fix: comment ProverEngine::start() as sync-only

[dwgrantham]

Signed-off-by: Dave Grantham dgrantham@polygon.technology

Description

Fixes audit finding AGLO3.2-22.2. The fix per @Freyskeyd is to add comments marking the ProverEngine::start() function as synchronous-only that can block the async runtime.

Fixes agglayer/security #114

Additions and Changes

Bug fix (non-breaking change which fixes an issue)

Added comments to ProverEngine::start() as well as the callsites.

New feature (non-breaking change which adds functionality)

None

Breaking changes

None

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works

[iljakuklic]

This could be detected at runtime, at least to an extent, with something like:

anyhow::ensure!(
    tokio::runtime::Handle::try_current().is_err(),
    StartingProverInRuntimeError,
);

This will detect whether Tokio runtime is running. It will not detect if a runtime is running in general.

[dwgrantham]

Do we want to try to detect the the Tokio runtime at runtime?