fix(python): preserve historical signed code fields

Keep signed co_stacksize and co_flags for historical magic entries whose constructors accepted them. Preserve magic 3410 with a constructor-revision limitation; reject negative values from 3411 onward.

Fixes #6487

src/python/PythonPycParser.test.ts

@@ -1520,9 +1520,12 @@ it("rejects code CPython treats as corrupt instead of complete coverage", () =>
   expect(() => parse(file("py311", 3531, { flags: 0x80000000 }))).toThrow(
     /co_flags is negative/,
   );
-  expect(() => parse(file("py37", 3401, { flags: 0x80000000 }))).toThrow(
+  expect(() => parse(file("py38", 3411, { flags: 0x80000000 }))).toThrow(
     /co_flags is negative/,
   );
+  expect(() => parse(file("py38", 3411, { stacksize: 0xffffffff }))).toThrow(
+    /co_stacksize is negative/,
+  );
 
   const valid = parse(
     file("py311", 3531, {
@@ -1544,6 +1547,25 @@ it("rejects code CPython treats as corrupt instead of complete coverage", () =>
   const negativePy37Flags = parse(file("py37", 3394, { flags: 0x80000000 }));
   expect(root(negativePy37Flags).flags).toBe(-0x80000000);
   expect(pythonPycSchema.safeParse(negativePy37Flags).success).toBe(true);
+  const negativePy37Stacksize = parse(
+    file("py37", 3394, { stacksize: 0xffffffff }),
+  );
+  expect(root(negativePy37Stacksize).stacksize).toBe(-1);
+  expect(pythonPycSchema.safeParse(negativePy37Stacksize).success).toBe(true);
+  const negativePy38AlphaFlags = parse(
+    file("py37", 3401, { flags: 0x80000000 }),
+  );
+  expect(root(negativePy38AlphaFlags).flags).toBe(-0x80000000);
+  const ambiguousPy38Fields = parse(
+    file("py38", 3410, { stacksize: 0xffffffff, flags: 0x80000000 }),
+  );
+  expect(root(ambiguousPy38Fields)).toMatchObject({
+    stacksize: -1,
+    flags: -0x80000000,
+  });
+  expect(ambiguousPy38Fields.limitations).toEqual(
+    expect.arrayContaining([expect.stringContaining("Magic 3410 is shared")]),
+  );
   const py37 = parse(
     file("py37", 3394, {
       argcount: 1,