fix(patch): harden V4A patch parser and fuzzy match — 9 correctness bugs

- Bug 1: replace read_file(limit=10000) with read_file_raw in _apply_update,
  preventing silent truncation of files >2000 lines and corruption of lines
  >2000 chars; add read_file_raw to FileOperations abstract interface and
  ShellFileOperations

- Bug 2: split apply_v4a_operations into validate-then-apply phases; if any
  hunk fails validation, zero writes occur (was: continue after failure,
  leaving filesystem partially modified)

- Bug 3: parse_v4a_patch now returns an error for begin-marker-with-no-ops,
  empty file paths, and moves missing a destination (was: always returned
  error=None)

- Bug 4: raise strategy 7 (block anchor) single-candidate similarity threshold
  from 0.10 to 0.50, eliminating false-positive matches in repetitive code

- Bug 5: add _strategy_unicode_normalized (new strategy 7) with position
  mapping via _build_orig_to_norm_map; smart quotes and em-dashes in
  LLM-generated patches now match via strategies 1-6 before falling through
  to fuzzy strategies

- Bug 6: extend fuzzy_find_and_replace to return 4-tuple (content, count,
  error, strategy); update all 5 call sites across patch_parser.py,
  file_operations.py, and skill_manager_tool.py

- Bug 7: guard in _apply_update returns error when addition-only context hint
  is ambiguous (>1 occurrences); validation phase errors on both 0 and >1

- Bug 8: _apply_delete returns error (not silent success) on missing file

- Bug 9: _validate_operations checks source existence and destination absence
  for MOVE operations before any write occurs

tests/tools/test_patch_parser.py

@@ -159,7 +159,7 @@ class TestApplyUpdate:
             def __init__(self):
                 self.written = None
 
-            def read_file(self, path, offset=1, limit=500):
+            def read_file_raw(self, path):
                 return SimpleNamespace(
                     content=(
                         'def run():\n'
@@ -211,7 +211,7 @@ class TestAdditionOnlyHunks:
         # Apply to a file that contains the context hint
         class FakeFileOps:
             written = None
-            def read_file(self, path, **kw):
+            def read_file_raw(self, path):
                 return SimpleNamespace(
                     content="def main():\n    pass\n",
                     error=None,
@@ -239,7 +239,7 @@ class TestAdditionOnlyHunks:
 
