Portal saves the full machine state — env chain, compiled procedures,
continuations, frame stack — to a JSON file. Another interpreter
instance loads it and resumes execution from the exact instruction.
Demo: start a primality test on machine A, checkpoint mid-computation,
resume on machine B. 1000000007 prime check: machine B picks up from
i=30000 and finishes in 6% of the original time.
Implementation:
- PortalSerializer: graph-aware with identity tracking for shared env
references. Handles cycles (closures referencing their own env).
- portal-checkpoint!: triggers mid-execution save from within VM loop.
Hooks into TAIL_CALL (loop back-edge) for compiled code.
- --portal-resume CLI flag: load .portal file and resume continuation.
- portal-save / portal-resume Scheme builtins.
571 tests green (7 new portal tests: unit + integration + functional).
