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

Low Risk
Changes are limited to process lifecycle, logging, and shutdown paths; no proving logic, RPC semantics, or auth/data handling are modified.

Overview
Adds operational hardening for the transaction prover binary: panics and container shutdowns show up as structured logs instead of ad-hoc stderr output.

A new install_panic_hook runs after tracing is initialized and emits a single event=panic error! with message, source location, and backtrace (abort behavior unchanged). tracing-subscriber gains the json feature to support existing JSON log format.

SIGTERM and SIGINT are wired to ServerHandle::stop with shutdown_started / shutdown_complete log events so orchestrator teardown is visible and in-flight work can drain. Handler install failures are warned but partial handlers still run. A second termination signal triggers force_exit and exit(1) so a stuck graceful shutdown cannot trap the process (Tokio signal quirk). tokio adds the signal feature for Unix signal streams.

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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: document observability surface in README #14203
• 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,tower_ohttp: OHTTP-unlinkable request-id for decapsulated content #14222
• starknet_transaction_prover: per-request structured log with request-id #14165
• starknet_transaction_prover: unify HTTP middleware stack via macro #14286
• main-v0.14.3

This stack of pull requests is managed by Graphite. Learn more about stacking.

[reviewable-StarkWare]

This change is 

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Reimplements already-stable standard library method

Low Severity

The extract_payload function manually reimplements PanicHookInfo::payload_as_str(), which was stabilized in Rust 1.91.0. The project's rust-toolchain.toml specifies channel 1.95, so the standard library method is already available. The doc comment on extract_payload references a nightly-2025-07-14 toolchain that no longer matches the project's actual pinned toolchain, making the stated reason for the workaround stale.

 

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[avi-starkware]

Actually, the crate starknet_transaction_prover uses the referenced nightly toolchain, so the doc comment is not stale