         class FakeFileOps:
             written = None
-            def read_file(self, path, **kw):
+            def read_file_raw(self, path):
                 return SimpleNamespace(
                     content="existing = True\n",
                     error=None,
@@ -253,3 +253,259 @@ class TestAdditionOnlyHunks:
         assert result.success is True
         assert file_ops.written.endswith("def new_func():\n    return True\n")
         assert "existing = True" in file_ops.written
+
+
+class TestReadFileRaw:
+    """Bug 1 regression tests — files > 2000 lines and lines > 2000 chars."""
+
+    def test_apply_update_file_over_2000_lines(self):
+        """A hunk targeting line 2200 must not truncate the file to 2000 lines."""
+        patch = """\
+*** Begin Patch
+*** Update File: big.py
+@@ marker_at_2200 @@
+ line_2200
+-old_value
++new_value
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        # Build a 2500-line file; the hunk targets a region at line 2200
+        lines = [f"line_{i}" for i in range(1, 2501)]
+        lines[2199] = "line_2200"   # index 2199 = line 2200
+        lines[2200] = "old_value"
+        file_content = "\n".join(lines)
+
+        class FakeFileOps:
+            written = None
+            def read_file_raw(self, path):
+                return SimpleNamespace(content=file_content, error=None)
+            def write_file(self, path, content):
+                self.written = content
+                return SimpleNamespace(error=None)
+
+        file_ops = FakeFileOps()
+        result = apply_v4a_operations(ops, file_ops)
+        assert result.success is True
+        written_lines = file_ops.written.split("\n")
+        assert len(written_lines) == 2500, (
+            f"Expected 2500 lines, got {len(written_lines)}"
+        )
+        assert "new_value" in file_ops.written
+        assert "old_value" not in file_ops.written
+
+    def test_apply_update_preserves_long_lines(self):
+        """A line > 2000 chars must be preserved verbatim after an unrelated hunk."""
+        long_line = "x" * 3000
+        patch = """\
+*** Begin Patch
+*** Update File: wide.py
+@@ short_func @@
+ def short_func():
+-    return 1
++    return 2
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        file_content = f"def short_func():\n    return 1\n{long_line}\n"
+
+        class FakeFileOps:
+            written = None
+            def read_file_raw(self, path):
+                return SimpleNamespace(content=file_content, error=None)
+            def write_file(self, path, content):
+                self.written = content
+                return SimpleNamespace(error=None)
+
+        file_ops = FakeFileOps()
+        result = apply_v4a_operations(ops, file_ops)
+        assert result.success is True
+        assert long_line in file_ops.written, "Long line was truncated"
+        assert "... [truncated]" not in file_ops.written
+
+
+class TestValidationPhase:
+    """Bug 2 regression tests — validation prevents partial apply."""
+
+    def test_validation_failure_writes_nothing(self):
+        """If one hunk is invalid, no files should be written."""
+        patch = """\
+*** Begin Patch
+*** Update File: a.py
+ def good():
+-    return 1
++    return 2
+*** Update File: b.py
+ THIS LINE DOES NOT EXIST
+-    old
++    new
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        written = {}
+
+        class FakeFileOps:
+            def read_file_raw(self, path):
+                files = {
+                    "a.py": "def good():\n    return 1\n",
+                    "b.py": "completely different content\n",
+                }
+                content = files.get(path)
+                if content is None:
+                    return SimpleNamespace(content=None, error=f"File not found: {path}")
+                return SimpleNamespace(content=content, error=None)
+
+            def write_file(self, path, content):
+                written[path] = content
+                return SimpleNamespace(error=None)
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+        assert result.success is False
+        assert written == {}, f"No files should have been written, got: {list(written.keys())}"
+        assert "validation failed" in result.error.lower()
+
+    def test_all_valid_operations_applied(self):
+        """When all operations are valid, all files are written."""
+        patch = """\
+*** Begin Patch
+*** Update File: a.py
+ def foo():
+-    return 1
++    return 2
+*** Update File: b.py
+ def bar():
+-    pass
++    return True
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        written = {}
+
+        class FakeFileOps:
+            def read_file_raw(self, path):
+                files = {
+                    "a.py": "def foo():\n    return 1\n",
+                    "b.py": "def bar():\n    pass\n",
+                }
+                return SimpleNamespace(content=files[path], error=None)
+
+            def write_file(self, path, content):
+                written[path] = content
+                return SimpleNamespace(error=None)
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+        assert result.success is True
+        assert set(written.keys()) == {"a.py", "b.py"}
+
+
+class TestApplyDelete:
+    """Tests for _apply_delete producing a real unified diff."""
+
+    def test_delete_diff_contains_removed_lines(self):
+        """_apply_delete must embed the actual file content in the diff, not a placeholder."""
+        patch = """\
+*** Begin Patch
+*** Delete File: old/stuff.py
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        class FakeFileOps:
+            deleted = False
+
+            def read_file_raw(self, path):
+                return SimpleNamespace(
+                    content="def old_func():\n    return 42\n",
+                    error=None,
+                )
+
+            def delete_file(self, path):
+                self.deleted = True
+                return SimpleNamespace(error=None)
+
+        file_ops = FakeFileOps()
+        result = apply_v4a_operations(ops, file_ops)
+
+        assert result.success is True
+        assert file_ops.deleted is True
+        # Diff must contain the actual removed lines, not a bare comment
+        assert "-def old_func():" in result.diff
+        assert "-    return 42" in result.diff
+        assert "/dev/null" in result.diff
+
+    def test_delete_diff_fallback_on_empty_file(self):
+        """An empty file should produce the fallback comment diff."""
+        patch = """\
+*** Begin Patch
+*** Delete File: empty.py
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+
+        class FakeFileOps:
+            def read_file_raw(self, path):
+                return SimpleNamespace(content="", error=None)
+
+            def delete_file(self, path):
+                return SimpleNamespace(error=None)
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+        assert result.success is True
+        # unified_diff produces nothing for two empty inputs — fallback comment expected
+        assert "Deleted" in result.diff or result.diff.strip() == ""
+
+
+class TestCountOccurrences:
+    def test_basic(self):
+        from tools.patch_parser import _count_occurrences
+        assert _count_occurrences("aaa", "a") == 3
+        assert _count_occurrences("aaa", "aa") == 2
+        assert _count_occurrences("hello world", "xyz") == 0
+        assert _count_occurrences("", "x") == 0
+
+
+class TestParseErrorSignalling:
+    """Bug 3 regression tests — parse_v4a_patch must signal errors, not swallow them."""
+
+    def test_update_with_no_hunks_returns_error(self):
+        """An UPDATE with no hunk lines is a malformed patch and should error."""
+        patch = """\
+*** Begin Patch
+*** Update File: foo.py
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is not None, "Expected a parse error for hunk-less UPDATE"
+        assert ops == []
+
+    def test_move_without_destination_returns_error(self):
+        """A MOVE without '->' syntax should not silently produce a broken operation."""
+        # The move regex requires '->' so this will be treated as an unrecognised
+        # line and the op is never created.  Confirm nothing crashes and ops is empty.
+        patch = """\
+*** Begin Patch
+*** Move File: src/foo.py
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        # Either parse sees zero ops (fine) or returns an error (also fine).
+        # What is NOT acceptable is ops=[MOVE op with empty new_path] + err=None.
+        if ops:
+            assert err is not None, (
+                "MOVE with missing destination must either produce empty ops or an error"
+            )
+
+    def test_valid_patch_returns_no_error(self):
+        """A well-formed patch must still return err=None."""
+        patch = """\
+*** Begin Patch
+*** Update File: f.py
+ ctx
+-old
++new
+*** End Patch"""
+        ops, err = parse_v4a_patch(patch)
+        assert err is None
+        assert len(ops) == 1