Prepare for FreeDOS package submission

- Add CHANGES.TXT with full version history (DOS-friendly format)
- Add DOS/FreeDOS section to README.md
- Move compiler memory safety and DOS target to Completed in roadmap
- Add hal_dos.c to architecture.md module map
- Add .tab-color to .gitignore

.gitignore

@@ -6,6 +6,7 @@ docs/_build/
 *.exe
 *.err
 *.lib
+.tab-color
 gwbasic_*.txt
 gwbasic_*.dat
 gwbasic_*.bas

CHANGES.TXT

@@ -0,0 +1,77 @@
+GW-BASIC 2026 -- Change History
+================================
+
+v0.17.0
+  - Compiler memory safety: --warn (static analysis), --safe (checked
+    integer arithmetic, enhanced array/GOSUB diagnostics), --safe=sanitize
+  - 16-bit real-mode DOS target (Makefile.dos16): 128KB standalone MZ
+    executable, no DOS extender required, far-heap TUI screen buffer
+  - 32-bit DOS/4GW target (Makefile.dos): 175KB LE executable
+  - Tested on FreeDOS 1.4
+
+v0.16.0
+  - AOT compiler: 69/69 tests pass (100%)
+  - CHAIN/COMMON/RUN "file" via runtime delegation
+  - Token embedding, string comparison, division-by-zero detection
+  - Compiler optimizations: constant folding, dead code elimination,
+    FOR step=1 elision, fast-path expressions, selective variable sync
+  - Cross-compile to DOS with OpenWatcom (24/24 files)
+
+v0.15.0
+  - Hardware I/O simulator (8253 PIT, PPI speaker, CGA, game port)
+  - 100% token coverage (all 144 GW-BASIC tokens)
+  - String space pool with compacting garbage collector
+  - Jupyter notebook kernel (Sixel graphics, INPUT, Pygments)
+
+v0.14.0
+  - MBF binary file compatibility (IEEE<->MBF at save/load boundary)
+  - Fix binary loader null-byte truncation
+  - DRAW M/S/A bug fixes, TA/=var;/X substring support
+
+v0.13.0
+  - VIEW/WINDOW/PALETTE graphics, PMAP function
+  - MBF float format for CVS/CVD/MKS$/MKD$
+
+v0.12.0
+  - BSAVE/BLOAD, TUI ANSI 16-color rendering
+  - CGA graphics framebuffer PEEK/POKE, keyboard shift flags
+
+v0.11.0
+  - DEF SEG / PEEK / POKE virtual memory
+  - GET/PUT graphics sprites, PRINT USING fixes
+
+v0.10.0
+  - Binary tokenized SAVE/LOAD, INKEY$ extended keys
+  - Golden-file regression tests, classic BASIC programs
+
+v0.9.0
+  - EDIT statement, ON TIMER/ON KEY event trapping
+  - F-key escape parser fixes
+
+v0.8.0
+  - Dynamic TUI screen buffer, --full flag
+  - LPRINT/LLIST with --lpt
+
+v0.7.0
+  - AUTO, RENUM (with GOTO/GOSUB patching), DELETE, COMMON
+
+v0.6.0
+  - DATE$/TIME$/TIMER, FILES, SHELL, CHDIR, MKDIR, RMDIR
+
+v0.5.0
+  - Full-screen TUI editor, KEY statement, Ctrl+Break
+  - Sixel graphics, SOUND/BEEP/PLAY
+
+v0.4.0
+  - CHAIN, RUN "file", random-access I/O (FIELD/PUT/GET)
+  - CVI/CVS/CVD/MKI$/MKS$/MKD$
+
+v0.3.0
+  - File I/O, PRINT USING, SAVE/LOAD, MID$ assignment
+  - Graphics stubs
+
+v0.2.0
+  - Variables, arrays, program storage, control flow
+
+v0.1.0
+  - Expression calculator with direct mode

README.md

@@ -116,6 +116,18 @@ bash tests/run_tests.sh              # interpreter
 python -m gwbasickernel.test_kernel  # Jupyter kernel
 ```
 
+## DOS / FreeDOS
+
+Cross-compiles to DOS with OpenWatcom V2:
+
+```bash
+wmake -f Makefile.dos16   # 16-bit real-mode (128KB standalone, no extender)
+wmake -f Makefile.dos     # 32-bit DOS/4GW  (175KB, requires DOS4GW.EXE)
+```
+
+The 16-bit build runs on FreeDOS, MS-DOS, and compatible systems without
+a DOS extender.  See [Getting Started](docs/getting-started.md) for details.
+
 ## Documentation
 
 Full Sphinx documentation in `docs/`:

docs/architecture.md

@@ -54,7 +54,7 @@ HAL writes straight to stdout.
 | AOT compiler analysis | `analysis.c` | -- |
 | AOT compiler codegen | `codegen.c` | -- |
 | Compiled program runtime | `gwrt.c` | -- |
-| Platform abstraction | `hal_posix.c` | OEM*.ASM |
+| Platform abstraction | `hal_posix.c`, `hal_dos.c` | OEM*.ASM |
 
 ## Source Layout
 

docs/roadmap.md

@@ -64,17 +64,32 @@ model with sentinel protocol.
 
 Install: `pip install -e . && gwbasickernel-install --user`
 
-## Next Up
+### Compiler Memory Safety (v0.17.0)
 
-### Compiler Memory Safety (`--warn` / `--safe`)
-- **`--warn`** -- static analysis warnings (uninitialized variables, GOTO to
-  nonexistent line, unreachable code, FOR/GOSUB nesting depth)
-- **`--safe`** -- runtime safety checks in generated C: checked integer arithmetic
-  via `gw_int_add/sub/mul` (fixes int16_t overflow UB), enhanced array bounds
-  diagnostics with line numbers and variable names, GOSUB stack overflow
-  diagnostics, string pool GC pinning
+`--warn`, `--safe`, and `--safe=sanitize` flags for the ahead-of-time compiler.
+
+- **`--warn`** -- static analysis: uninitialized variables, GOTO to nonexistent
+  line, unreachable code detection.  Zero runtime cost.
+- **`--safe`** (implies `--warn`) -- checked integer arithmetic via
+  `gw_int_add/sub/mul/neg` (raises Overflow instead of wrapping), enhanced
+  array bounds diagnostics with variable names and line numbers, GOSUB stack
+  overflow diagnostics, ABS/SGN type-preserving codegen, string pool GC pinning
+  infrastructure
 - **`--safe=sanitize`** -- above plus `-fsanitize=address,undefined` passed to gcc
 
+### DOS / FreeDOS Target (v0.17.0)
+
+Cross-compiles to DOS using OpenWatcom V2.  Two targets:
+
+- **16-bit real-mode** (`Makefile.dos16`): 128KB standalone MZ executable,
+  MEDIUM memory model, far-heap TUI screen buffer, no DOS extender required
+- **32-bit DOS/4GW** (`Makefile.dos`): 175KB LE executable, flat memory model,
+  requires DOS4GW.EXE extender
+
+Tested on FreeDOS 1.4 via QEMU.
+
+## Next Up
+
 ### Compiler Optimization Flags
 - **`--no-gc-check`** -- skip `gwrt_check_line()` per-line calls (no string pool
   GC, no Ctrl+Break check) for maximum throughput