refactor(engine-api): remove engine_appendBatchSignature and BatchSignature

[panos-xyz]

Summary

Remove the engine_appendBatchSignature RPC stub and the BatchSignature type. The consensus layer (tendermint / morphnode) no longer calls this method after batch generation is moved out of the consensus path to the tx-submitter.

Cross-repo coordination

This PR is the morph-reth counterpart of:

• Remove sequencer batch write paths and unused NewL2Block batch hash go-ethereum#319 — remove sequencer batch write paths + drop unused NewL2Block batch hash
• feat: remove sequencer batch generation from consensus layer tendermint#35 — remove sequencer batch generation from consensus layer
• refactor: remove sequencer batch generation and BLS signing morph#939 — remove sequencer batch generation and BLS signing

Scope

morph-reth only ever carried a no-op stub for engine_appendBatchSignature (added in #93 to prevent morphnode's retry loop from hanging the tendermint goroutine). morph-reth never implemented the geth-side batch write paths (CommitBatch, RollupBatch DB accessors, batch.Handler lifecycle), so there is no equivalent cleanup needed here — only the stub goes away.

batch_hash was already removed from MorphHeader in #31, and newL2Block already has no batchHash parameter in reth.

Changes

• Delete append_batch_signature default method from MorphL2EngineApi trait (crates/engine-api/src/api.rs)
• Delete append_batch_signature method from MorphL2EngineRpc trait + MorphL2EngineRpcHandler impl (crates/engine-api/src/rpc.rs)
• Delete BatchSignature struct (crates/payload/types/src/params.rs)
• Drop BatchSignature re-export (crates/payload/types/src/lib.rs)
• Drop engine_appendBatchSignature row from README Engine API table

Net diff: 5 files, +4 / -68.

Deployment ordering

This PR should land together with (or after) the coordinated PRs in go-ethereum / tendermint / morph. Running a newer morph-reth without the engine_appendBatchSignature endpoint against an older morphnode that still calls it would trigger the same "Method not found" retry storm that #93 originally fixed.

Test plan

• cargo check --workspace
• cargo clippy --all --all-targets -- -D warnings
• cargo nextest run --workspace
• Smoke test against a morphnode built from refactor: remove sequencer batch generation and BLS signing morph#939 (no retry storm, blocks continue to sync)

Summary by CodeRabbit

• Chores
  • Removed the appendBatchSignature API method from the Engine API along with its type definitions and JSON-RPC endpoint.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 61926973-d2bd-4af6-a70d-8d3c0b5a84c5

📥 Commits

Reviewing files that changed from the base of the PR and between cc7372a and ec7c735.

📒 Files selected for processing (2)

• crates/engine-api/src/api.rs
• crates/engine-api/src/rpc.rs

📝 Walkthrough

Walkthrough

This PR removes the batch signature feature from the Engine API, eliminating the append_batch_signature method from the core trait and RPC layer, the corresponding BatchSignature type definition, and all related documentation.

Changes

Cohort / File(s)	Summary
Documentation README.md	Removes the documented engine_appendBatchSignature API endpoint description.
API Trait and RPC Layer crates/engine-api/src/api.rs, crates/engine-api/src/rpc.rs	Removes the append_batch_signature async method from MorphL2EngineApi trait and the corresponding appendBatchSignature JSON-RPC method from MorphL2EngineRpc trait and its handler implementation.
Type Definitions crates/payload/types/src/lib.rs, crates/payload/types/src/params.rs	Removes BatchSignature re-export from public API and deletes the complete BatchSignature struct definition with all its fields (signer, signer_pub_key, signature).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• feat: add morph engine api #12 — Defines/modifies the same MorphL2EngineApi trait and RPC surface affected by these removals.
• fix(engine-api): add engine_appendBatchSignature RPC for sync nodes #93 — Adds the append_batch_signature method and BatchSignature type in the same locations where this PR removes them.

Suggested reviewers

• chengwenxi
• anylots

Poem

🐰 A signature once passed through the chain,
But batch by batch, it caused us pain,
Now cleanly swept, the API shines bright,
No more appendBatchSignature in sight! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: removing the engine_appendBatchSignature RPC method and BatchSignature type from the codebase, which aligns with all the modifications across multiple files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/remove-batch-signature

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