CodeGen (`codegen.txt` 1746 lines, `CODEGEN.DEF/MOD`)

MCode emitter with peephole folding + 2KB sliding window on the output file (Scanner.global4) + fixup queue for jumps.

Opcodes: see CODEGEN.MOD const block (OPLLD=08H ... OPCALL=0EDH ...), consumed by MCode_specification/*.mod.

State

old	proposed
global2/3/4	`nextEmit/winBase/winLimit` (init 16/0/4096)
global5	`emitEnabled`
global6	`window[0..2047]` (`= ADR(Scanner.global21)`)
global7/8/9/10	`pendMode/pendSize/pendDisp/pendOff`
global11/12	`fixQueue[0..15]/fixCount` (`{kind,word1/word2\\|ptr\\|long}`)
global14/15	`pendFlag/checkOverflow` (`execute=4`)

Procedures (proposed)

old	proposed
Emit1/Emit2/EmitWord/EmitString	same (guard `OverflowGuard`, flush if full)
proc19/20	`PeekByte/PokeByte` (window or `SetPos+Read/WriteByte`)
proc23	`FlushWindow` (write 2048, slide tail)
proc28	`SeekWindow` (512-align, refill)
proc29	`OverflowGuard` (`nextEmit >= ComLine.codepos -> RAISE 281`)
proc26	`Assert`
proc22/24	`OpenEmit/InitCode`
proc4	`DiscardPend`
proc5/30/31/32	`SetPend/FlushPendOp/BaseOp/FlushQueue` (peephole: `LDIX/LONGREAL/LI/LB...`)
proc8/9	`QueueConst/QueueLong`
proc6	`EmitOp(sub,type)` (fold `NEG/power2/AND/EQ0`, types 0..5: long/short/DCOMP/REALCMP/set/extern)
proc7	`EmitExt`
proc10	`EmitStd` (`LIMIT` fold)
proc11	`EmitMisc`
proc17/18	`EmitSys/EmitExt3`
proc12/13/14/15/16	`OpenFix/CloseFix/InsertFix/AdjustFix/MarkFix` (short `224`-case vs word fixups)