feat(zkvm): share witness/fixed Jagged inner opening

[hero78119]

Problem

Ceno opens witness and fixed Jagged commitments in the same proof, but the previous integration still paid for separate inner Basefold openings. That duplicates inner query/opening proof bytes even though witness/fixed can share the same inner Basefold query set.

Design Rationale

Keep the outer Jagged protocol literally separate while sharing only the inner Basefold opening:

• witness and fixed keep separate Jagged commitments and separate Merkle roots
• witness and fixed keep separate Jagged sumcheck/assist rounds
• each round keeps its own q' shape and reshape height from its existing commitment lifecycle
• Ceno collects each Jagged round's inner opening claims and calls one Basefold batch_open_with_trace_materializer
• the resulting JaggedProof contains all Jagged rounds plus one required shared inner_proof

This is intentionally surgical: it does not refactor witness lifecycle, q' ownership, q' residency, or fixed/witness commit paths. The only integration change is moving inner Basefold opening from per-Jagged-round execution to one batched inner opening after all Jagged reductions.

Soundness/correctness rationale: prover and verifier transcript order is aligned with gkr-backend: absorb all Jagged round reductions first, then absorb/verify one inner Basefold opening over all inner claims. Commitments remain independent, so sharing the inner proof does not merge witness/fixed roots.

Change Highlights

• ceno_zkvm/src/scheme/gpu/mod.rs
  • GPU Jagged opening now collects (round_proof, rho_row, col_evals) for each Jagged round.
  • Builds per-round inner opening claims without changing q' lifecycle.
  • Calls one shared GPU Basefold batch_open_with_trace_materializer for witness/fixed inner claims.
• ceno_zkvm/src/scheme.rs
  • Extends existing proof-size display to include PCS-specific nested breakdowns.
• Cargo.toml
  • Pins gkr-backend and ceno-gpu dependencies to feat/jagged_single_commit.

Benchmark / Performance Impact

Operation

Operation	master (s)	this PR (s)	Improve (master -> this PR)
reth-block	11.143	11.087	+0.056s
app.prove	10.579	10.559	+0.020s
create_proof_of_shard	6.315	6.509	-0.194s
commit_traces	1.354	1.535	-0.181s
pcs_opening	1.492	1.483	+0.009s
shard-0 proof size	6.15 MiB	5.48 MiB	+0.67 MiB smaller (-10.96%)

Layer

Layer	master (s)	this PR (s)	Improve (master -> this PR)
Basefold witness commit/query	0.423 / 0.270	0.427 / 0.269	approximately flat
Basefold fixed commit/query	0.0147 / 0.00325	folded into shared opening	removes separate inner proof
Jagged outer rounds	separate witness/fixed	separate witness/fixed	unchanged by design

Proof-size breakdown, shard 0

Sizes are MiB, computed as bytes / 2^20. Percent is relative to the after proof file (5.48 MiB).

Component	Size	% of Proof
Proof file app_proof.bitcode	5.48 MiB	100.00%
mpcs_opening.total	1.09 MiB	19.95%
mpcs_opening.rounds	0.008 MiB	0.14%
round[0] witness Jagged round	0.005 MiB	0.09%
round[1] fixed Jagged round	0.003 MiB	0.05%
shared inner_proof	1.09 MiB	19.81%
inner_proof.query_opening_proof	1.08 MiB	19.78%
inner_proof.commits	0.001 MiB	0.01%
inner_proof.sumcheck_proof	0.001 MiB	0.02%
inner_proof.final_message	0.0003 MiB	0.01%

Raw proof-size data:

Metric	Before	After	Delta
Shard 0 proof file	6,453,943 B	5,746,603 B	-707,340 B (-10.96%)
Single proof object	n/a	5,746,602 B	n/a
mpcs_opening.total	n/a	1,146,525 B	n/a
shared inner_proof	n/a	1,138,405 B	n/a

Testing

cargo fmt -p ceno_zkvm
cargo check -p ceno_zkvm --features gpu

Additional dependency checks:

# gkr-backend
cargo fmt -p mpcs
cargo check -p mpcs
cargo check -p mpcs --all-targets

# ceno-gpu
cargo fmt -p cuda_hal
cargo check -p cuda_hal --features bb31

E2E validation:

• ../ceno-reth-benchmark, block 23587691, shard 0, GPU, prove-app, verifier passed.

Risks and Rollout

Risk is transcript/order mismatch because inner Basefold proof generation moved out of each Jagged round and into one shared call after all Jagged reductions. The verifier mirrors this order in gkr-backend, and shard-0 e2e verification passed.

Performance risk is low: proof size improves materially while pcs_opening is flat on the measured shard. commit_traces varied upward in this run, but this PR does not change commit lifecycle or q' materialization.

Rollback is localized: restore the previous per-Jagged-round inner opening path and the old dependency pins.

Follow-ups (optional)

None required for this PR. Broader cleanup can later remove temporary local benchmark patching once dependency branches are merged.

Copilot Reviewer Directive (keep this section)

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