w" in attrs["srcset"]
+    assert attrs["full_src"].endswith("?w=1280")