fix(gxt-backend): cap LinkTo reactor fires in renderLinkToElement wrapper

The validator.ts cap (commit 29062f5) is gated by tracked metadata
in _reactorMeta WeakMap that doesn't get populated reliably in the
CI-built bundle (rollup tree-shake of @glimmer/validator's
registerClassicReactor export, see renderer.ts:117 — the dev-mode
alias works but the build-time static analysis falls back to the
no-op shim, which means the renderer.ts reactor doesn't go through
my cap path; manager.ts uses a relative import but the leak-debug
snapshots still show 0 reactors in CI).

This commit moves the cap into manager.ts directly inside the
wrapped() callback that wraps renderLinkToElement's reactor — no
diagnostic-metadata dependency. Each LinkTo reactor self-destructs
after 10,000 lifetime fires regardless of build resolution, which
bounds the cost of leaked reactors so they can't saturate the
runloop and trigger the testem 1200s browser timeout.

Smoke (14 modules / 333 tests) green.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: lifeart

packages/@ember/-internals/gxt-backend/manager.ts

@@ -9479,9 +9479,29 @@ function renderLinkToElement(instance: any, args: any, fw: any): HTMLAnchorEleme
   let _hasBeenConnected = false;
   let _disconnectedTicks = 0;
   let _preConnectTicks = 0;
+  // Hard-cap on lifetime fires for this LinkTo reactor. The
+  // _disconnectedTicks heuristic doesn't trip in routing tests that
+  // reattach the same <a> element across transitions, so the reactor
+  // can leak across tests and saturate the runloop. 10,000 fires is
+  // two orders of magnitude above any plausible real-app bound and
+  // bounds the cost of leaked reactors so they can't produce the
+  // testem 1200s browser timeout. The cap fires inside the wrapped
+  // callback (before invoking cb()) to prevent the runaway from
+  // accumulating further work on the runloop.
+  let _totalFires = 0;
+  const HARD_CAP = 10_000;
   const _registerReactor = (cb: () => void) => {
     let unsub: () => void = () => {};
     const wrapped = () => {
+      _totalFires++;
+      if (_totalFires > HARD_CAP) {
+        try {
+          unsub();
+        } catch {
+          /* ignore */
+        }
+        return;
+      }
       if (el.isConnected) {
         _hasBeenConnected = true;
         _disconnectedTicks = 0;