feat: runtime-aware tmux agent checks

internal/tmux/tmux_test.go

@@ -260,6 +260,11 @@ func TestEnsureSessionFresh_ZombieSession(t *testing.T) {
 		t.Skip("session unexpectedly has Claude running - can't test zombie case")
 	}
 
+	// Verify generic agent check also treats it as not running (shell session)
+	if tm.IsAgentRunning(sessionName) {
+		t.Fatalf("expected IsAgentRunning(%q) to be false for a fresh shell session", sessionName)
+	}
+
 	// EnsureSessionFresh should kill the zombie and create fresh session
 	// This should NOT error with "session already exists"
 	if err := tm.EnsureSessionFresh(sessionName, ""); err != nil {