amiagent 0.5.2 — give commands a real stack

Upgrade if you use amimcp to launch anything with a GUI. This fixes a second crash that could take the whole machine down.

A command inherits the stack of the process the agent creates for it, and that was 16 KB. Fine for AmigaDOS commands, nowhere near enough for a GUI program. A 68k program that overruns its stack does not fail politely — it takes the machine with it.

ScummVM launched through the agent crash-rebooted an A4000 again and again, while the same binary started fine from Workbench — because a Workbench icon specifies its own stack and the agent did not. ScummVM --version always worked, which is precisely the tell: it exits before the call depth grows.

NP_StackSize is now 256 KB, passed both to the job process and through SystemTags to the command itself. On a machine with hundreds of megabytes free, being stingy there bought nothing and cost an evening.

Together with 0.5.1

0.5.1 fixed a use-after-free on a closing Screen. Between them these were responsible for every machine-down crash seen while driving a GUI program remotely — the program being driven was innocent throughout.