fix(kafka): fail closed when listing topics for an all-topics backup

In the empty-TOPICS (back up all non-internal topics) branch, the topic
list was resolved with a single pipeline under set -eu without pipefail:

  TLIST=$(kafka-topics.sh --list | grep -v '^_' || true)

The pipeline's exit status is grep's alone, so a real broker error
(unreachable / auth) that emits no stdout makes grep exit 1, || true swallows
it, and TLIST is empty - indistinguishable from 'no non-internal topics'. The
backup then drains nothing, tars an empty dir, PUTs it and reports success: a
silent empty backup a later restore would treat as authoritative.

Split the --list into its own command substitution so a broker error aborts
the Pod under set -e; filter internal topics only afterwards, so an empty
TLIST means genuinely no user topics.

Signed-off-by: Andrey Kolkov <andrey.kolkov@aenix.io>
Assisted-by: LLM

examples/backups/kafka/01-create-strategy.sh

@@ -156,7 +156,15 @@ spec:
                 if [ -n "\${TOPICS}" ]; then
                   TLIST=\$(printf '%s' "\${TOPICS}" | tr ', ' '  ')
                 else
-                  TLIST=\$("\${BIN}"/kafka-topics.sh --bootstrap-server "\${BOOT}" --list | grep -v '^_' || true)
+                  # Fail closed: run --list as its own command so a broker
+                  # error (unreachable / auth) aborts the Pod under set -e
+                  # instead of the pipe masking the exit status to grep's and
+                  # || true swallowing it. Only then filter internal topics, so
+                  # an empty TLIST means genuinely no non-internal topics -
+                  # never a silently swallowed failure that would PUT an empty
+                  # tarball and report success.
+                  raw=\$("\${BIN}"/kafka-topics.sh --bootstrap-server "\${BOOT}" --list)
+                  TLIST=\$(printf '%s\n' "\${raw}" | grep -v '^_' || true)
                 fi
                 echo "backing up topics [\${TLIST}] from \${BOOT}"
                 MANIFEST="\${WORK}/manifest.txt"