feat(dl): add --proxy-download for a separate download proxy

Manifest, licence and auth stay on --proxy; track, subtitle and attachment downloads use the second proxy. Also exposed as proxy_download on the REST download job with the same server_proxy gate. The download session now ignores HTTP(S)_PROXY and copies rnet cookies set by name.

tests/tracks/test_attachment_download.py

@@ -57,3 +57,60 @@ def test_download_with_flag_bypasses_proxy(tmp_path, monkeypatch) -> None:
     assert not proxied.got
     assert direct.got == [URL]
     assert attachment.path is not None and attachment.path.read_bytes() == b"jpegdata"
+
+
+def test_download_with_proxy_download_uses_only_that_proxy(tmp_path, monkeypatch) -> None:
+    monkeypatch.setattr(config.directories, "temp", tmp_path)
+    seen: dict = {}
+
+    def fake_direct(session, proxy=None):
+        seen["proxy"] = proxy
+        return FakeSession(proxies={"all": proxy})
+
+    monkeypatch.setattr(track_module, "direct_session", fake_direct)
+    proxied = FakeSession(proxies={"https": "http://manifest-proxy:1"})
+    attachment = Attachment.from_url(URL, name="thumbnail", session=proxied)
+    attachment.download(proxied, proxy_download="http://dl-proxy:2")
+    assert not proxied.got
+    assert seen["proxy"] == "http://dl-proxy:2"
+    assert proxied.proxies == {"https": "http://manifest-proxy:1"}
+
+
+def test_no_proxy_download_wins_over_proxy_download(tmp_path, monkeypatch) -> None:
+    monkeypatch.setattr(config.directories, "temp", tmp_path)
+    seen: dict = {}
+    monkeypatch.setattr(
+        track_module, "direct_session", lambda s, proxy=None: seen.setdefault("p", proxy) or FakeSession()
+    )
+    plain = FakeSession()
+    Attachment.from_url(URL, name="t", session=plain).download(
+        plain, no_proxy_download=True, proxy_download="http://dl-proxy:2"
+    )
+    assert "p" not in seen and plain.got == [URL]
+
+
+def test_direct_session_routes_through_the_given_proxy() -> None:
+    base = requests.Session()
+    base.headers["X-Test"] = "1"
+    new = track_module.direct_session(base, "http://dl-proxy:2")
+    assert new.headers["X-Test"] == "1"
+    assert new.proxies == {"http": "http://dl-proxy:2", "https": "http://dl-proxy:2"}
+    assert requests.utils.select_proxy("https://cdn.example.com/a", new.proxies) == "http://dl-proxy:2"
+
+
+def test_direct_session_proxy_beats_environment(monkeypatch) -> None:
+    monkeypatch.setenv("HTTPS_PROXY", "http://env-proxy:9")
+    new = track_module.direct_session(requests.Session(), "http://dl-proxy:2")
+    settings = new.merge_environment_settings("https://cdn.example.com/a", {}, None, None, None)
+    assert settings["proxies"]["https"] == "http://dl-proxy:2"
+
+
+def test_direct_session_copies_rnet_cookies_set_by_name() -> None:
+    from unshackle.core.session import RnetSession
+
+    rs = RnetSession()
+    rs.cookies.set("via_set", "1", domain="cdn.example.com")
+    rs.cookies["via_item"] = "3"
+    new = track_module.direct_session(rs, "http://dl-proxy:2")
+    assert new.cookies.get("via_set") == "1"
+    assert new.cookies.get("via_item") == "3"