feat(sync): wire state.json + divergence detection + dialogs

state.py: per-instance sync state. <pack>/.cloud-sync/state.json
(mode 600) records last_pulled_snapshot_id + last_pulled_at +
host_tag. Versioned schema. clear() on remote-empty.

sync.pull decision tree (replaces the unconditional restore):

  no token file
    → prompt_login_qt; on Skip return 0 (don't block launch)
  no state + remote empty
    → no-op
  no state + remote non-empty
    → restore (first-run on this machine)
  state.id == remote.id
    → skip restore (up to date)
  state.id != remote.id, no in-scope local edits since state.at
    → restore (fast-forward)
  state.id != remote.id, in-scope local edits since state.at
    → prompt_conflict_qt
      keep_local  → don't restore; push will overwrite cloud
      use_remote  → restore + update state
      cancel      → exit 1

sync.push: --json output parsed for snapshot_id; state.json updated
to that id after a successful backup. Skips silently if no token.

_find_modified_in_scope: walks include roots, filters via
_matches_any (restic-style globs: dir/, **/dir/, **/*.glob).
Stops at 50 hits; we only need 'any' + a sample for the dialog.

_format_dt: hand-rolled (no GNU-vs-Windows strftime quirks) →
'Thursday, October 21, 2021 at 7:12 PM'.

Restic JSON parsing helpers: _parse_snapshots, _parse_restic_time
(handles nanosecond precision), _parse_backup_summary.

tests/test_state.py: 19 new tests covering state read/write, scope-
aware mtime walk, exclude glob matching, restic output parsers.
Total: 52 green.

