starknet_transaction_prover: global panic hook + graceful SIGTERM shutdown

[avi-starkware]

Installs a process-wide panic hook that emits one structured event=panic
tracing event with location and backtrace, and bridges SIGTERM/SIGINT into
ServerHandle::stop so container teardown becomes visible in logs and
in-flight proofs get to finish. A second signal forces exit(1) to work
around tokio-rs/tokio#7905.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

[cursor]

PR Summary

Medium Risk
Changes long-running process lifecycle (signal handling and forced exit) for the proving server; low security impact but affects production teardown and incident visibility.

Overview
Improves operability of the Starknet transaction prover binary: panics and container shutdown now show up as structured logs instead of ad-hoc stderr output.

After tracing is initialized, the process installs a global panic hook that logs a single event=panic error with message, source location, and a forced backtrace (without changing default abort-on-panic behavior). Dependencies gain tracing-subscriber’s json feature so this lines up with existing JSON log format.

SIGTERM and SIGINT are wired into jsonrpsee’s ServerHandle::stop, with shutdown_started / shutdown_complete (and warnings on stop failures). Handler registration is best-effort per signal; a second termination signal triggers force_exit and exit(1) so operators can escape a stuck graceful shutdown (documented Tokio signal quirk).

Unit tests cover panic payload extraction for common panic! forms.

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[avi-starkware]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• starknet_transaction_prover: origin-level breadcrumbs for validation errors #14172
• starknet_transaction_prover: /health returns 503 when service is saturated #14171
• starknet_transaction_prover: bump prover_panics_total on panic hook fire #14170
• starknet_transaction_prover: HTTP request count + latency + in-flight metrics #14169
• starknet_transaction_prover: proving-job duration + outcome metrics #14168
• starknet_transaction_prover: Prometheus /metrics endpoint with build_info #14167
• starknet_transaction_prover: global panic hook + graceful SIGTERM shutdown #14166 👈 (View in Graphite)
• starknet_transaction_prover: per-request structured log with request-id #14165
• starknet_transaction_prover: redact URL credentials in logs and add startup banner #14164
• starknet_transaction_prover: add /health endpoint via HealthLayer #14163
• starknet_transaction_prover: add --log-format text|json CLI flag #14162
• main

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[reviewable-StarkWare]

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