starknet_os_runner: prove CairoPie in memory

[avi-starkware]

Summary

• Add stwo_run_and_prove module that passes CairoPie directly to the prover library via SimpleBootloaderInput, offloading sync work to spawn_blocking.
• Add proving::error module with StwoRunAndProveError.
• Simplify prover::prove to create temp files only for outputs and call prove_pie_in_memory.
• Un-ignore the integration test (no external binary needed).

Stack: 3/4 — pure behavior PR for the in-memory proving path (no workflow/container noise).

Depends on: #12708

Test plan

• cargo test -p starknet_os_runner --features stwo_proving --release
• cargo test -p starknet_os_runner (default features still compile)

🤖 Generated with Claude Code

---

Note

Medium Risk
Touches the core proving execution path and changes how inputs are constructed and passed into the prover, which could affect correctness/performance and error propagation despite limited surface area.

Overview
Updates prover::prove to use a new in-memory proving path: it no longer writes the Cairo PIE and bootloader input to temp files, and instead calls prove_pie_in_memory while still emitting proof and program output to temporary files.

Adds proving::stwo_run_and_prove as a thin wrapper around stwo_run_and_prove_lib that builds SimpleBootloaderInput from a CairoPie and runs the synchronous prover via tokio::task::spawn_blocking, plus a dedicated StwoRunAndProveError type for join/prover failures. The previously ignored proving integration test is un-ignored since it no longer depends on an external stwo_run_and_prove binary.

^{Written by Cursor Bugbot for commit 73bc9ab. This will update automatically on new commits. Configure here.}

[reviewable-StarkWare]

This change is 

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• Started at 2026-02-18T20:55:05Z
• Started at 2026-02-18T21:16:41Z
• Started at 2026-02-18T21:16:41Z

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

[AvivYossef-starkware]

@AvivYossef-starkware reviewed 5 files and all commit messages, and made 4 comments.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on avi-starkware, noaov1, and Yoni-Starkware).

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crates/starknet_os_runner/src/proving/prover.rs line 44 at r2 (raw file):

/// Passes CairoPie directly to the prover library, avoiding disk I/O for the input.
/// The proof output is still written to a temporary file. The synchronous proving work
/// is offloaded to a blocking thread inside `prove_pie_in_memory`.

Suggestion:

/// Proves a Cairo PIE using the stwo prover lib.
/// The synchronous proving work
/// is offloaded to a blocking thread inside `prove_pie_in_memory`.

---

crates/starknet_os_runner/src/proving/prover_test.rs line 22 at r2 (raw file):

/// Run with: `cargo test -p starknet_os_runner -- --ignored test_prove_cairo_pie_10_transfers`
#[tokio::test]
#[ignore]

Can devs run it locally without OOM?

Code quote:

#[ignore]

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crates/starknet_os_runner/src/proving/stwo_run_and_prove.rs line 24 at r2 (raw file):

    let task_spec = TaskSpec { task: Rc::new(task), program_hash_function: HashFunc::Blake };
    SimpleBootloaderInput { fact_topologies_path: None, single_page: true, tasks: vec![task_spec] }
}

SimpleBootloaderInput::from(cairo_pie)

Code quote:

/// Creates a `SimpleBootloaderInput` from a `CairoPie` for in-memory proving.
///
/// This wraps the CairoPie in the appropriate task structures expected by the
/// simple bootloader, avoiding the need to serialize to disk.
fn create_bootloader_input_from_pie(cairo_pie: CairoPie) -> SimpleBootloaderInput {
    let task = Task::Pie(cairo_pie);
    let task_spec = TaskSpec { task: Rc::new(task), program_hash_function: HashFunc::Blake };
    SimpleBootloaderInput { fact_topologies_path: None, single_page: true, tasks: vec![task_spec] }
}

---

crates/starknet_os_runner/src/proving/stwo_run_and_prove.rs line 52 at r2 (raw file):

    })
    .await??)
}

consider deleting it

Code quote:

/// Runs the stwo prover on a CairoPie in-memory.
///
/// The synchronous proving work is offloaded to a blocking thread via
/// `tokio::task::spawn_blocking`.
///
/// # Arguments
///
/// * `bootloader_program_path` - Path to the compiled simple bootloader program.
/// * `cairo_pie` - The CairoPie to prove.
/// * `program_output_path` - Optional path for program output (proof facts).
/// * `prove_config` - Configuration for the prover.
pub(crate) async fn prove_pie_in_memory(
    bootloader_program_path: PathBuf,
    cairo_pie: CairoPie,
    program_output_path: Option<PathBuf>,
    prove_config: ProveConfig,
) -> Result<(), StwoRunAndProveError> {
    Ok(tokio::task::spawn_blocking(move || {
        prove_pie_in_memory_sync(
            bootloader_program_path,
            cairo_pie,
            program_output_path,
            prove_config,
        )
    })
    .await??)
}

[Yoni-Starkware]

@Yoni-Starkware made 1 comment.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on avi-starkware and noaov1).

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crates/starknet_os_runner/src/proving/prover.rs line 11 at r2 (raw file):

use cairo_air::utils::ProofFormat;
use cairo_vm::vm::runners::cairo_pie::CairoPie;
use proving_utils::proof_encoding::ProofBytes;

Are you planning to remove this crate at the end? its name is problematic (similar to stwo's repo) so easier is to merge the leftovers with the starknet_os_runner (and maybe rename this one to *_prover)

Code quote:

proving_utils