[DarkBiscuits]

A custom Mach3 post header containing G91.1 could generate G-code but then fail its automatic read-back with “G code is not an integer”, preventing CLI output.

Accept G91.1 as confirmation of incremental IJK centres in read_back, audit, and audit_five. Reject G90.1 with a specific unsupported-absolute-centres diagnostic. Endpoint positioning, built-in headers, and writer behavior are unchanged; absolute arc centres remain outside this change.

Regression coverage exercises custom-header/full-circle round-tripping, unchanged arc and helix geometry, declaration placement and equivalent numeric spelling, unsupported codes, and existing router probe support.

Validation on Linux (Rust 1.95):

• All four focused arc_centre_mode tests passed.
• Complete unmodified scripts/check.sh passed: formatting, workspace Clippy with warnings denied, workspace tests, wasm library checks, and license checks.
• The original synthetic ring-pocket CLI reproduction succeeded, including automatic read-back, and produced G-code containing G91.1 plus valid IR JSON.

AI disclosure: this patch, tests, review, and validation were developed with AI assistance using CAMpanion sources and synthetic inputs, following the repository's clean-room contributor rules. No physical controller testing was performed.

Fixes #144.

[mountainarcwelding]

Thanks for these, really appreciate the quick turnaround and the tests. I've kicked off CI and will review once it's green. One small ask: could you change "Fixes #144" to "Refs #144"? I keep issues open until a fix has been run on a real machine, so I'd rather they not auto-close on merge.