feat: initial Dropbox tag sync tool

Cross-platform CLI that mirrors Dropbox web tags to OS-native tags:
- macOS: Finder xattrs (content-preserving, no re-upload)
- Windows: XMP:Subject via ExifTool (re-upload expected once per file)

Includes an interactive wizard that auto-detects the OS and Dropbox
folder, walks the user through read-only token creation, previews
tagged files, applies tags, and installs a background scheduler
(launchd on macOS, Task Scheduler on Windows).

Ships with:
- 47-test suite (pytest) covering config, state DB, run_sync, writers
- Gitea Actions CI for Linux / macOS / Windows with coverage reporting

tests/test_platform_macos.py

@@ -0,0 +1,140 @@
+"""Tests for tagsync.platform_macos.
+
+The plist encoding test runs anywhere. The xattr round-trip runs only on
+systems where the extended-attribute syscalls are available (macOS and
+most Linux filesystems).
+"""
+from __future__ import annotations
+
+import os
+import plistlib
+import sys
+from pathlib import Path
+
+import pytest
+
+from tagsync.platform_macos import FINDER_TAGS_XATTR, MacWriter
+
+
+def test_mac_writer_supports_all_file_types():
+    w = MacWriter()
+    for path in ("a.jpg", "b.zip", "c.txt", "noextension"):
+        assert w.supports(Path(path))
+
+
+def test_mac_writer_is_online_only_is_false():
+    w = MacWriter()
+    assert w.is_online_only(Path("/any/file")) is False
+
+
+def test_plist_encoding_matches_finder_format():
+    """Finder expects a binary plist of a string array."""
+    from tagsync.platform_macos import plistlib  # re-export
+    tags = ["alpha", "beta", "gamma"]
+    encoded = plistlib.dumps(tags, fmt=plistlib.FMT_BINARY)
+    # Binary plists start with 'bplist'.
+    assert encoded.startswith(b"bplist")
+    decoded = plistlib.loads(encoded)
+    assert decoded == tags
+
+
+def _xattr_supported(path: Path) -> bool:
+    """Can we setxattr / getxattr on files in this directory?"""
+    if not hasattr(os, "setxattr") or not hasattr(os, "getxattr"):
+        return False
+    try:
+        # Use a neutral namespace; on Linux, user.* always works on ext4.
+        os.setxattr(path, "user.tagsync_probe", b"ok")
+        val = os.getxattr(path, "user.tagsync_probe")
+        os.removexattr(path, "user.tagsync_probe")
+        return val == b"ok"
+    except OSError:
+        return False
+
+
+@pytest.fixture
+def xattr_capable_file(tmp_path):
+    f = tmp_path / "target"
+    f.touch()
+    if not _xattr_supported(f):
+        pytest.skip("filesystem does not support extended attributes")
+    return f
+
+
+def test_write_and_read_tags_via_xattr(xattr_capable_file):
+    """Round-trip the actual xattr the script uses in production.
+
+    On Linux, the 'com.apple.metadata:*' namespace may not be allowed,
+    so this test uses the MacWriter only on Darwin.
+    """
+    if sys.platform != "darwin":
+        pytest.skip("Finder xattr namespace only writable on macOS")
+
+    w = MacWriter()
+    w.write_tags(xattr_capable_file, ["alpha", "beta"])
+
+    raw = os.getxattr(xattr_capable_file, FINDER_TAGS_XATTR)
+    assert plistlib.loads(raw) == ["alpha", "beta"]
+
+
+def test_clear_tags_via_xattr(xattr_capable_file):
+    if sys.platform != "darwin":
+        pytest.skip("Finder xattr namespace only writable on macOS")
+
+    w = MacWriter()
+    w.write_tags(xattr_capable_file, ["alpha"])
+    w.write_tags(xattr_capable_file, [])
+
+    with pytest.raises(OSError):
+        os.getxattr(xattr_capable_file, FINDER_TAGS_XATTR)
+
+
+def test_clear_tags_when_none_set_is_noop(tmp_path):
+    """Removing a non-existent xattr should not raise."""
+    if sys.platform != "darwin":
+        pytest.skip("requires macOS xattr semantics")
+    f = tmp_path / "fresh"
+    f.touch()
+    MacWriter().write_tags(f, [])  # should not raise
+
+
+# --- launchd plist generation -----------------------------------------------
+
+
+def test_install_schedule_writes_plist(tmp_path, monkeypatch):
+    """We don't want to actually call launchctl; intercept it and verify
+    the plist contents."""
+    import tagsync.platform_macos as pm
+
+    calls = []
+
+    class FakeResult:
+        returncode = 0
+        stderr = ""
+        stdout = ""
+
+    monkeypatch.setattr(pm.subprocess, "run", lambda args, **kw: calls.append(args) or FakeResult())
+
+    # Redirect plist + log paths into tmp to avoid touching real HOME.
+    fake_plist = tmp_path / "agent.plist"
+    fake_log = tmp_path / "log"
+    monkeypatch.setattr(pm, "LAUNCHD_PLIST", fake_plist)
+    monkeypatch.setattr(pm, "LOG_PATH", fake_log)
+
+    entry = tmp_path / "tagsync.py"
+    entry.write_text("# placeholder")
+
+    result_path = pm.install_schedule(entry, interval_minutes=30)
+    assert result_path == fake_plist
+    content = fake_plist.read_text()
+    assert "StartInterval" in content
+    assert "1800" in content  # 30 min -> 1800 sec
+    assert str(entry) in content
+    assert "launchctl" in " ".join(" ".join(c) for c in calls)
+
+
+def test_uninstall_schedule_when_not_installed(tmp_path, monkeypatch):
+    import tagsync.platform_macos as pm
+
+    monkeypatch.setattr(pm, "LAUNCHD_PLIST", tmp_path / "missing.plist")
+    assert pm.uninstall_schedule() is False