feat: support shared-workspace file flow for matrix

tests/adapter/matrix/test_files.py

@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+from pathlib import Path
+from types import SimpleNamespace
+
+from adapter.matrix.files import build_workspace_attachment_path, download_matrix_attachment
+from core.protocol import Attachment
+
+
+def test_build_workspace_attachment_path_scopes_by_surface_user_and_room(tmp_path: Path):
+    rel_path, abs_path = build_workspace_attachment_path(
+        workspace_root=tmp_path,
+        matrix_user_id="@alice:example.org",
+        room_id="!room:example.org",
+        filename="report.pdf",
+        timestamp="20260420-153000",
+    )
+
+    assert (
+        rel_path
+        == "surfaces/matrix/alice_example.org/room_example.org/inbox/20260420-153000-report.pdf"
+    )
+    assert abs_path == tmp_path / rel_path
+
+
+async def test_download_matrix_attachment_persists_file_and_returns_workspace_path(tmp_path: Path):
+    async def download(url: str):
+        assert url == "mxc://server/id"
+        return SimpleNamespace(body=b"%PDF-1.7")
+
+    client = SimpleNamespace(download=download)
+    attachment = Attachment(
+        type="document",
+        url="mxc://server/id",
+        filename="report.pdf",
+        mime_type="application/pdf",
+    )
+
+    saved = await download_matrix_attachment(
+        client=client,
+        workspace_root=tmp_path,
+        matrix_user_id="@alice:example.org",
+        room_id="!room:example.org",
+        attachment=attachment,
+        timestamp="20260420-153000",
+    )
+
+    assert saved.workspace_path is not None
+    assert saved.workspace_path.endswith("20260420-153000-report.pdf")
+    assert (tmp_path / saved.workspace_path).read_bytes() == b"%PDF-1.7"