asm/c/py: add (load), ports, write-file/file->string — full cross-impl parity
Asm gains the file I/O surface Python and C already had, unlocking
9/9 cells of the portal producer×consumer matrix (previously 6/9).
asm:
- (load "path") — mmaps file, swaps input source, loops scheme_read+eval,
restores on exit. Nestable. Uses SYS_LSEEK + SYS_MUNMAP.
- Output ports: (open-output-file), (close-port), (port?). Encoded as
SPECIAL values ≥ 1000 (fd = (val>>3) − PORT_SPECIAL_BASE), no tag-bit
expansion needed.
- (display), (write), (newline) accept optional port arg; printer
writes via output_fd global, swapped by port-aware builtins.
- (write-file path content) / (file->string path) — bytes in/out.
c, py: (write-file) / (file->string) added for parity.
tests: 131 asm (up 23), 189 functional (up 8, shared py+c),
tests/portal-cross-test.sh exercises 3×3 save×load matrix.