feat(bgcode): heatshrink decompression (DD-011 phase 3) (#188) - #235
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Adds heatshrink (LZSS) decompression — windows 11 & 12, lookahead 4 — to the .bgcode decoder. With this, ALL four spec compression codecs (None/DEFLATE/heatshrink-11/heatshrink-12) and all encodings (None/MeatPack/MeatPack-comments) are decoded; a heatshrink-compressed GCode block now decodes end-to-end to plain G-code. The decoder is a TS port of the LZSS decoder from the ISC atomicobject/heatshrink (© 2013-2015 Scott Vokes), attribution preserved — no AGPL libbgcode (RR-003 §8). Wire format: MSB-first bit stream; tag bit (1=literal 8 bits; 0=backref of windowBits index + lookaheadBits count, each value-1); a backref copies count+1 bytes from index+1 back in a circular window, re-emitting each (self-referential runs supported). Validated against vectors built by an INDEPENDENT MSB-first bit-packer from the spec (literals, single + multi-byte backrefs, offset-2 interleaving, self-referential runs, window 11 & 12, a realistic repeated g-code fragment) + block-level integration through openBgcode. Output bounded (bomb defense). The stale phase-1 "heatshrink unsupported" test → an unknown-compression-id rejection. Real PrusaSlicer heatshrink files = phase-4 golden-equivalence. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
sobechestnut-dev
enabled auto-merge (squash)
July 27, 2026 20:27
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Phase 3 of the #188 bgcode epic (DD-011 §14). Does not close #188 — container-adapter integration + real-file golden-equivalence (phase 4) and the §7.3 review (phase 5) remain.
What
heatshrink (LZSS) decompression — windows 11 & 12, lookahead 4. With this, all four spec compression codecs (None / DEFLATE / heatshrink-11 / heatshrink-12) and all encodings (None / MeatPack / MeatPack-comments) are decoded. A heatshrink-compressed
.bgcodeGCode block now decodes end-to-end to plain G-code.Licensing — clean, attributed
A TypeScript port of the LZSS decoder from the ISC
atomicobject/heatshrink(© 2013–2015 Scott Vokes) — attribution in the source header. ISC is permissive/MIT-compatible; no AGPLlibbgcode(RR-003 §8).Validation — independent oracle
Vectors are built by an independent MSB-first bit-packer from the wire format (a separate code path from the decoder's reader), so
decode(pack(tokens)) === expectedchecks the decoder against the spec, not itself: literals, single- and multi-byte back-references, offset-2 interleaving (ABABAB), self-referential runs (copy length > offset), window 11 & 12, a realistic repeated G-code fragment, the bomb cap, and block-level integration throughopenBgcode. Real PrusaSlicer heatshrink files land in phase 4 for golden-equivalence.Verification
typeCheck✓,lint✓ (0 errors),docs:build✓ (3/3), CI-liketest:packages✓ (30 bgcode tests across 3 files),pack:check✓ (additiveheatshrink.*snapshot).🤖 Generated with Claude Code