Update expensive migration check

[sudo-shashank]

Summary of changes

Changes introduced in this pull request:

• Port fix(eth): serve eth_call at the epoch after an expensive migration filecoin-project/lotus#13644

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Bug Fixes

  • Fixed eth_call and eth_estimateGas no longer immediately rejected after expensive network-upgrade migrations; only the upgrade epoch is refused.
  • Expensive-fork rejections now return standardized error code with fork epoch information for improved diagnostics.

• Tests

  • Updated test environment configurations and expensive-fork error scenarios.

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Walkthrough

Error::ExpensiveFork is extended from a unit variant to a struct variant carrying epoch: ChainEpoch. ChainConfig gains expensive_fork_between returning the lowest matching epoch in a half-open range. A new JSON-RPC code -32002 is mapped from this error. eth_getCode, eth_getStorageAt, and apply_message are updated with epoch-aware guards and retry loops that rewind the execution-context tipset on expensive-fork, rather than refusing.

Changes

Expensive Fork Epoch Payload and ETH RPC Retry

Layer / File(s)	Summary
Error::ExpensiveFork epoch payload and ChainConfig::expensive_fork_between src/state_manager/errors.rs, src/networks/mod.rs	Error::ExpensiveFork becomes a struct variant with epoch: ChainEpoch. ChainConfig gains expensive_fork_between(parent, height) -> Option<ChainEpoch> returning the lowest expensive migration epoch in [parent, height), and has_expensive_fork_between delegates to it. Unit tests cover calibnet windows.
JSON-RPC -32002 error code and ServerError mapping src/rpc/error.rs	Adds EXPENSIVE_FORK_CODE = -32002 constant. Extends From<anyhow::Error> for ServerError to downcast ExpensiveFork { epoch } and return the new code with epoch as JSON error data.
call_raw expensive-fork detection refactor src/state_manager/message_simulation.rs	Replaces parent-tipset-load + has_expensive_fork_between with a fork_floor/fork_height range based on whether state_cid is provided, then queries chain_config.expensive_fork_between and returns Error::ExpensiveFork { epoch }.
ETH RPC apply_message guard, retry loops, and eth_estimateGas src/rpc/methods/eth.rs	apply_message guard switches to has_expensive_fork_between(ts.epoch(), ts.epoch()+1) returning ExpensiveFork { epoch: ts.epoch() }. eth_getCode and get_storage_at replace iteration attempts with retry loops keeping state_root fixed while rewinding ts to its parent on ExpensiveFork. eth_estimate_gas failure branch retries via apply_message to surface ExecutionReverted errors.
StateCall::run pattern match update src/rpc/methods/state.rs	Updates the error match arm to Error::ExpensiveFork { .. } for the new struct variant, preserving parent-tipset reload and retry behavior.
API compare test fixes, CHANGELOG, and Lotus image bump src/tool/subcommands/api_cmd/api_compare_tests.rs, CHANGELOG.md, scripts/tests/api_compare/.env	Test filter tightened to < heaviest_tipset.epoch() and EthCall target moved to expensive_fork_epoch + 1. CHANGELOG documents updated behavior. LOTUS_IMAGE bumped to v1.36.1-rc1-calibnet.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant eth_getCode/eth_getStorageAt
    participant call_raw
    participant ChainConfig

    Client->>eth_getCode/eth_getStorageAt: request at tipset ts
    eth_getCode/eth_getStorageAt->>call_raw: call_on_state(state_root, ts)
    call_raw->>ChainConfig: expensive_fork_between(fork_floor, fork_height)
    ChainConfig-->>call_raw: Some(epoch)
    call_raw-->>eth_getCode/eth_getStorageAt: Err(ExpensiveFork { epoch })
    eth_getCode/eth_getStorageAt->>eth_getCode/eth_getStorageAt: ts = ts.parents()
    eth_getCode/eth_getStorageAt->>call_raw: call_on_state(state_root, parent_ts)
    call_raw->>ChainConfig: expensive_fork_between(...)
    ChainConfig-->>call_raw: None
    call_raw-->>eth_getCode/eth_getStorageAt: Ok(result)
    eth_getCode/eth_getStorageAt-->>Client: result

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• ChainSafe/forest#7061: Directly modifies StateManager::call_raw and Error::ExpensiveFork handling in src/state_manager/message_simulation.rs, which is the core logic this PR extends.

Suggested reviewers

• akaladarshi
• LesnyRumcajs

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 46.67% 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 'Update expensive migration check' clearly and concisely summarizes the main objective of the pull request, which is to port changes that refactor expensive fork/migration checking logic across multiple modules.
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

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• Commit unit tests in branch shashank/update-expensive-migration-check

✨ Simplify code

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• Commit simplified code in branch shashank/update-expensive-migration-check

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