# Session save — to be continued

Date: 2026-10-02. HEAD: `7dbd516` (`express-draft-v1`). Tree clean.

## Where we are

`src/compiler/` holds the re-read compiler: `COMPILER/SCANNER/ERRORS/CODEGEN`
fully renamed + verified clean of numbered identifiers; `SYMTAB.MOD` draft v1
(988 lines, 27 FIXMEs); `EXPRESS.MOD` draft v1 (1489 lines, 137 FIXMEs, 20
FORWARD work-list helpers); `SYMTAB.DEF` expanded (words 10–27); `FRONTEND.md`
export map incl. newly found EXPRESS internals; `docs/compiler/` analysis.

## How we work

* Upstream dirs git-ignored; only `docs/`, `src/`, `SUMMARY.md`, `SESSION.md` versioned.
* Decompile in parallel background workers (3–4 groups per module), each returns
  Modula-2 with `{/* offset */}` comments; assemble + normalize via script
  (`Compiler.word6–26`, `Scanner.word2–12`, `Doubles.proc5–11` mappings);
  verify with `grep -nE '\b(param|local|global|proc|PROC)[0-9]+\b'`.
* Drafts are unverified by design: MCD `unassemble.c` diff still pending for all.
* Commit per step, tag per milestone (`*-v1`).

## 2026-10-03: audit + proc32 applied (`audit-01`)
proc32 WriteOutputFiles added; 8 SYMTAB + 9 EXPRESS signature swaps applied
(def headers; bodies/calls positional-consistent by construction); STMT+PASS1
all KEEP; D1/D2 resolved (map stands); CappedStrLen=StrLen alias noted.
Next: GENZ80 recon + MCD-diff verification harness.

## 2026-10-03: GENZ80 recon + MCD-diff harness (`genz80-harness-01`)
GENZ80: no binary/disassembly anywhere (only call site + overlay-table
strings); trigger chain partly open (no setter of nativeCodeRequested found);
recovery = extract overlay from original CP/M media. Harness tools/mcdiff.sh:
stage 1 green (1a clean, 1b FORWARD-OK, 1d spot-check; fixed StrLenHelper,
word6, Doubles.proc5, Scanner.word2, Compiler.word3 leftovers on the way).
VM builds clean (gcc, `m2` binary); stage-2 run blocked on terminal I/O
(documented pty approach in mcdiff.sh header).
Next: GENZ80 media hunt; stage-2 pty-driven MCD diff per module.

## Next steps (in order)

1. DONE (`statemen-draft-v1`): `STATEMEN.MOD` 830 lines + frame-mechanics proof.
2. DONE (`pass1-draft-v1`): `PASS1.MOD` 981 lines; disputes D1-D4 + proc9 recorded.
2. Pass1 bodies (`pass1.txt`, 2975 lines): `~ParseType` (02e6), `ParseRecord`,
   formals, decls, module heads, `WriteSym` — 3–4 workers.
3. Resolve `SYMTAB.MOD` FIXMEs (AllocSym arity, D-group sketches, LSL) and
   `EXPRESS.MOD` FORWARDs (CentralError/PushOperand/EmitOp/BoolCondHelper/...).
4. `GENZ80` native backend (untouched so far).
5. Recompile + `unassemble.c` MCD diff verification for every draft.
6. Refresh `SUMMARY.md` + retag when milestones land.

## SCANNER verify checkpoint (2026-10-06, uncommitted -> committing)
- SCANNER.MOD compiles on v1.00 (2760 bytes): OOM cliff bisected to
  `FLOAT((decVal + LONG(1)) DIV LONG(2))` expression heap spike; fixed with
  `1L`/`2L` literal folding (identical codegen, proven T3d probe).
- MCD diff vs Reloaded SCANNER.MCD: 34/41 mnemonic-identical (00-gap
  stripped, absolute targets masked). Remaining 7 fully accounted:
  proc23/24 clean-room (hand-tuned M-stack code has no v1.00 source form;
  algorithms decoded + restored incl. c=TRUE fold branch the decompiler
  dropped), NUMBER 4-mn literal-fold trade (forced by OOM fix),
  proc37 tail = next-proc boundary attribution (35/35 prefix identical),
  COMPIL prologue = VarAddr shim `nested_call proc40` (module VarAddr
  exists nowhere; open-array shim proven), proc40 = original Z80 asmcode
  blob vs shim, proc0 = 2-op stub identical (rest is gap slack).
- StrLen signature now `(s: ADDRESS; bound: CARDINAL)` matching original
  DEF proc24 slots (WORD->CARDINAL: v1.00 WORD has no comparisons);
  SYMTAB.MOD:221 caller fixed to pass bound 128 (proven from symtab.txt
  `load immediate 128` at call site); CODEGEN.MOD:392 already 2-arg.
- Padding blocks removed (Allocate/FindIden/NextCh/ScanNext) — were dead
  code polluting the diff; GetSym now byte-compares modulo gap zeros.

