v-TP3-DEAD-FIXTURES — Summary
=============================

Tag: v-TP3-DEAD-FIXTURES
Commit: 30f9fae

What changed
------------
- The 9 fixtures that compiled but never executed (t08_const, t09_if,
  t10_while, t11_for, t12_repeat, t13_proc, t15_label, t27_localvar,
  t28_farparam) were rewritten to print observable results. Their `.out`
  files were hand-derived from the Pascal semantics, never blessed from
  machine output. Each now has a behavioural counterpart.

Bugs found and fixed
--------------------
1. `ParseMul` used the same operator code as `+` (both 1). `*` therefore
   emitted ADD; constant folding hid it for constant operands. Now named
   `OpAdd/OpSub/OpMul` constants, so levels cannot collide. (t08 and a
   variable-multiply path)

2. `ParseCmp` had `>` and `>=` swapped: `9DH` = SETGE for `>` and `9FH`
   = SETG for `>=`. Boundary cases failed. Fixed, and each CASE arm now
   carries its mnemonic beside the hex.

3. `REPEAT…UNTIL` used `JNZ` to loop back (condition TRUE), so it behaved
   like `WHILE`. Now uses `JZ` → loop back while condition is FALSE. Verified
   by i:=0; repeat i:=i+1 until i>5 printing 6 (not 1).

4. Sibling procedures shared the same parameter namespace. `HideLocals`
   relabels a procedure's own symbols to `0FFFFH` on close (relabelled, not
   popped, because `symtab[old].resvar` holds an index). This prevents cross-
   procedure collisions and fixes the "two procedures both declare `a`" case.

Scope decisions and findings
----------------------------
- Parameter lists require commas; variable lists in this compiler require
  separate `var` declarations. `;` between params is rejected.
- A parameter may not shadow a global (DupTest rejects any name found).
- Call arity capped at 16 arguments; exceeding raises `ECompOvf` = 99.
- `EmJcc`/`EmSetcc` emit 386-only opcodes (`0F 8x`/`0F 9x`) on a 8086
  target; invisible to qemu-i386 (which defaults to post-386). Worth
  trying `-cpu 8086` as a future check.

Tests / harness
---------------
- `run_all.sh`: 12 checks ALL PASS.
- `nonvacuity.sh`: 39 ok / 0 failed (includes 5 new cases that mutate each
  of the four bugs back and require `run_com_exec.py` to go red on the
  exact fixture that pins them).
- Compile matrix: 33 passed / 0 failed.
- Execution: 30 passed / 0 failed.
- .COM linker: 30 checked / 0 failed.
- Runtime entries: 36 passed / 0 failed.
- `t28_farparam` references p63/p70 to exercise disp16 encoding but does
  not assert their runtime values (they are unpassed due to the 16-arg cap).
  *(Later `v-TP3-ARGORDER` milestone: the frame now follows TP3's "last
  declared parameter at BP+4" rule, so the same two offsets, +128 and +142,
  are read through `p8` and `p1`; the encoding this row is about is
  unchanged.)*

Tag placement
-------------
`v-TP3-DEAD-FIXTURES` points to 30f9fae (the work commit). An additional
tag `v-TP3-COM-IMAGE` was placed at 7dada57 (where Linker/ComTest first
appeared), because the documentation for that milestone was written later;
the reasoning is in the tag message. HEAD is 30f9fae, 17 commits ahead of
`origin/master`, nothing pushed.

What remains (next steps)
-------------------------
1. 8086 branch/compare lowering: rewrite conditional branches to TP3's
   `excond` + `JZ rel8` idiom (or try `qemu -cpu 8086` first to see the
   class turn red under an 8086 CPU model). Wide golden blast radius.
2. CmdRun (`R` key): in-process 8086 interpreter, cross-validated against
   qemu on the same images.
3. String variables (`s : string`, assignment, `writeln(s)`).
4. Nested procedures/recursion, `var` parameters (`SEG:OFF`), range/index
   checks, typed constants, array at use (`t14`), case subrange labels.
5. `readln` of a `BYTE` (separate `xrdbyte` / `TU_RdByte`).
6. Enforce the 4 KiB code window (error if `pc` reaches data start).
7. Harmonise multi-name declarations (both `,` and `;` spellings).
8. Harden program-header parameter loop against non-advancing input.
9. FreeDOS as a third opinion (untried).