perf(javascript): reduce retained semantic analysis allocations (#1601)

Reduce retained semantic allocations and memoize lexical scope ancestry while preserving semantic identities. Refs #1065 and #1563; the complete-directory memory failure remains open.

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

@@ -0,0 +1,43 @@
+import { expect, it, vi } from "vitest";
+
+import { analyzeJavaScriptSemantics } from "./javascriptSemanticAnalysis.js";
+import { onlyBinding } from "./javascriptSemanticAnalysis.fixture.js";
+
+it("bounds ancestry reads for repeated deep lexical references", () => {
+  const ancestryReads = (depth: number): number => {
+    const original = WeakMap.prototype.get;
+    let reads = 0;
+    const get = vi.spyOn(WeakMap.prototype, "get").mockImplementation(function (
+      this: WeakMap<object, unknown>,
+      key,
+    ) {
+      const value: unknown = original.call(this, key);
+      if (
+        typeof value === "object" &&
+        value !== null &&
+        "type" in value &&
+        typeof value.type === "string"
+      )
+        reads++;
+      return value;
+    });
+    try {
+      const ir = analyzeJavaScriptSemantics(
+        `const a=1; module.exports.value=${"a+(".repeat(depth)}a${")".repeat(depth)};`,
+      );
+      expect(ir.coverage).toEqual({ status: "complete", omittedCount: 0 });
+      expect(onlyBinding(ir, "a").value).toEqual({
+        status: "literal",
+        value: 1,
+      });
+      return reads;
+    } finally {
+      get.mockRestore();
+    }
+  };
+
+  const smaller = ancestryReads(80);
+  const larger = ancestryReads(160);
+  expect(smaller).toBeGreaterThan(0);
+  expect(larger).toBeLessThan(3 * smaller);
+});