Update Sphinx docs with string pool GC, remove string GC from limitations

docs/architecture.md

@@ -50,15 +50,16 @@ HAL writes straight to stdout.
 | Sound engine | `sound.c` | — |
 | Virtual memory (PEEK/POKE) | `virmem.c` | — |
 | Hardware I/O ports | `portio.c` | — |
+| String space pool + GC | `strpool.c` | GWEVAL.ASM (GETSPA/GARBAG) |
 | Platform abstraction | `hal_posix.c` | OEM*.ASM |
 
 ## Source Layout
 
 ```
-src/         — core interpreter (22 files)
-include/     — headers (14 files)
+src/         — core interpreter (23 files)
+include/     — headers (15 files)
 platform/    — HAL backends (1 file)
-tests/       — 71 automated test programs, 4 classic interactive programs, compat harness
+tests/       — 72 automated test programs, 4 classic interactive programs, compat harness
 docs/        — Sphinx documentation
 ```
 
@@ -96,7 +97,8 @@ algorithms are reimplemented in idiomatic C with modern data structures.
   at the binary save/load boundary and for file I/O (CVI/CVS/CVD, MKI$/MKS$/MKD$),
   matching the original's on-disk format
 - **Dynamic memory allocation** — `malloc`/`free` instead of a 64KB segment layout
-- **malloc'd strings** — instead of a compacting garbage collector
+- **String space pool** — 32KB contiguous pool with compacting GC at statement
+  boundaries, matching the original's GETSPA/GARBAG approach
 - **`setjmp`/`longjmp`** — for error recovery, matching the original's stack reset
   behavior
 - **ANSI terminal** — TUI uses ANSI escape sequences and alternate screen buffer

docs/development.md

@@ -18,11 +18,11 @@
 | 0.12.0 | | BSAVE/BLOAD, TUI ANSI 16-color rendering, CGA graphics framebuffer PEEK/POKE, keyboard shift flags |
 | 0.13.0 | | VIEW/WINDOW/PALETTE graphics, PMAP function, MBF float format for CVS/CVD/MKS$/MKD$ |
 | 0.14.0 | | MBF binary file compatibility (IEEE↔MBF at save/load boundary), fix binary loader null-byte truncation, fix DRAW M/S/A bugs, add TA/=var;/X substring |
-| 0.15.0 | | Hardware I/O simulator: OUT/INP/WAIT/MOTOR statements, port emulation (8253 PIT, PPI speaker, CGA mode/color, COM1, game port), continuous tone via PulseAudio. Fill remaining gaps: RESET, ENVIRON/ENVIRON$, ERDEV/ERDEV$, IOCTL/IOCTL$, LCOPY, DATE$/TIME$ assignment, CALL, COM |
+| 0.15.0 | | Hardware I/O simulator: OUT/INP/WAIT/MOTOR, port emulation (PIT, PPI, CGA, COM1, game port), continuous tone. Gap-fill: RESET, ENVIRON, ERDEV, IOCTL, LCOPY, DATE$/TIME$ assign, CALL, COM (100% token coverage). String space pool with compacting GC |
 
 ## Tests
 
-71 test programs in `tests/programs/`, plus 4 classic interactive programs in
+72 test programs in `tests/programs/`, plus 4 classic interactive programs in
 `tests/classic/` (Hamurabi, Lunar Lander, Gunner, Diamond from David Ahl's
 *BASIC Computer Games*).
 
@@ -32,7 +32,7 @@ Run the full automated suite:
 bash tests/run_tests.sh
 ```
 
-Each test has a 5-second timeout. 66 tests have `.expected` golden files
+Each test has a 5-second timeout. 67 tests have `.expected` golden files
 for output regression detection. Tests without golden comparison: datetime,
 on_timer, timer_stop (timing-dependent), color_test (visual), play_music
 (audio duration).

docs/index.md

@@ -27,7 +27,7 @@ version is structured as modular C suitable for new feature development.
 - **Printer output** — `LPRINT`/`LLIST` to file or real hardware via `--lpt`
 - **Classic programs** — Hamurabi, Lunar Lander, Gunner, and Diamond from
   David Ahl's *BASIC Computer Games* (1978) run out of the box
-- **71 test programs** with golden-file regression testing and DOSBox-X
+- **72 test programs** with golden-file regression testing and DOSBox-X
   compatibility testing against real GWBASIC.EXE
 - **MIT License**
 

docs/language-reference.md

@@ -30,6 +30,12 @@
 
 `EOF`, `LOC`, `LOF`
 
+## Memory Functions
+
+- `FRE(x)` — free bytes in the string space pool.  `FRE("")` triggers a
+  garbage collection pass before reporting; `FRE(0)` reports without collecting.
+- `VARPTR(var)` / `VARPTR$(var)` — variable address (internal index)
+
 ## Pseudo-variables
 
 `ERL`, `ERR`, `CSRLIN`, `INKEY$`, `DATE$`, `TIME$`, `TIMER`, `POS(0)`
@@ -225,6 +231,22 @@ The file format is compatible with the original GW-BASIC: byte 0 = `0xFD`,
 bytes 1-2 = segment (LE), bytes 3-4 = offset (LE), bytes 5-6 = length (LE),
 followed by the raw data bytes.
 
+## String Space and Garbage Collection
+
+All string data lives in a contiguous pool (default 32,768 bytes), matching
+the original GW-BASIC's string space architecture.  Allocation is a bump
+pointer; dead strings are reclaimed by a compacting garbage collector that
+runs automatically at statement boundaries when the pool is running low.
+
+```
+CLEAR ,8192             ' set string space to 8KB and clear variables
+PRINT FRE("")           ' trigger GC and print free bytes
+```
+
+`CLEAR n` (or `CLEAR ,n`) resizes the string space to *n* bytes and clears
+all variables.  `FRE("")` forces a garbage collection pass and returns the
+free bytes; `FRE(0)` returns the current free count without collecting.
+
 ## Hardware I/O (OUT / INP / WAIT)
 
 `OUT`, `INP`, and `WAIT` provide access to emulated IBM PC I/O ports, enabling

docs/roadmap.md

@@ -25,6 +25,11 @@ Also in v0.15.0: filled remaining statement/function gaps — `RESET`,
 `DATE$`/`TIME$` assignment, `CALL`/`CALLS`, `COM`.  All 144 defined
 tokens are now handled (100% token coverage).
 
+String space pool with compacting garbage collector (`strpool.c`),
+replacing individual `malloc`/`free`.  32KB default pool, bump-pointer
+allocation, compaction at statement boundaries.  `FRE()` returns actual
+free space; `CLEAR n` resizes the pool.
+
 ## Next Up
 
 *(Looking for the next major feature — see IDE and Notebook Integration below.)*
@@ -45,7 +50,6 @@ tokens are now handled (100% token coverage).
 
 ## Known Limitations
 
-- String garbage collection not implemented (uses `malloc`/`free` instead)
 - Maximum 256 variables, 64 arrays, 16 FOR nesting, 24 GOSUB nesting,
   16 WHILE nesting
 - `CALL`/`CALLS` (machine code execution) raises Illegal function call