test: smoke scripts fail when they stop before their last check

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/Integration/lib.sh

@@ -20,6 +20,20 @@ INIT_RESPONSE=""
 REQUEST_ID=100
 
 fail() { echo "FAIL: $*"; exit 1; }
+
+# A smoke script must reach its last line: finish() marks that and prints the verdict.
+# guard_exit (called first in every EXIT trap) turns any other exit – including a silent
+# stop that still returns 0 – into a failure, so a run can never pass without all checks.
+SMOKE_FINISHED=0
+finish() { SMOKE_FINISHED=1; echo "ALL CHECKS PASSED"; }
+guard_exit() {
+  local rc=$1
+  if [ "$rc" -eq 0 ] && [ "$SMOKE_FINISHED" != 1 ]; then
+    echo "FAIL: script stopped before its last check (exit 0 without finish)"
+    return 1
+  fi
+  return "$rc"
+}
 pass() { echo "ok   - $*"; }
 
 # Removes every "lit-mcp-integration-test" application password of a user.