onebrc/lane-j: typed GridlakeCarrierError (addresses #641 review)

[AdaWorldAPI]

What

Addresses the CodeRabbit review on #641 (merged): GridBatch::as_gridlake_columns returned Result<GridlakeColumns, ()> with a #[allow(clippy::result_unit_err)], which lost the diagnostic context of which grid failed alignment.

• Replaces the unit error with GridlakeCarrierError::UnalignedGrid { grid: usize } — surfaces the offending grid size, drops the #[allow], and impls Display + std::error::Error.
• The unaligned-grid test now asserts the variant (grid = 72).

Why a plain enum, not snafu

The reviewer suggested a snafu-derived error. onebrc-probe is a workspace-excluded standalone probe whose lanes A/C are dependency-free by design (documented in its Cargo.toml) — a snafu type would drag a new dependency into a crate that deliberately carries none. A plain enum gives the same diagnostic context (grid size, Display, Error) without that cost, which fits this crate better than the repo-wide snafu guideline the auto-review applied.

The other #641 comment

CodeRabbit also flagged the STATUS_BOARD.md change as breaking append-only ordering. That's a false positive: the board's sections are ordered newest-first (the 2026-07-04 section on top, then 07-02, then older), and this prepended a new section — it did not reorder or rewrite any prior entry, so provenance is preserved. No change made there.

Verification

cargo test --manifest-path crates/onebrc-probe/Cargo.toml --features lane-j — 2/2 gridlake tests green (LE roundtrip + unaligned-grid variant assertion). lane_j.rs fmt + clippy clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MLBnPuScZy6w9di2QEjsXM

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Generated by Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between d057605 and 1f36637.

📒 Files selected for processing (1)

• crates/onebrc-probe/src/lane_j.rs

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