feat(core): move DeepestErrorFinder into dedicated deepest_error.rs

[JuliobaCR]

Summary

Closes #393.

DeepestErrorFinder was previously implemented as part of #378 inside chain_analyzer.rs. This PR moves it into its own dedicated module, crates/core/src/decode/deepest_error.rs, matching the file location specified in #393.

• DeepestError / DeepestErrorFinder / find_deepest_error extracted into crates/core/src/decode/deepest_error.rs.
• Shared call-stack bookkeeping and failure-detection helpers (is_failure, topic_to_string, hash_to_strkey, StackFrame) made pub(crate) in chain_analyzer.rs so the two analyzers reuse identical logic instead of duplicating it.
• Re-exported from decode::mod (DeepestError, DeepestErrorFinder, find_deepest_error).
• Fixed an off-by-one bug in the reported call depth: it was computed from the post-push stack length instead of the depth of the frame that was actually active when the failure fired. This under-reported the depth by one on every failure nested 2+ levels deep (e.g. a 3-call chain reported depth 3 instead of 2).
• Added test coverage for 4-level nested failures and recursive re-entry, in addition to the existing cases carried over from DeepestErrorFinder: pinpoint root via event depth #378.

Test plan

• cargo test -p grat-core --lib -- decode:: — 212 passed, 0 failed (includes 20 deepest_error tests, all chain_analyzer/walker tests unaffected).
• Verified the depth fix by hand-tracing the call-stack algorithm against the multi-level nested-failure test cases.

Note: main currently fails to build (cargo check -p grat-core) due to ~15 pre-existing, unrelated errors in multi_op_decoder.rs and report.rs (likely from an incomplete merge of #390). Those are out of scope here; to validate this change I temporarily patched around them in a disposable local clone only, not in this branch.

[coderabbitai]

Important

• 🔍 Trigger review

This repository does not receive automatic reviews because it has fewer than 10 stars.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: acc76df2-6f77-4cf4-a652-5054b9c896fb

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[JuliobaCR]

The failing Rust Checks / Check formatting step is not caused by this PR. cargo fmt --check runs repo-wide, and it stops on pre-existing, unrelated formatting drift in files this PR never touches, e.g. argument_decoder.rs, return_decoder.rs, spec/decoder.rs, spec/tests/wasm_tests.rs. This diff itself (chain_analyzer.rs, deepest_error.rs, decode/mod.rs) is rustfmt-clean.

The job never even reaches the compile/test steps because it fails at formatting first, but for reference, main also currently fails cargo check -p grat-core on its own (~15 unrelated errors in multi_op_decoder.rs and report.rs, likely from an incomplete merge of #390), as noted in the PR description. I verified this change compiles and passes (cargo test -p grat-core --lib -- decode:: → 212 passed, 0 failed) by patching around those pre-existing issues in a disposable local clone only , none of that is part of this diff.

Happy to rebase once main is green again, or to open a separate issue for the formatting/build breakage if that's useful.

[codeZe-us]

@JuliobaCR thanks, yes i will resolve the formatting issues on my end, i have reviewed your PR, it is okay. Thanks.

[codeZe-us]

@JuliobaCR fix conflicts in your pr, main branch issues have been resolved

[codeZe-us]

@JuliobaCR i am expecting your changes

[JuliobaCR]

@codeZe-us Conflicts resolved — rebased onto the updated main and force-pushed.

• Rebased fix/393-deepest-error-dedicated-file onto main (now that the pre-existing build issues you mentioned are fixed).
• Resolved the two conflicts in chain_analyzer.rs / decode/mod.rs: main still had DeepestErrorFinder embedded in chain_analyzer.rs, while this branch had already moved it out to deepest_error.rs. Kept the moved version (it already carries its own 17 tests) and dropped the now-duplicated code/tests from chain_analyzer.rs.
• Fixed a couple of trivial clippy nits (map().unwrap_or(...) → map_or, single-match-else → if let) in the moved code while I was in there.

Verified locally (matching the CI steps):

• cargo fmt --all -- --check — clean
• cargo build --workspace --all-targets --all-features — clean
• cargo test --workspace --all-targets --all-features — 340 passed, 0 failed

PR now shows as mergeable/clean against main. Let me know if anything else is needed.

[codeZe-us]

@JuliobaCR Thanks, PR reviewed and merged