fix: key subject-path FromHexError by the meta hash verbatim

[thedavidmeister]

Closes #177

The defect

MetaboardSubgraphClient::get_metabytes_by_subject built the FromHexError key as encode(&meta.meta_hash.0). meta_hash is a Bytes(String) already holding a 0x… hex string, so encode hex-encoded its UTF-8 bytes: 0xabcd rendered as 307861626364, a value that matches nothing in the subgraph. The by-hash path already carries the hash string verbatim.

The fix

metahash: meta.meta_hash.0.clone() — the string as it came off the wire, consistent with the by-hash path and with the "Error decoding metahash {metahash}" message the variant renders. The issue flagged the key format as a maintainer call; this is the reading that makes the rendered key mean what the message says it means, and the only one that keeps the two paths consistent.

QA

• Discriminating tests: metaboard_client::tests::test_get_metabytes_by_subject_invalid_hex_meta — fails on base. The test predates this PR but deliberately pinned only the variant and non-emptiness of the key pending triage of get_metabytes_by_subject FromHexError identifies the meta by hex-of-ASCII of its hash string, not by the hash #177; it is tightened here to assert_eq!(metahash, "0xabcd"). Verified by reverting the one-line source change and re-running: test result: FAILED. 0 passed; 1 failed, with left: "307861626364", right: "0xabcd" — the issue's stated repro value exactly.
• Mutations applied: crates/metaboard/src/metaboard_client.rs:121 → metahash: encode(&meta.meta_hash.0) (the pre-fix source) → killed by test_get_metabytes_by_subject_invalid_hex_meta (left: "307861626364"). Same line → metahash: subject.0.clone() (key by the subject instead of the meta's own hash — the other plausible reading) → killed by the same test (left: "0x7c", the mock's subject, vs the mock's metaHash 0xabcd). Both mutations were compiled and run.
• Oracle: the issue's intent oracle, independent of the implementation — the variant's own #[error("Error decoding metahash {metahash}: {source}")] declares the field to be a metahash, and the sibling by-hash path (metahash: metahash.clone(), a 0x… string) fixes the format. The expected value 0xabcd is the metaHash the mocked subgraph response returns, read off the test fixture.
• Category check: the issue asks one thing — the subject-path FromHexError key must identify the meta by its hash rather than by hex-of-ASCII of that hash string; covered. Checked every encode( call in the crate: no other site builds a field from an already-hex string (get_metabytes_by_hash and get_metaboard_addresses both carry their string verbatim).

Verification

cargo test -p rain-metaboard-subgraph --lib metaboard_client — 12 passed, 0 failed. cargo fmt --all --check and cargo clippy -p rain-metaboard-subgraph --all-targets -- -D warnings clean.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Corrected error reporting for invalid metadata hashes.
  • Error details now display the original hash value without redundant encoding, making invalid-hash issues clearer and easier to diagnose.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: 5bbe0cfe-7402-4d53-946d-81886839b5c9

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Reviewing files that changed from the base of the PR and between 45ca96c and 605a91e.

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• crates/metaboard/src/metaboard_client.rs

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Walkthrough

get_metabytes_by_subject now reports the offending meta hash verbatim in FromHexError. The related test documents this contract and asserts the exact key "0xabcd".

Changes

Meta hash error reporting

Layer / File(s)	Summary
Use and validate the verbatim meta hash crates/metaboard/src/metaboard_client.rs	The subject lookup stops double-encoding the meta hash. The test documentation and assertion verify the exact metahash value "0xabcd".

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 605a9

The change makes subject-based decoding errors identify the returned metadata hash verbatim, with targeted tests and standard checks passing; no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: using the meta hash verbatim for the subject-path FromHexError key.
Linked Issues check	✅ Passed	The changes satisfy issue #177 by replacing double-encoding with the original meta hash string and by asserting the exact expected key in the test.
Out of Scope Changes check	✅ Passed	The implementation, test update, and documentation change are directly related to correcting the FromHexError key. No unrelated changes are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 1 files.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
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📝 Generate docstrings

• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-08-25-issue-177

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