Implement save/restore game state

[Copilot]

Game state could not be persisted between sessions. The fix moves dynamic state into mem so a mem dump captures everything, then adds SAVE/RESTORE primitives that serialize and deserialize that state.

Changes

zilscript/bootstrap.lua

• _ZGLOBALS = {} — global registry for ZIL game variable names, populated at runtime via SETG; consumed by SAVE/RESTORE
• SETG(name, val) / GETG(name) — new runtime functions; SETG sets the global in _G, registers its name in _ZGLOBALS, and returns the value; GETG reads from _G
• Object FLAGS → mem — OBJECT() allocates 8 bytes in mem per object (o._flags_addr) for the FLAGS bitmask; FSET/FCLEAR sync changes via write_flags_to_mem() so FLAGS are included in any mem dump
• SAVE(filename) — writes: magic header + mem bytes (object properties, locations, FLAGS) + ZIL global values from _ZGLOBALS; mem is written in 4 KiB chunks to stay within Lua's table.unpack limits
• RESTORE(filename) — reads the save file, restores mem, re-syncs all o.FLAGS caches from mem, then restores ZIL globals

zilscript/base.lua

• Minimal stub definitions of SETG/GETG (without _ZGLOBALS tracking) so ZIL modules loaded via the bare loader without bootstrap continue to work

zilscript/compiler/forms.lua

• GLOBAL form now emits SETG(%q, val) — global tracking happens automatically at runtime via the SETG function; no separate _ZGLOBALS registration line needed
• SETG form now emits SETG(%q, val) — consistent with GLOBAL, tracks globals at runtime
• CONSTANT is a separate handler and intentionally does not use SETG (immutable at runtime)

zil/test-save.zil

• New test: sets object location, object flags (ONBIT), and numeric/boolean globals → saves → mutates all state → restores → asserts exact match

Save file format

"ZILSAVE\1"      8 bytes  magic + version
mem_size         4 bytes  LE uint32
mem_data         N bytes  raw mem bytes (includes object FLAGS at o._flags_addr)
global_count     2 bytes  LE uint16
  name_len       1 byte
  name           N bytes
  type           1 byte   1=number, 2=boolean
  value          8 or 1 bytes

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[corepunch]

@copilot Do you need _ZGLOBALS? there are SETG and GETG hence you can make these
<GLOBAL TROLL-FLAG <>>
just 2 byte values (to be safe) in mem and set TROLL-FLAG to it's address
And we assume next time game is loaded, these addresses will match, right?

[corepunch]

@copilot You'll need to modify compiler to emit SETG and GETG and add these functions to bootstrap

[Copilot]

@copilot Do you need _ZGLOBALS? there are SETG and GETG hence you can make these
<GLOBAL TROLL-FLAG <>>
just 2 byte values (to be safe) in mem and set TROLL-FLAG to it's address
...

Good point. Replaced the compile-time _ZGLOBALS[%q] = true emission with proper SETG(name, val) and GETG(name) runtime functions. SETG now populates _ZGLOBALS automatically whenever a global is set, so the compiler doesn't need to know about the registry at all. Added minimal stubs in base.lua so ZIL modules loaded without bootstrap still work. Commit: 053ba00

[Copilot]

@copilot You'll need to modify compiler to emit SETG and GETG and add these functions to bootstrap

Already done in 053ba00: SETG(name, val) and GETG(name) are defined in bootstrap.lua, and the compiler now emits SETG(%q, val) for both <GLOBAL> and <SETG> forms. Minimal stubs are also in base.lua for environments loaded without bootstrap.