fix(gxt-backend): raise cumulative foreign-fire cap to 1500

CI evidence on commit a42b371: cumulative cap at 200 caught the
hang (Basic Test 13min instead of 41min) but regressed 700+ tests
in the load-bearing-leak cluster. The cap was firing on legitimate
cross-test reactor activity (Ember test infrastructure propagates
some dirties across tests for shared setup chains).

Move the cap above the observed leak signature peak (1140 lifetime
fires per leaked reactor in CI) but still bounded so an unbounded
runaway can't saturate the runloop indefinitely. 1500 leaves room
for shared-setup chains without leaving unbounded-leak headroom.

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

Author: lifeart

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

@@ -728,11 +728,13 @@ const REACTOR_FOREIGN_FIRE_CAP = 100;
 // Cap on CUMULATIVE fires across all foreign tests (never resets).
 // Catches slow leaks where fires are spread across many tests but
 // never concentrate enough in any one. CI evidence: leaked reactors
-// fire ~50 times per foreign test (under the per-test cap) but
-// totalForeignFires reaches 1000+ across the run. 200 catches this
-// well above any plausible legitimate cross-test reactivity (real
-// reactors don't fire across foreign tests at all).
-const REACTOR_TOTAL_FOREIGN_FIRE_CAP = 200;
+// fire ~50 times per foreign test, accumulating 1000-1140 lifetime
+// fires before timeout. 1500 sits above the observed peak so
+// legitimate cross-test reactor activity (some Ember test
+// infrastructure does propagate dirties across tests for shared
+// setup) isn't culled, while still bounding the unbounded-runaway
+// case where leaked reactors would fire indefinitely.
+const REACTOR_TOTAL_FOREIGN_FIRE_CAP = 1500;
 const NO_TEST_SENTINEL = '<no-test>';
 
 function _fireClassicReactors() {