## CODEGEN verify checkpoint (2026-10-12)
- CODEGEN.MOD compiles on v1.00 (2393 bytes): 34/37 mnemonic-identical.
- Stale renames fixed (codeBuf/EnterMod/ScanErr). keywordTable saga closed:
  original COMPILER.MOD also Allocate+CARDINAL-stores (proven byte-shape),
  CODEGEN reads low byte via `limit_check+shl1+LXB` = `compTab[i][0]` shape;
  v1.00 can't spell that from ADDRESS global, so local 2D-BYTE overlay
  (Q1/Q2-proven ADDRESS:=pointer assigns) at 2 use sites, +2mn each.
- proc0 trailing region = embedded absolute-address tables shifted by the
  +6 growth (every byte -4): consequential, not semantic.

## SYMTAB WIP checkpoint (2026-10-12, uncommitted -> committing as WIP)
- SYMTAB.MOD compiles through GetAttr, dies inside EnterIdent (heap).
- Banked fixes: TryCompile = savedEditPos>savePos (saveErr was fiction);
  allocHook (COMPILER.dword27, appended last); word8=scopeChain,
  word9=currentScope, SYMTAB.proc7=RestoreAfterEdit; transfer-index/deref
  bans -> Words-view params + temps; `= 0`/`CHR(ORD())`/`ORD()` zero-cost
  adaptations; unclosed comment @254 (pre-existing) fixed; DEF-leak
  (Files/ADDRESS) + DEF-FORWARD collisions fixed; impl-var abbreviations.
- OOM masks type errors (VAR-mismatch, Allocate(ADR()) both OOM) — always
  isolate suspects in fresh-heap ZZ probes. Nesting depth tips razor-margin:
  flat IF+call passes, same content nested OOMs; ELSIF chain flattened.
- Identifier chars/comments/slots/forwards all FALSIFIED as heap drivers
  (5604-char truncation ~1 proc; 17KB comment strip zero; +12 dummy forwards
  fit). Standing theory: per-scope node budget; Borland wrote smaller
  statements. Names/chars exonerated — readability preserved.
- Drive holds full chain (COMPILER.SYM now WITH allocHook); ZZ probes
  (W1-W8, U1-U2, V1-V4, T1-T5, B-series, F1, M1, E1-E2, P1, S1-S6, Q1-Q3,
  H1-H2) document v1.00 codegen rules. tmp/ ignored by git (local only).

## Next session plan
1. Fold EnterIdent's `IF >= 5` guard into single-depth `AND` (or split the
   arm); recompile; expect UnlinkScope/InitHeaps next.
2. Same isolate-and-flatten loop per proc to end of SYMTAB.MOD; full MCD
   diff vs Reloaded SYMTAB.MCD; commit; tag `symtab-verify-01`.
3. Then EXPRESS (1490 lines, biggest risk) → STATEMEN → PASS1 same loop.
   Budget for ZZ probes: each suspect construct gets a fresh-heap probe
   BEFORE bending src around it.
4. If a module genuinely exceeds retail heap with clean nodes: timebox 2h,
   then switch to vm_linux instrumentation (heap high-water log) for ground
   truth instead of blind bisection. Do NOT rename everything terse.
5. Refresh SUMMARY.md + retag at each verify tag.

## SYMTAB session 2026-10-07 (EnterIdent heap wall)
- GetAttr arms 101/102: dropped writebacks + `sub` local, reuse `new`
  (original tail-calls with `jump_stack`: result discarded, memoization is
  the effect). EnterIdent arm3: nested IF/ELSE -> two single-depth AND-IFs.
  Neither fixed the OOM (kept: both are the honest minimal shapes).
- Heap-model verdict after full falsification battery (names, chars,
  comments, slots, forwards, locals-count, prefix-size, ASCII, $[-retention,
  nesting): budget is per-proc NODES; EnterIdent needs ~10 nodes over budget
  with every retail-legal spelling exhausted (all 6 temp-assigns proven
  mandatory: transfer-index/deref bans, VAR-formal bans).
- VERSION SKEW (decisive context): retail M2.COM = "Version 1.00", writes
  SYM v3; shipped originals carry SYM v2 (Borland-internal/older toolchain).
  Only v1.00 retail on hand (other M2.COM is a different vendor product).
  Explains laxer-original spellings (direct ADR pushes, `ADR->VAR`,
  Buf->Identifier) that retail rejects or OOM-masks.
- Conclusion: big modules (SYMTAB/EXPRESS/STATEMEN/PASS1) cannot compile
  under v1.00-retail heap with faithful sources. Next: vm_linux path —
  build the portable M-code VM, run retail m2.ovr under instrumented
  mcode.c (heap high-water log) for ground truth; heap size does not affect
  emitted code, so verification stays sound. Fallback: partial (prefix)
  verification, honestly labeled.

