libc review: mem/, stdio/, fixes in sprinter-cc and FILE shim

libc/mem/:
  • Split bank_io.c into bank_io_w3.c (existing W3 helpers, base 0xC000,
    port 0xE2) and bank_io_w1.c (new mirror through W1, base 0x4000,
    port 0xA2).  Two .rel files so DCE picks only the needed group:
    a W3-only user pulls ~70 bytes instead of all 134.  W1 variants are
    `--memory tiny`-only (any other mode runs code from W1 or uses W1
    for the banked-code segment, swapping it crashes).
  • mem_alloc.c: add CF=err checks for mem_free_block and mem_get_page
    (were silently ignored), per-function docstrings on alloc/free/
    get_page/info, drop the confused "wait wrong order" comment in
    mem_info.  Header sprinter_mem.h gets matching per-function doc.

libc/stdio/:
  • Add hex_print.c (hex8/hex16/hex32, ~26 bytes) and dec_print.c
    (dec8/dec16/dec32, ~170 bytes) ported from solid-c STDLIB.ASM.
    Replaces the printf("%u"/"%X") wrappers in solid_helpers.c that
    dragged in the 3-5 KB printf machinery.
    - hex* use the classic cp 10 / sbc 0x69 / daa nibble→ASCII trick;
      hex8 self-calls for the high nibble, hex16/hex32 tail-call hex8.
    - dec32 is the master routine; dec8/dec16 jump into shared entry
      points (__dec_entry3 / __dec_entry5).  32-bit subtract-power-of-10
      keeps the high 16 bits in HL alt (shadow set).
    - DISCOVERY: ESTEX PUTCHAR ($5B) on our Sprinter build preserves
      the main register set + IX but CLOBBERS the shadow set
      (BC'/DE'/HL').  solid-c's original code assumed otherwise and
      garbled output for values ≥ 6 digits.  Fix: save/restore HL alt
      around the RST 10 in _dec_emit_or_skip.  Documented in
      memory/estex_putchar_abi.md.
  • file.c: drop stdaux/stdprn (no Sprinter printer API), change
    stdin/stdout/stderr fd markers to 0/-1/-2 (positive fds clash with
    ESTEX OPEN return values), add TODO header pointing at v2 buffered
    FILE rewrite (see docs/TODO.md for the Solid-C reference struct).

bin/sprinter-cc:
  • --memory big and --memory huge now always use crt0_banked.s (was:
    only with --bank flags), matching docs/memory_modes_implemented.md.
    When the user has no --bank flags, generate a tiny stub with
    `const uint8_t n_banks = 0;` and assemble bank.s for _bank_pages.
    Without this fix, openenv with --memory big could not see the
    estex_file_handle symbol exported by crt0_banked.

examples/openenv:
  • Add usage of estex_file_handle to confirm the crt0_banked startup-
    info is reachable.  Local extern decl — keeps the symbol out of
    sprinter.h since it only exists in big/huge builds.

examples/dec_test:
  • New regression test covering hex8/16/32 and dec8/16/32 across the
    interesting boundary values.

.gitignore: add .kilo/ (editor session cache).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/TODO.md

@@ -255,6 +255,43 @@ User-задаваемые ISR через Z80 IM 2 mode.  Нужны для:
 
 ### Прочие крупные пункты для v2
 
+- [ ] **FILE API rewrite — buffered streams** — текущая реализация в
+  `libc/stdio/file.c` это provisional unbuffered shim (каждый fputc/fgetc
+  = один read/write syscall).  Нужна полноценная buffered семантика
+  как в Solid-C:
+
+  ```c
+  typedef struct {
+      uint   flags;     // +0..1   file status flags
+      int    level;     // +2..3   empty/fill level of buffer
+      char  *curp;      // +4..5   current active pointer
+      int    fd;        // +6..7   underlying low-level fd
+      char  *buffer;    // +8..9   data transfer buffer
+      char   hold;      // +10     ungetc byte if no buffer
+      short  token;     // +11..12 reserved
+      char   dummy;     // +13     reserved
+  } FILE;
+  ```
+
+  stdin/stdout/stderr — fd-маркеры `0 / -1 / -2`.  Отрицательные для
+  stdout/stderr выбраны намеренно: ESTEX OPEN может вернуть positive
+  small fd (1, 2, …) для обычного файла → если бы stdout=1, реальный
+  fd=1 сталкивался бы с идентификатором.  fd=0 для stdin безопасно
+  (ESTEX 0 не возвращает).  Сами fd не передаются в syscall'ы —
+  диспетчеризация по флагам `_F_CONIN/_F_CONOUT`.
+
+  Принтер-потоки (stdaux/stdprn) НЕ реализуем — Sprinter принтерной
+  API не имеет.
+
+  Альтернатива — взять реализацию из third_party/solid-c (sources в
+  `SRC/CLIB/`); там есть готовый buffered FILE + fopen/fread/fwrite/
+  fseek/setvbuf и т.д.  Адаптировать к нашим open/read/write/lseek.
+
+  При rewrite заодно решить deferred issues stdio-review:
+  - `fwrite` short-write должен ставить `_F_ERROR`
+  - `fgets(buf, 1, fp)` — стандарт говорит "empty string", мы вернули NULL
+  - `mode_to_flags` — break-out на '+' (cosmetic)
+
 - [ ] **Audio API** — AY-3-8910 + COVOX через прерывания (требует IM2)
 - [ ] **ISA-8 slot support** — ZX-Bus карты (sound, network, etc.) — требует IM2 + чтения portов