Nice!

@rodw

Agreed that the planner should be true to the physics, but the physics here has two valid outcomes depending on the machine. A small bounded jerk spike on a 1ms grid at a sharp corner is absorbed transparently by any drive with internal interpolation, the part comes out correct, no stop needed. On a drive without internal interpolation, the spike is real and a stop is the right answer. Both are physically correct responses to the same situation on different hardware.

The point is not to hide the problem but to give the integrator the right tool to handle it. A blind stop at every corner where the jerk limit cannot be met on the 1ms grid would significantly hurt cycle time on complex CAM toolpaths for no benefit on machines where the drive handles it anyway.

The proposal on the table is a new modal G64.1 P Q
jerk-aware continuous path mode that behaves like G64 P Q but adds automatic full stop fallback when the jerk-constrained cornering velocity rounds to zero. Off by default to preserve existing behavior, opt-in for integrators who need provably clean command streams or are running drives without internal interpolation. That seems like the right balance between being true to the physics and being useful across the wide range of hardware LinuxCNC runs on.

@endian
Exactly right, the cycle time is a fundamental constraint that belongs in the tolerance budget, not something to fight against. G-code level control of spike tolerance makes a lot of sense and aligns well with what I have been discussing as a TP option.

@rodw
Fair point in an ideal world, but LinuxCNC has to interface with a very wide range of CAM outputs, many of which the end user has no control over. We should strive for maximum compatibility. Yes, some G-code will be genuinely nonsense and will need fixing at the source, but for cases where the geometry is valid and the only issue is a parameter mismatch between the toolpath and the machine limits, an INI or G-code option that lets the integrator choose the behavior is the right balance rather than rejecting the job outright.