## SYMTAB session 2026-10-07 (prefix verification via stub-tails)
- Stub-tails method works: stub bodies from EnterIdent on (+7 DEF-stub
  HALTs), keep headers -> v1.00 emits MCD (1059B). Full module still OOMs
  in EnterIdent (unchanged wall).
- Our MCD retains 6-char uppercase names (no directive); originals are
  numbered -> FINAL SYMTAB needs explicit `$[+ remove` (+ `$[-` for IMDCLS).
- Prefix score (leave-truncated, jumps masked): 2/12 SAME* (MatchSym,
  EnterChained). Rest diverge STRUCTURALLY (inverted conditions, extra
  leaves, +30mn in PutAttr) = draft-v1 group-guess quality, not heap
  artifacts. Notably ours runs LONGER everywhere (temps), orig is leaner.
- Inter-proc gap filler differs by toolchain (orig `...ff`, ours `...00`),
  excluded from scoring like dep-slots.
- Next: re-read prefix bodies (PutAttr/GetAttr/AllocSym/FindModule first)
  against symtab.txt statement-by-statement; keep heap discipline (flat,
  minimal nodes). VM path still open for full-module compile.

## SYMTAB session 2026-10-07b (nesting model + record views, prefix 7/14)
- CALL GRAPH (mnemonic-authoritative, unassemble.c): `ee`=sibling/self display
  call (ZZ-proven under v1.00), `ec`=downward (parent->nested child), `ed/f/ef`
  = display-free. FORCED nest map: AllocSym{CheckNode,NewString,PutAttr},
  EnterIdent{GetName,GetAttr}, CompileDispatch{35,36,37/TryCompile}, + {32}@2,
  {34}@33, {38}@6, {25}@24, {27}@26, {29,30,31}@28. Rest top-level. Gap-`ff`
  bytes decode as phantom calls — ignore trailing-ff "calls". proc16 dead.
- Restructured SYMTAB.MOD accordingly (nested, forwards trimmed to the 2
  cycle-breakers). v1.00 emits ee/ec exactly like the original. Zero-cost:
  transfers emit no code; view-field TYPES are byte-neutral (all 1-word).
- Record-field views (LSW/SSW) replace Words indexing (LXW) everywhere:
  new local Entry type (CARDINAL/WORD/BITSET per dominant use); T1 direct
  for nodes. Proven: `i * 16` folds to `shl` (v1.00 peephole — swap all
  `N * x` with power-of-2 N); open-array actuals push HIGH (GetName view
  is [0..128], not [0..127]); declared exceptions emit small codes
  (NodeErr=273 vs orig 272, 1B documented); `ADDRESS<CARDINAL` etc. need
  CARDINAL() views; LSWn pops base (Indirect.mod); `=` on arrays = inline
  string_comp with (addr,size) pairs.
- Prefix score 7/14 exact (FINDMO/ENTERM/LOOKUP/MATCHS/NEWSTR/ENTERC/GETNAM).
  CHECKN=1B (exception code). Left: PUTATT/ALLOCS/GETATT detail (frames,
  guard polarity (accepted peephole class), leave-vs-jump (heap-driven flat
  kept), stack-threaded temps (accepted)). ENTERI wall stands (full build).
- Slot map COMPILER.DEF re-verified 1:1 (systemScopeDesc=23 etc.).

## SYMTAB session 2026-10-08 (direct-VAR arms, FindExport out, 7/14)
- Recursive PutAttr arms now pass entry fields DIRECT as VAR (`PutAttr(e^.w5,
  T1(sv^.word5))`) + fixed SRC-vs-entry object bug (node part must be src's).
  GetAttr Entry views; PutAttr dedup loop is REPEAT (matches orig).
- FindExport moved top-level (no self-ee/frame use); ImportAll 19->13 locals
  via honest merges (sysAdr inline, matched/sib... no: matched->findIdx,
  caseFlag/importEvery inline, stoImp->sysImp, expIdx->scopeIdx). All remaining
  overlap. 13 typed minimum exceeds retail budget (~12 plain-equiv).
- PROVEN (6 ways): ImportAll region cannot compile under v1.00-retail
  (decl-count + record-descriptor weight; Borland heap ~2x). colCount-global
  and ListExports-out variants tested, both insufficient/worse. VM cannot
  raise heap (16-bit address space, high_mem already top).
- Prefix 7/14 exact (FINDMO/ENTERM/LOOKUP/MATCHS/NEWSTR/ENTERC/GETNAM).
  Left: PUTATT/ALLOCS/GETATT accepted-class gaps (frames, guard polarity,
  leave-vs-jump, stack-temps), CHECKN 1B, SYMBOL epilogue, ENTERI wall,
  SYMTAB tail by construction. Next: EXPRESS (same playbook per-proc).

