fix(quality): restore 100% python branch coverage on protected main

scripts/check_coverage.py

@@ -37,45 +37,6 @@ def load_totals(path: Path) -> Mapping[str, Any]:
     return merged
 
 
-def load_union_branch_totals(files: Sequence[object]) -> Mapping[str, int | float]:
-    """Merge LLVM branch outcomes by source coordinate across test binaries."""
-
-    outcomes: dict[tuple[str, int, int, int, int], list[int]] = {}
-    for file_record in files:
-        if not isinstance(file_record, Mapping):
-            raise ValueError("coverage file record must be an object")
-        filename = file_record.get("filename")
-        if "branches" not in file_record:
-            raise ValueError("coverage file record must contain branches")
-        branches = file_record["branches"]
-        if not isinstance(filename, str) or not filename:
-            raise ValueError("coverage file record must contain a filename")
-        if not isinstance(branches, list):
-            raise ValueError("coverage branches must be a list")
-        for branch in branches:
-            if not isinstance(branch, list) or len(branch) < 6:
-                raise ValueError("coverage branch record is malformed")
-            coordinates = branch[:4]
-            counts = branch[4:6]
-            if not all(
-                isinstance(value, int) and not isinstance(value, bool) and value >= 0
-                for value in coordinates
-            ):
-                raise ValueError("coverage branch coordinates are invalid")
-            if not all(
-                isinstance(value, int) and not isinstance(value, bool) and value >= 0
-                for value in counts
-            ):
-                raise ValueError("coverage branch counts are invalid")
-            key = (filename, *coordinates)
-            outcome = outcomes.setdefault(key, [0, 0])
-            outcome[0] += counts[0]
-            outcome[1] += counts[1]
-    count = len(outcomes) * 2
-    covered = sum(outcome > 0 for counts in outcomes.values() for outcome in counts)
-    return {"count": count, "covered": covered}
-
-
 def _parse_branch_record(record: object) -> tuple[tuple[int, int, int, int], int, int]:
     """Return ``(site, true_count, false_count)`` from one LLVM branch tuple.
 

tests/quality/test_check_coverage.py

@@ -790,6 +790,48 @@ def test_multiline_scanner_ignores_comments_char_literals_and_raw_strings(self)
 
 
 
+    def test_union_branch_totals_merge_counts_across_binaries(self) -> None:
+        """Valid records sum per coordinate across duplicate instrumented copies."""
+
+        files = [
+            {
+                "filename": "src/lib.rs",
+                "branches": [
+                    [10, 1, 5, 6, 3, 0],
+                    [20, 2, 7, 8, 0, 4],
+                ],
+            },
+            {
+                "filename": "src/lib.rs",
+                "branches": [
+                    [10, 1, 5, 6, 1, 2],
+                ],
+            },
+        ]
+        self.assertEqual(
+            coverage_contract.load_union_branch_totals(files),
+            {"count": 4, "covered": 3},
+        )
+
+    def test_blank_history_comma_scan_exhaustion(self) -> None:
+        """Blank-only preceding lines exhaust the reverse scan and stay unproven."""
+
+        lines = ["", "   ", "    ,"]
+        self.assertFalse(
+            coverage_contract._is_structural_comma_continuation(lines, 3, ",")
+        )
+
+    def test_char_literal_with_escaped_backslash_keeps_scanner_exact(self) -> None:
+        """An escaped-backslash char literal cannot flip the multiline verdict."""
+
+        lines = [
+            "const slash: char = '\\\\';",
+            'static tail: &str = "open',
+            '    tail";',
+        ]
+        self.assertTrue(coverage_contract._line_in_multiline_string(lines, 3))
+        self.assertFalse(coverage_contract._line_in_multiline_string(lines, 2))
+
     def test_multiline_string_empty_lines_returns_false(self) -> None:
         """An empty source produces no multiline-string continuations."""