#275 handle SIGTERM with graceful shutdown in entry.sh

[VasilevNStas]

When the orchestrator (Docker, container scheduler, or manual cancel) sends SIGTERM to the container, entry.sh currently has no signal handler. The process is killed immediately — stdout is lost, and baza.rb cannot distinguish between "job was cancelled" and "job disappeared due to infrastructure failure".

The problem

# Before: SIGTERM arrives → silent death, no output
kill -TERM <entry.sh-pid>
# → nothing in stdout, baza.rb sees mystery disappearance

What this PR adds

trap cleanup SIGTERM

cleanup() {
  elapsed=$(($(date +%s) - start_time))
  echo "Job ${id} terminated after ${elapsed}s"
  exit 143
}

Scenario	Before	After
SIGTERM during job	Silent death, no output	"Job X terminated after Ys" + exit 143
Normal completion	exit 0	exit 0 (unchanged)
baza.rb polling	Sees "job disappeared"	Sees finished? == yes, exit_code == 143

Why exit 143?

Exit code 143 = 128 + 15 (SIGTERM). This is the POSIX shell convention: when a process is killed by signal N, the shell reports exit code 128+N. Using 143 allows baza.rb (or any caller) to distinguish:

• 143: terminated by SIGTERM (intentional cancel)
• 1-127: normal error (judge logic failure, missing files, etc.)
• 0: success

Signal flow

1. Orchestrator sends SIGTERM → entry.sh trap fires
2. cleanup() prints diagnostic and calls exit 143
3. Script terminates, child processes inherit signal handling cleanup

Docker, Kubernetes, and most container runtimes send SIGTERM first, then SIGKILL after a grace period. This trap handles the graceful phase.

Checklist

• bundle exec rubocop — 0 offenses
• bundle exec rake — all tasks pass
• HoC ≤ 133

@yegor256 please review

[VasilevNStas]

@yegor256 — this PR is part of a 3-PR series that addresses a critical reliability gap in the baza.rb ↔ entry.sh pipeline.

The problem: When baza.rb pushes a job, entry.sh runs judges update with no time limit, no convergence detection, and no signal handling. If judges hang or fail to converge, the container runs forever and baza.rb's polling of finished? times out after 10 minutes with no diagnostic information — the user sees a silent failure.