feat: add eth_baseFee rpc method

[wjmelements]

Adds the nonstandard eth_baseFee eth jsonrpc method.
This method returns the calculated base fee of the next epoch.
See filecoin-project/lotus#13615

Changes

• add eth_baseFee
• regenerate snapshots

Summary by CodeRabbit

• New Features
  • Added eth_baseFee JSON-RPC method (also accessible as Filecoin.EthBaseFee) for Ethereum compatibility, allowing applications to query the network's current base fee.
  • Method is now included in the RPC method registry/OpenRPC spec so it’s discoverable via the API.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 080ecc52-cc5a-4ca6-8639-845ca2823dcb

📥 Commits

Reviewing files that changed from the base of the PR and between d7f773c and bbd1e5f.

📒 Files selected for processing (1)

• src/rpc/methods/eth.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/rpc/methods/eth.rs

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Walkthrough

This PR introduces a new Ethereum-compatible JSON-RPC method eth_baseFee (Filecoin.EthBaseFee) that computes and returns the base fee for the heaviest tipset. The implementation adds required imports, implements the handler logic using chain configuration height epochs, and registers the method in the RPC macro system.

Changes

Ethereum Base Fee RPC Method

Layer / File(s)	Summary
Imports & Dependencies src/rpc/methods/eth.rs	Added imports for compute_base_fee and ResolveNullTipset from crate::chain, and Height from crate::networks to support base fee calculation.
RPC Method Handler src/rpc/methods/eth.rs	Implemented EthBaseFee as a new RpcMethod<0> that derives Smoke and FireHorse epochs from ctx.chain_config().height_infos, computes base fee for the heaviest tipset via compute_base_fee, and returns the result as EthBigInt.
RPC Registration src/rpc/mod.rs	Registered the new EthBaseFee method in the for_each_rpc_method! macro's eth vertical registration list.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• ChainSafe/forest#6702: Updates to compute_base_fee signature and call sites that directly relate to the base fee computation introduced in this RPC method.

Suggested labels

RPC

Suggested reviewers

• LesnyRumcajs
• akaladarshi

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 accurately describes the main change: adding the eth_baseFee RPC method. It is specific, concise, and directly reflects the primary objective of the pull request.
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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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/rpc/methods/eth.rs`:
- Line 835: The call to compute_base_fee(...) can fail without contextual
information; wrap the call with .context(...) to add an explanatory message for
RPC diagnostics so errors include that compute_base_fee failed and the relevant
inputs (e.g., timestamp ts and heights smoke_height/firehorse_height) — locate
the call to compute_base_fee in eth.rs and change the invocation so the returned
Result is propagated with .context("compute_base_fee failed for ts/
smoke_height/ firehorse_height") (or similar) to satisfy the anyhow::Result
guideline.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 22c12b5e-0961-4079-9ad9-415b69b9ab92

📥 Commits

Reviewing files that changed from the base of the PR and between e2becd7 and d7f773c.

⛔ Files ignored due to path filters (3)

• src/rpc/snapshots/forest__rpc__tests__rpc__v0.snap is excluded by !**/*.snap
• src/rpc/snapshots/forest__rpc__tests__rpc__v1.snap is excluded by !**/*.snap
• src/rpc/snapshots/forest__rpc__tests__rpc__v2.snap is excluded by !**/*.snap

📒 Files selected for processing (2)

• src/rpc/methods/eth.rs
• src/rpc/mod.rs

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
2040	1	2039	0

View the top 1 failed test(s) by shortest run time

forest-filecoin::tool::subcommands::api_cmd::test_snapshot::tests::rpc_regression_tests_print_uncovered

Stack Traces | 0.019s run time

thread 'tool::subcommands::api_cmd::test_snapshot::tests::rpc_regression_tests_print_uncovered' (62234) panicked at .../subcommands/api_cmd/test_snapshot.rs:284:9:
either ignore or upload test snapshots for uncovered RPC methods
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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