fix(javascript): avoid positive-zero evidence for signed zero

src/domain/javascript/javascriptSemanticAnalysis.signed_zero.test.ts

@@ -0,0 +1,35 @@
+import { expect, it } from "vitest";
+
+import { analyzeJavaScriptSemantics } from "./javascriptSemanticAnalysis.js";
+import { topLevelBinding } from "./javascriptSemanticAnalysis.fixture.js";
+import { semanticPrimitiveSet } from "./javascriptSemanticPrimitives.js";
+
+it.each(["-0", "-0.0", "-0x0", "-0 * 5", "-1 * 0", '+"-0"'])(
+  "does not publish positive zero evidence for %s",
+  (expression) => {
+    const ir = analyzeJavaScriptSemantics(
+      `export const value = ${expression};`,
+    );
+    expect(topLevelBinding(ir, "value").value).toMatchObject({
+      status: "unknown",
+    });
+  },
+);
+
+it("does not collapse a possible negative-zero branch into positive-zero certainty", () => {
+  const ir = analyzeJavaScriptSemantics("const value = choice ? -0 : 0;");
+  expect(topLevelBinding(ir, "value").value.status).not.toBe("literal");
+  expect(semanticPrimitiveSet([-0, 0])).toMatchObject({ status: "unknown" });
+});
+
+it.each([
+  { expression: "0", value: 0 },
+  { expression: "-1", value: -1 },
+  { expression: '"-0"', value: "-0" },
+])("preserves representable primitive $expression", ({ expression, value }) => {
+  const ir = analyzeJavaScriptSemantics(`const value = ${expression};`);
+  expect(topLevelBinding(ir, "value").value).toEqual({
+    status: "literal",
+    value,
+  });
+});