tests/test_state.py

@@ -0,0 +1,192 @@
+"""state.json read/write + divergence helpers."""
+
+from __future__ import annotations
+
+import json
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+import pytest
+
+from cloud_sync import scope as scopemod
+from cloud_sync import state as statemod
+from cloud_sync.sync import (
+    _find_modified_in_scope,
+    _format_dt,
+    _matches_any,
+    _parse_backup_summary,
+    _parse_restic_time,
+    _parse_snapshots,
+)
+
+
+# ---- state.read/write ----
+
+
+def test_read_missing_returns_none(tmp_path: Path):
+    assert statemod.read(tmp_path) is None
+
+
+def test_write_then_read_roundtrip(tmp_path: Path):
+    dt = datetime(2026, 6, 5, 12, 34, 56, tzinfo=timezone.utc)
+    statemod.write(
+        tmp_path,
+        statemod.State(last_pulled_snapshot_id="abc123", last_pulled_at=dt),
+    )
+    got = statemod.read(tmp_path)
+    assert got is not None
+    assert got.last_pulled_snapshot_id == "abc123"
+    assert got.last_pulled_at == dt
+
+
+def test_write_sets_mode_600(tmp_path: Path):
+    statemod.write(
+        tmp_path,
+        statemod.State(
+            last_pulled_snapshot_id="x",
+            last_pulled_at=datetime.now(timezone.utc),
+        ),
+    )
+    mode = statemod.state_path(tmp_path).stat().st_mode & 0o777
+    assert mode == 0o600
+
+
+def test_clear_idempotent(tmp_path: Path):
+    statemod.clear(tmp_path)  # no-op when missing
+    statemod.write(
+        tmp_path,
+        statemod.State(
+            last_pulled_snapshot_id="x",
+            last_pulled_at=datetime.now(timezone.utc),
+        ),
+    )
+    assert statemod.state_path(tmp_path).exists()
+    statemod.clear(tmp_path)
+    assert not statemod.state_path(tmp_path).exists()
+
+
+def test_wrong_schema_returns_none(tmp_path: Path):
+    p = tmp_path / ".cloud-sync" / "state.json"
+    p.parent.mkdir(parents=True)
+    p.write_text(
+        json.dumps({"schema": 999, "last_pulled_snapshot_id": "x", "last_pulled_at": "2026-01-01T00:00:00Z"})
+    )
+    assert statemod.read(tmp_path) is None
+
+
+def test_garbage_json_returns_none(tmp_path: Path):
+    p = tmp_path / ".cloud-sync" / "state.json"
+    p.parent.mkdir(parents=True)
+    p.write_text("{not json")
+    assert statemod.read(tmp_path) is None
+
+
+# ---- _find_modified_in_scope ----
+
+
+def _touch(p: Path, content: str = "x") -> None:
+    p.parent.mkdir(parents=True, exist_ok=True)
+    p.write_text(content)
+
+
+def test_no_in_scope_changes_returns_empty(tmp_path: Path):
+    _touch(tmp_path / "options.txt")
+    # mtime is "now", `since` is the future
+    future = datetime.now(timezone.utc) + timedelta(hours=1)
+    hits = _find_modified_in_scope(tmp_path, scopemod.Scope(), future)
+    assert hits == []
+
+
+def test_in_scope_file_modified_after_since_detected(tmp_path: Path):
+    _touch(tmp_path / "options.txt")
+    past = datetime.now(timezone.utc) - timedelta(hours=1)
+    hits = _find_modified_in_scope(tmp_path, scopemod.Scope(), past)
+    assert any(rel.name == "options.txt" for rel, _ in hits)
+
+
+def test_excluded_path_skipped(tmp_path: Path):
+    # config/packwiz-installer.log matches exclude "**/*.log" AND "config/packwiz*"
+    _touch(tmp_path / "config" / "packwiz-installer.log")
+    past = datetime.now(timezone.utc) - timedelta(hours=1)
+    hits = _find_modified_in_scope(tmp_path, scopemod.Scope(), past)
+    assert hits == []
+
+
+def test_only_excluded_changes_not_a_conflict(tmp_path: Path):
+    _touch(tmp_path / ".cloud-sync" / "files-from.txt")  # excluded
+    _touch(tmp_path / "config" / "packwiz-installer.log")  # excluded
+    past = datetime.now(timezone.utc) - timedelta(hours=1)
+    hits = _find_modified_in_scope(tmp_path, scopemod.Scope(), past)
+    assert hits == []
+
+
+def test_walks_subdirectories(tmp_path: Path):
+    _touch(tmp_path / "config" / "fabric" / "custom.json")
+    past = datetime.now(timezone.utc) - timedelta(hours=1)
+    hits = _find_modified_in_scope(tmp_path, scopemod.Scope(), past)
+    assert any("custom.json" in str(rel) for rel, _ in hits)
+
+
+# ---- _matches_any ----
+
+
+def test_dir_pattern_matches_anything_under(tmp_path: Path):
+    assert _matches_any(Path(".cloud-sync/token"), [".cloud-sync/"])
+    assert _matches_any(Path("a/b/cache/x"), ["**/cache/"])
+    assert not _matches_any(Path("config/options.txt"), [".cloud-sync/"])
+
+
+def test_glob_pattern(tmp_path: Path):
+    assert _matches_any(Path("config/packwiz-installer.log"), ["config/packwiz*"])
+    assert _matches_any(Path("foo/bar.log"), ["**/*.log"])
+
+
+# ---- restic output parsing ----
+
+
+def test_parse_snapshots_empty():
+    assert _parse_snapshots("") == []
+    assert _parse_snapshots("null") == []
+    assert _parse_snapshots("[]") == []
+
+
+def test_parse_snapshots_one():
+    out = json.dumps([{"id": "abc", "time": "2026-06-05T12:00:00Z"}])
+    parsed = _parse_snapshots(out)
+    assert len(parsed) == 1
+    assert parsed[0]["id"] == "abc"
+
+
+def test_parse_restic_time_with_nanos():
+    dt = _parse_restic_time("2026-06-04T18:33:21.123456789Z")
+    assert dt.tzinfo is timezone.utc
+    assert dt.year == 2026 and dt.day == 4 and dt.hour == 18
+
+
+def test_parse_backup_summary_finds_snapshot_id():
+    out = (
+        '{"message_type":"status","percent_done":0.5}\n'
+        '{"message_type":"status","percent_done":1.0}\n'
+        '{"message_type":"summary","snapshot_id":"deadbeef","files_new":3}\n'
+    )
+    assert _parse_backup_summary(out) == "deadbeef"
+
+
+def test_parse_backup_summary_missing_returns_none():
+    assert _parse_backup_summary("") is None
+    assert _parse_backup_summary("not json\nstill not json") is None
+
+
+# ---- _format_dt ----
+
+
+def test_format_dt_strips_leading_zero_on_hour():
+    # 7:12 PM, not 07:12 PM. Day of month also no leading zero.
+    dt = datetime(2021, 10, 21, 19, 12, tzinfo=timezone.utc)
+    out = _format_dt(dt)
+    # Output is local-time-converted, so don't pin the weekday/AM-PM exactly
+    # in case CI runs UTC vs PT; just check the formatting shape.
+    assert "October" in out or "Oct" not in out  # full month name
+    assert ", 2021 at" in out
+    assert " AM" in out or " PM" in out
+    assert " 0:" not in out  # no leading-zero hour