test(coverage): add FuzzyAnchor and HistoryManager unit tests

- test_fuzzy_anchor.py: 6 tests for fuzzy slice resolution
- test_history_manager.py: 8 tests for undo/redo and UISnapshot roundtrip

tests/test_fuzzy_anchor.py

@@ -0,0 +1,59 @@
+import pytest
+from src.fuzzy_anchor import FuzzyAnchor
+
+
+class TestFuzzyAnchor:
+    def test_create_slice_basic(self):
+        text = "line0\nline1\nline2\nline3\nline4\n"
+        result = FuzzyAnchor.create_slice(text, 2, 4)
+        assert "start_line" in result
+        assert "end_line" in result
+        assert "content_hash" in result
+        assert "start_context" in result
+        assert "end_context" in result
+        assert result["start_line"] == 2
+        assert result["end_line"] == 4
+        assert result["start_context"] == result["end_context"]
+
+    def test_resolve_slice_exact_match(self):
+        text = "line0\nline1\nline2\nline3\nline4\n"
+        slc = FuzzyAnchor.create_slice(text, 2, 4)
+        result = FuzzyAnchor.resolve_slice(text, slc)
+        assert result is not None
+        start, end = result
+        assert start == 2
+        assert end == 4
+
+    def test_resolve_slice_line_inserted_before(self):
+        original = "line0\nline1\nline2\nline3\nline4\n"
+        modified = "NEW\nline0\nline1\nline2\nline3\nline4\n"
+        slc = FuzzyAnchor.create_slice(original, 2, 4)
+        result = FuzzyAnchor.resolve_slice(modified, slc)
+        assert result is not None
+        start, end = result
+        assert start == 3
+        assert end == 5
+
+    def test_resolve_slice_line_deleted_before_returns_none(self):
+        original = "line0\nline1\nline2\nline3\nline4\n"
+        modified = "line0\nline2\nline3\nline4\n"
+        slc = FuzzyAnchor.create_slice(original, 2, 4)
+        result = FuzzyAnchor.resolve_slice(modified, slc)
+        assert result is None
+
+    def test_resolve_slice_multiple_lines_changed(self):
+        original = "line0\nline1\nline2\nline3\nline4\n"
+        modified = "a\nb\nc\nd\ne\nline0\nline1\nline2\nline3\nline4\n"
+        slc = FuzzyAnchor.create_slice(original, 1, 2)
+        result = FuzzyAnchor.resolve_slice(modified, slc)
+        assert result is not None
+        start, end = result
+        assert start == 6
+        assert end == 7
+
+    def test_resolve_slice_anchor_mismatch_returns_none(self):
+        original = "alpha\nbeta\ngamma\ndelta\nepsilon\n"
+        modified = "foo\nbar\nbaz\ndelta\nepsilon\n"
+        slc = FuzzyAnchor.create_slice(original, 2, 3)
+        result = FuzzyAnchor.resolve_slice(modified, slc)
+        assert result is None