feat(sumcheck): enable frontload dependency set

[hero78119]

Problem

Enable Ceno to consume the frontload sumcheck work from gkr-backend and ceno-gpu.

Design Rationale

This PR only updates dependency pins. The implementation lives in:

Area	Summary
gkr_iop / gkr-backend	Makes frontload/prefix sumcheck the default CPU path and keeps forced suffix available for comparison.
ceno-gpu	Adds frontload support to GPU sumcheck v2 kernels, removes legacy v1 flat-buffer kernels, and keeps PCS/basefold on suffix.

Change Highlights

• Update gkr-backend branch lock from the older frontload commit to the latest frontload dependency set.
• Keep all Ceno gkr-backend crates on one consistent revision to avoid duplicate sumcheck / transcript types.

Benchmark / Performance Impact

Benchmark: Reth GPU E2E, block 23817600, CENO_GPU_ENABLE_WITGEN=0.
Positive percentage means faster.

Metric	Baseline	This PR	Change
E2E total	75.400s	75.600s	-0.3%
app_prove	60.400s	61.000s	-1.0%
build_tower_witness_gpu	4.613s	3.491s	+24.3%
prove_main_constraints	24.364s	22.622s	+7.1%
pcs_opening	15.441s	15.246s	+1.3%
prove_tower_relation_gpu	172.341s	176.090s	-2.2%

GPU Span	Baseline	This PR	Change
Tower prove_generic_sumcheck_gpu	161.604s	168.859s	-4.5%
Main prove_generic_sumcheck_gpu	22.443s	21.244s	+5.3%
PCS batch_commit_phase	6.566s	6.453s	+1.7%
PCS batch_query_phase	4.615s	4.617s	-0.0%

Raw results:

• Baseline: https://github.com/scroll-tech/ceno-reth-benchmark/actions/runs/25241194699
• This PR: https://github.com/scroll-tech/ceno-reth-benchmark/actions/runs/25419833788

Testing

cargo install --git https://github.com/scroll-tech/ceno --branch feat/frontload --features jemalloc --features nightly-features --locked --force cargo-ceno
CENO_GPU_ENABLE_WITGEN=0 cargo run --features "jemalloc,gpu" --release --bin ceno-reth-benchmark-bin -- --mode prove-app --block-number 23817600

Risks and Rollout

Main risk is cross-repo dependency skew between ceno, gkr-backend, and ceno-gpu. Rollback is to revert the dependency update.

Follow-ups (optional)

Investigate tower GPU sumcheck regression while keeping PCS/basefold on suffix.

Copilot Reviewer Directive (keep this section)

When Copilot reviews this PR, apply .github/copilot-instructions.md strictly.

[hero78119]

@copilot update gkr-backend dependency to tag = "v1.0.0-alpha.26"

[Copilot]

Pull request overview

Updates Ceno’s gkr-backend dependency set to consume the latest “frontload/prefix” sumcheck work (CPU + GPU paths) while keeping all gkr-backend crates on a consistent revision to avoid duplicate types.

Findings (by severity):

• Major (Cargo.toml:30-34): gkr-backend crates are now referenced via a moving branch instead of an immutable tag/rev, which reduces reproducibility/supply-chain safety for any build that doesn’t rely on this repo’s Cargo.lock (and makes accidental upgrades easier via cargo update). A concrete mitigation is to pin with rev = "<commit>" (or use a new immutable tag) for the whole gkr-backend set.

Open questions / assumptions:

• Is the intent to track feat/frontload continuously, or to consume exactly commit f8847d88...? If the latter, switching to rev would better match the “dependency pin” goal stated in the PR description.

Changes:

• Move gkr-backend workspace dependencies from v1.0.0-alpha.25 to the feat/frontload line.
• Update Cargo.lock to the corresponding gkr-backend commit (f8847d88...) consistently across all affected crates.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Cargo.toml	Switch gkr-backend dependency references to feat/frontload.
Cargo.lock	Update locked gkr-backend sources to the new commit for the frontload set.

[Copilot]

@copilot update gkr-backend dependency to tag = "v1.0.0-alpha.26"

Updated all gkr-backend workspace deps to tag = "v1.0.0-alpha.26" and aligned Cargo.lock to the same tag commit in b19ea95.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/scroll-tech/gkr-backend/commits/feat/frontload
  • Triggering command: /home/REDACTED/.rustup/toolchains/nightly-2025-11-20-x86_64-REDACTED-linux-gnu/bin/cargo /home/REDACTED/.rustup/toolchains/nightly-2025-11-20-x86_64-REDACTED-linux-gnu/bin/cargo update -p sumcheck ewor�� lockfree_object_pool --edition=2021 /usr/bin/ld ibs -o tui_ui_sub tui_ui_sub.o libmpc-tests.la ../src/libmpc.la -lmpfr -lgmp -lm -lm (http block)
  • Triggering command: REDACTED, pid is -1 (http block)

If you need me to access, download, or install something from one of these locations, you can either:

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