chore: import upstream snapshot with attribution

tests/test_tools/test_source_edit_contract.py

@@ -0,0 +1,73 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from opensquilla.tools.source_edit_contract import (
+    SourceEditContractError,
+    apply_line_edits,
+    build_diff_summary,
+    build_line_receipt,
+    source_revision_for_path,
+)
+
+
+def test_source_revision_changes_when_file_content_changes(tmp_path: Path) -> None:
+    path = tmp_path / "src.py"
+    path.write_text("alpha\n", encoding="utf-8")
+    first = source_revision_for_path(path)
+
+    path.write_text("beta\n", encoding="utf-8")
+    second = source_revision_for_path(path)
+
+    assert first.startswith("file_")
+    assert second.startswith("file_")
+    assert first != second
+
+
+def test_build_line_receipt_returns_plain_lines_without_read_file_prefixes(
+    tmp_path: Path,
+) -> None:
+    path = tmp_path / "src.py"
+    path.write_text("one\ntwo\nthree\n", encoding="utf-8")
+
+    receipt = build_line_receipt(path, start_line=2, end_line=3, display_path="src.py")
+
+    assert receipt["status"] == "success"
+    assert receipt["path"] == "src.py"
+    assert receipt["range"] == [2, 3]
+    assert receipt["lines"] == [
+        {"line": 2, "text": "two"},
+        {"line": 3, "text": "three"},
+    ]
+    assert receipt["revision"].startswith("file_")
+
+
+def test_apply_line_edits_replaces_inclusive_ranges_atomically() -> None:
+    original = "a\nb\nc\nd\n"
+
+    updated = apply_line_edits(
+        original,
+        [{"start_line": 2, "end_line": 3, "replacement": "B\nC\n"}],
+    )
+
+    assert updated == "a\nB\nC\nd\n"
+
+
+def test_apply_line_edits_rejects_overlapping_ranges() -> None:
+    with pytest.raises(SourceEditContractError, match="overlap"):
+        apply_line_edits(
+            "a\nb\nc\n",
+            [
+                {"start_line": 1, "end_line": 2, "replacement": "x\n"},
+                {"start_line": 2, "end_line": 3, "replacement": "y\n"},
+            ],
+        )
+
+
+def test_build_diff_summary_uses_readable_unified_diff_headers() -> None:
+    summary = build_diff_summary("a\nb\n", "a\nB\n", path="src/app.py")
+
+    assert summary.startswith("--- a/src/app.py\n+++ b/src/app.py\n@@")
+    assert "\n-b\n+B\n" in summary