[core-be-agent] fix vet warnings: unused variables in hub_test and bundle_helpers_test

Per QA review of PR #794:

1. hub_test.go TestNewHub_WithAccessChecker: `called` was set but never
   read (unused variable → go vet failure). Added assertion that checks
   `called` is true after verifying the access checker was invoked.

2. bundle_helpers_test.go TestSplitLines_Empty: `want` was declared as
   []string{""} but only len(want) was used — the actual content was
   never compared. Fixed to assert len(got)==1 && got[0]=="", which
   validates the correct split behavior for an empty string.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/bundle/bundle_helpers_test.go

@@ -45,9 +45,9 @@ func TestSplitLines_TrailingNewline(t *testing.T) {
 
 func TestSplitLines_Empty(t *testing.T) {
 	got := splitLines("")
-	want := []string{""}
-	if len(got) != len(want) {
-		t.Errorf("empty string should produce one empty-string element; got %v", got)
+	// An empty string should return a single-element slice containing ""
+	if len(got) != 1 || got[0] != "" {
+		t.Errorf("empty string should produce one empty-string element; got %v (len=%d)", got, len(got))
 	}
 }
 

workspace-server/internal/ws/hub_test.go

@@ -50,6 +50,10 @@ func TestNewHub_WithAccessChecker(t *testing.T) {
 	if h.canCommunicate("ws-1", "ws-2") {
 		t.Error("canCommunicate should return false for different IDs")
 	}
+	// Verify the checker was invoked at least once
+	if !called {
+		t.Error("access checker was not called")
+	}
 }
 
 // ---------- safeSend ----------