chore(storage): Add error handling on Store::get_forkchoice_store

[Aliemeka]

🗒️ Description / Motivation

Replace the assert_eq! in Store::get_forkchoice_store with a typed Result so callers see a descriptive error instead of a panic. The previous message ("block header doesn't match state's latest_block_header") gave no insight into which field actually differed, which made misconfigured anchor state/block pairs hard to diagnose. PR closes #360.

What Changed

• crates/storage/Cargo.toml — add thiserror dependency.
• crates/storage/src/store.rs — introduce pub enum GetForkchoiceStoreError with a HeaderMismatch { state_header, block_header } variant; change Store::get_forkchoice_store to return Result<Self, GetForkchoiceStoreError>; replace the assertion with an explicit comparison that returns Err; update the doc comment (# Panics → # Errors).

Correctness / Behavior Guarantees

• The validation rule is unchanged: anchor block header must equal the state's latest_block_header after zeroing state_root. Mismatches that previously aborted via assert_eq! now return Err(HeaderMismatch { … }), surfacing both full headers (boxed to keep the variant small) for diff-friendly debugging.
• Store::from_anchor_state is untouched. Internal panics in init_store (state_root mismatch and storage backend operations) are intentionally left as-is — they represent infrastructure invariants shared between both constructors and are out of scope for this change.

Tests Added / Run

• No new tests; the type change is enforced by the compiler and existing fork-choice / signature spec suites continue to exercise the success path.
• Ran make fmt, make lint, cargo test --workspace --release (unit tests pass; spec tests require make leanSpec/fixtures for fixture generation)
• Also ran make test

Related Issues / PRs

• Closes Add error handling on Store::get_forkchoice_store #360

✅ Verification Checklist

• Ran make fmt — clean
• Ran make lint (clippy with -D warnings) — clean
• Ran cargo test --workspace --release — all passing

[greptile-apps]

Greptile Summary

This PR converts Store::get_forkchoice_store from a panicking function into one that returns Result<Self, GetForkchoiceStoreError>, surfacing a descriptive HeaderMismatch error (with both headers boxed) instead of an opaque assert_eq! abort.

• crates/storage/src/store.rs: Introduces GetForkchoiceStoreError via thiserror, replaces assert_eq! with an explicit if returning Err(HeaderMismatch { … }), and updates the doc comment from # Panics to # Errors. The validation logic (zero state_root before comparison) is unchanged.
• crates/storage/src/lib.rs: Re-exports GetForkchoiceStoreError so downstream crates can pattern-match the variant.
• crates/blockchain/…: All three call sites (unit test, forkchoice spec tests, signature spec tests) updated to .expect("anchor state and block must match"), preserving the panic behavior in test/internal contexts where a mismatch is always a programmer error.

Confidence Score: 5/5

Safe to merge — the change is a straightforward replacement of a single assert_eq! with a typed Result return; no validation logic is altered.

The diff is narrow and mechanical: one assertion becomes an if-guard returning Err, one new error enum is introduced with thiserror, and every call site is updated. The zeroing of state_root before comparison — the only subtlety in the original code — is preserved exactly. The remaining assert! calls inside init_store are explicitly out of scope and untouched.

No files require special attention.

Important Files Changed

Filename	Overview
crates/storage/src/store.rs	Introduces GetForkchoiceStoreError::HeaderMismatch and converts get_forkchoice_store from a panicking function to Result<Self, GetForkchoiceStoreError>; logic is unchanged.
crates/storage/src/lib.rs	Re-exports the new GetForkchoiceStoreError type so downstream crates can match on the error variant.
crates/storage/Cargo.toml	Adds thiserror as a workspace dependency to support the new error derive macro.
crates/blockchain/src/store.rs	Updates the internal unit test call site to use .expect(...) on the now-fallible get_forkchoice_store.
crates/blockchain/tests/forkchoice_spectests.rs	Updates spec-test harness call site to .expect(...) on the fallible constructor.
crates/blockchain/tests/signature_spectests.rs	Updates signature spec-test harness call site to .expect(...) on the fallible constructor.

Sequence Diagram

sequenceDiagram
    participant Caller
    participant get_forkchoice_store
    participant init_store

    Caller->>get_forkchoice_store: (backend, anchor_state, anchor_block)
    get_forkchoice_store->>get_forkchoice_store: zero state_root on both headers
    alt headers match
        get_forkchoice_store->>init_store: (backend, anchor_state, Some(anchor_block.body))
        init_store-->>get_forkchoice_store: Store
        get_forkchoice_store-->>Caller: Ok(Store)
    else headers differ
        get_forkchoice_store-->>Caller: "Err(HeaderMismatch { state_header, block_header })"
    end

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_{Reviews (1): Last reviewed commit: "chore(storage): Add error handling on `S..." | Re-trigger Greptile}

[pablodeymo]

Hi @Aliemeka. Thanks for your contribution.

You must sign your commits. You can check that in here:
https://github.com/lambdaclass/ethlambda/blob/main/CONTRIBUTING.md#commit-signature-verification

[Aliemeka]

So sorry for force pushing. I just got confused about signing my commit