docs: correct plan's rollback trap design from ERR to EXIT

die() calls exit directly; bash's ERR trap does not fire on an explicit
exit, only when a command's non-zero status propagates through normal
control flow. Verified empirically during Task 4 implementation - switched
to a ROLLBACK_ARMED-guarded EXIT trap, which fires on any shell exit.

docs/superpowers/plans/2026-07-05-native-port-takeover.md

@@ -23,9 +23,11 @@ existing plugin helper library `mysql_common.sh`.
 - Match existing test conventions in `tests/`: plain bash scripts with `fail()`/custom
   asserts, fake command stubs installed via `PATH`/env-var injection, no external test
   framework.
-- Every new/changed script keeps `set -Eeuo pipefail` (the `-E` flag matters here: it's
+- Every new/changed script keeps `set -Eeuo pipefail` and the existing `log()`/`die()`
-  what makes the `ERR` trap fire inside functions, which the rollback design depends on)
+  pattern. The rollback design uses a `trap ... EXIT` (guarded by a `ROLLBACK_ARMED` flag),
-  and the existing `log()`/`die()` pattern.
+  not `trap ... ERR` — `die()` calls `exit` directly, and bash's `ERR` trap does not fire
+  on an explicit `exit`, only on a command's non-zero status propagating through normal
+  control flow. This was verified empirically during Task 4's implementation.
 - Runs only on AlmaLinux 8 or 9 — a stricter, separate check from `install_db.sh`'s own
   permissive `detect_os()`, refusing immediately (before touching anything) on CloudLinux,
   Rocky, CentOS, plain RHEL, or AlmaLinux outside 8/9.
@@ -1057,7 +1059,10 @@ verify_da_connectivity_new_port() {
   log "Potwierdzono łączność DirectAdmina z natywną instancją na porcie $NEW_NATIVE_PORT."
 }
 
+ROLLBACK_ARMED=0
+
 rollback_service_state() {
+  [ "$ROLLBACK_ARMED" -eq 1 ] || return 0
   rollback_config_changes
   restore_custombuild_mysql_management
   if [ -n "$NATIVE_SERVICE_NAME" ]; then
@@ -1086,7 +1091,16 @@ main() {
   preflight_new_port_free
   detect_native_service_name
 
-  trap 'rollback_service_state' ERR
+  # Deliberately an EXIT trap, not an ERR trap. die() (used by every failure
+  # path below) calls `exit` directly, and bash's ERR trap does not fire for
+  # a function that terminates via an explicit `exit` call - it only fires
+  # when a command's non-zero status propagates through normal control flow.
+  # An EXIT trap fires on *any* shell exit (explicit exit, errexit-triggered
+  # exit, or falling off the end of the script), which is what "any failure
+  # from this point on triggers rollback" actually requires. ROLLBACK_ARMED
+  # guards it so it is a no-op before this point and after a successful run.
+  ROLLBACK_ARMED=1
+  trap 'rollback_service_state' EXIT
 
   disable_custombuild_mysql_management
   apply_config_mutations
@@ -1095,7 +1109,8 @@ main() {
   restart_directadmin_service
   verify_da_connectivity_new_port
 
-  trap - ERR
+  ROLLBACK_ARMED=0
+  trap - EXIT
   log "Przejęcie portu natywnej instancji MariaDB zakończone powodzeniem: $NATIVE_CURRENT_PORT -> $NEW_NATIVE_PORT."
 }
 ```