chore: import upstream snapshot with attribution

internal/plugin/codegraph_limit_test.go

@@ -0,0 +1,46 @@
+package plugin
+
+import "testing"
+
+func TestAcquireCodeGraphSlotCapsInstances(t *testing.T) {
+	// Drain any residual count from parallel tests by asserting a clean start.
+	if got := liveCodeGraphInstances.Load(); got != 0 {
+		t.Fatalf("expected 0 live instances at start, got %d", got)
+	}
+
+	releases := make([]func(), 0, maxCodeGraphInstances)
+	for i := 0; i < maxCodeGraphInstances; i++ {
+		release, err := acquireCodeGraphSlot()
+		if err != nil {
+			t.Fatalf("acquire %d within cap should succeed: %v", i, err)
+		}
+		releases = append(releases, release)
+	}
+
+	// One past the cap must be refused, and the counter must not leak upward.
+	if _, err := acquireCodeGraphSlot(); err == nil {
+		t.Fatal("acquiring past the cap should fail")
+	}
+	if got := liveCodeGraphInstances.Load(); got != int32(maxCodeGraphInstances) {
+		t.Fatalf("count must stay at cap after a refused acquire, got %d", got)
+	}
+
+	// Releasing frees a slot, and release is idempotent.
+	releases[0]()
+	releases[0]()
+	if got := liveCodeGraphInstances.Load(); got != int32(maxCodeGraphInstances-1) {
+		t.Fatalf("double-release must free exactly one slot, got %d", got)
+	}
+	release, err := acquireCodeGraphSlot()
+	if err != nil {
+		t.Fatalf("a freed slot should be reusable: %v", err)
+	}
+	releases[0] = release
+
+	for _, r := range releases {
+		r()
+	}
+	if got := liveCodeGraphInstances.Load(); got != 0 {
+		t.Fatalf("all slots must be freed at end, got %d", got)
+	}
+}