diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 551e266..0804ae2 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -39,3 +39,8 @@
 **Vulnerability:** Use of predictable, hardcoded temporary file paths and extraction directories in a shared `/tmp` directory.
 **Learning:** Using hardcoded paths for temporary files or directories (such as `TMP` and `EXTRACT_DIR` inside `/tmp` or `${PREFIX}/tmp`) makes the script vulnerable to symlink attacks, arbitrary file overwriting, and race conditions (CWE-377, CWE-59) by other local users on a shared system.
 **Prevention:** Always use `mktemp -d` to securely create a unique temporary directory with restricted `0700` permissions (readable/writable only by the owner), and place all temporary files and extraction directories within it.
+
+## 2026-07-31 - Environment Variable Hijacking and Arbitrary File Destruction via Trap Cleanup Logic
+**Vulnerability:** Uninitialized critical variables in shell scripts (e.g., `ANTIGRAVITY_BAK`, `INSTALL_BIN_DIR`) can be hijacked from the parent environment, allowing users/attackers to manipulate execution flows. When coupled with script-level cleanup traps (like moving or deleting backup files on exit/cancel), uninitialized environment variables can lead to arbitrary file move or deletion operations (CWE-377, CWE-59, CWE-459).
+**Learning:** Trap handlers in shell scripts run on any exit or cancellation. If the script fails or exits before variables are initialized inside the script body, pre-existing environment variables of the same name can control file operations inside the trap handler.
+**Prevention:** Always explicitly initialize critical shell variables controlling backup paths, installation folders, or temporary locations at the very beginning of the script body. Additionally, validate that target variables are non-empty before executing state-altering commands like `mv` or `rm`.
diff --git a/install.sh b/install.sh
index 17c4fea..fcb46ef 100644
--- a/install.sh
+++ b/install.sh
@@ -2,6 +2,14 @@
 # Antigravity CLI - Termux Native (Setup)
 set -Eeuo pipefail
 
+# Security Enhancement (Sentinel): Initialize critical variables to prevent environment hijacking
+# and arbitrary file deletion/move vulnerabilities (CWE-377, CWE-59, CWE-459).
+ANTIGRAVITY_BAK=""
+ANTIGRAVITY_VA39_BAK=""
+INSTALL_BIN_DIR=""
+SECURE_TMP_DIR=""
+INSTALL_SUCCESS=0
+
 REPO="${ANTIGRAVITY_REPO:-wallentx/antigravity-cli-termux}"
 if [[ "$REPO" == -* || "$REPO" == *[!a-zA-Z0-9_./-]* ]]; then
   printf "[ERR] Invalid ANTIGRAVITY_REPO: contains unsafe characters or starts with a dash\n" >&2
@@ -62,12 +70,12 @@ mkdir -p "$SECURE_TMP_DIR" 2>/dev/null || true
 # ── Cleanup Hook ──────────────────────────────────────────────────────────────
 cleanup() {
   printf "\033[?25h" # Restore cursor if cancelled
-  [[ -d "$SECURE_TMP_DIR" ]] && rm -rf "$SECURE_TMP_DIR"
+  [[ -n "${SECURE_TMP_DIR:-}" && -d "$SECURE_TMP_DIR" ]] && rm -rf "$SECURE_TMP_DIR"
   if [[ "${INSTALL_SUCCESS:-0}" -ne 1 ]]; then
-    if [[ -n "${ANTIGRAVITY_BAK:-}" && -f "$ANTIGRAVITY_BAK" ]]; then
+    if [[ -n "${INSTALL_BIN_DIR:-}" && -n "${ANTIGRAVITY_BAK:-}" && -f "$ANTIGRAVITY_BAK" ]]; then
       mv -f "$ANTIGRAVITY_BAK" "$INSTALL_BIN_DIR/antigravity" || true
     fi
-    if [[ -n "${ANTIGRAVITY_VA39_BAK:-}" && -f "$ANTIGRAVITY_VA39_BAK" ]]; then
+    if [[ -n "${INSTALL_BIN_DIR:-}" && -n "${ANTIGRAVITY_VA39_BAK:-}" && -f "$ANTIGRAVITY_VA39_BAK" ]]; then
       mv -f "$ANTIGRAVITY_VA39_BAK" "$INSTALL_BIN_DIR/antigravity.va39" || true
     fi
   else