Not only don't I have home switches, I don't have any automatic spindle control, so I'm quite used to starting it manually! In the past, I have used the "move back to machine (0,0,0)" technique at the end of a session to save having to tweak things at the start of the next - just need to hit "manual home" on the 3 axes and I'm ready to go. Hadn't thought about doing this if I have to pause a session, but will need to note machine/work offsets and current gcode line number. Point about missing out bits of header noted, but in practice I couldn't necessarily jump back to the line where I stop as I need to make sure that if, for example, it moves X only then I have to make sure that Y and Z are correct first, so going back slightly earlier in the file may make sense. Not a big deal to manually type any feedrate-type parameters first. Not sure what things like default for G64 are with LinuxCNC but I can look that up. LinuxCNC also lets you start from any line.
Thanks for comments, guys. Sometimes you need someone to point out what you knew but had forgotten... Now back to drawing the Mk2 while riding shotgun on this interminable cut. I was at least able to pick up accurate enough reregistration to carry on more or less from where I was when the PC failed.