## EXPRESS session 2026-10-08 (ground-truth verdict + compile groundwork)
- VERDICT (byte-proven): Reversing `express.txt` (module base 15a5) and
  Reloaded `COMPILE.DIR/EXPRESS.MCD` (base 17fd, 6303B) are DIFFERENT BUILDS
  of the same source family — NOT the same file. Same proc numbering, same
  dep table (7 deps incl DOUBLES), 20+ procs byte-identical (e.g. proc32
  43/43B), rest differs by small edits. Reloaded = newer (extra error
  strings " assignment", "this type"; front-proc growth +0x258 before
  old-proc4). Ground truth stays Reloaded MCDs (matches all verified
  modules + v1.00 runtime); REV txts are advisory only.
- Old-unassemble artifacts (do NOT chase): per-file address rebase
  (EXPRESS REV+0x258=ours; PASS1 REV+0x3F0; STATEMEN +0x0), missed procs
  (EXPRESS REV lacks 1,2,3,6,10,11,22-31 = walk bug, procs exist+are called),
  AAAAAA ghosts, `load (ix)` vs `load outer frame`, `65535` vs `-1`,
  `call_rel N` vs string-print spellings. Same-dialect (old-vs-old) +
  immediate-normalized fp is the honest comparator.
- PASS1 dep "skew" was a misread (truncated head): both show 11 deps incl
  LOADER. PASS1 old-tool output has 66 garbage heads (walk bug on that
  file); use new-tool disassembly as reference.
- Committed: EXPRESS.DEF (22 exports + Desc type), PASS1.DEF stub
  (CondInsert/InsertEntry BOOLEAN), MOD mechanical fixes (Desc->DEF,
  leak-rule imports, 29x comment markers). New EXPRESS procs (no draft
  coverage, decompile fresh): 1,2,3,6,10,11,22-31 (tiny predicates:
  proc25 opt-12 guard, proc26/23/24 kind predicates, proc6/22 cond-copy,
  proc27 TypeSizeOf callswitch). Genuine Borland helpers, not LONGREAL.
- Next: per-proc audit in MCD order; first fix IsOrdinal WORD>=0 via
  INTEGER view (MCD uses SIGNED igreater_or_equal on word5/word6).

## EXPRESS session 2026-10-08 (head model + nesting map + first blood)
- HEAD MODEL (proven): curDesc (global word2) is HeadPtr (5-word head:
  typ,mode,value,extra,kind) — 149 MCD accesses all fields 0-4, never 5+.
  Temp slots reserve 10 bytes; all copy blocks move 10 bytes (units are
  BYTES: R1/R2/R5/R10 -> 2/4/10/20). `y := x` (R10) = dest,src,20,copyblock.
  MOVE() is a separate opcode (not copyblock). Full descs (low/high) via
  full-typed params/locals; global never field-5+. curDesc never stored
  (link-time init). 220x curDesc^.raw[0..4] -> named fields; 6x raw[5]/[6]
  flagged FIXME-HEAD (draft misattribution, MCD audit pending).
- NESTING MAP (proven by call opcodes + fct_leave bit): ec=parent->nested
  child, ee=nested-self/sibling (call_with_frame), ed=same/up/top-sibling.
  Nested fns emit plain fct_leave (no 0x80 GP-restore); top-level get 0x80
  (ZZ programs always 0x80 — mask bit7 in ZZ-vs-MCD scoring!). Map:
  proc5>32, proc37>38, proc18>39>{40>{41,42},44,45,46,43}, EXPRES>48>49>50>51,
  ASSIGN>52(ghost?). Rest top-level. IsSet/IsOrdinal callers re-read (no
  phantom recursion: proc33 self-calls via ed).
- AUDITED (ZZ-verified shapes): IsOrdinal nested-in-PopExprDesc byte-exact
  (nested-IF + INTEGER() views for signed ige + RETURN TRUE=load 1);
  PopExprDesc (isOrd CARDINAL via ORD(), INTEGER() wraps, IntType not Card,
  mode:=2, ABS(INTEGER()) wrap, EmitStandardOp(0+ORD(neg)), OR-assign);
  IsSet single-OR + AddressType/CardType pairs (word7/8, +2 rule) + 96 IN
  BITSET(field); BaseTypeOf single-OR + WordType(word18) + CARDINAL(word3).
- Probes banked: INTEGER()/CARDINAL() zero-cost, ORD() zero-cost,
  CARDINAL->INTEGER assign OK, ADDRESS->RecordPtr OK, ABS needs INTEGER,
  CARDINAL/INTEGER mixed ops incompatible, H5Ptr(cur)^ transfer-deref banned.