1.4.1 — the audit's four fixes

Batch A of the plan: the audit's four fixes, all verified on the artifact rather than the build tree.

Fixed

• The compressor had no inflate cap of its own. The three container transforms capped inflation at a flat 4 GiB and the compressor allocated up to it, while the decompressor has always used a relative cap. A 28,971-byte .zst inflating to 900 MB took the old build down; it now declines and stores the stream opaquely, peaking at 524 MB instead of asking for 4 GiB.

  The cap is max(input × 4096, 256 MiB) in all three — the decoder's policy with a floor, so a 6 KB stream inflating to 200 MB (a tar of zeros) still transforms, and anything past it is declined rather than allocated.

• Base64 offered itself on a binary scanned PDF. The detector accepted any single run of 32 alphabet bytes, and a PDF dictionary supplies one; on a 7.4 MB scan that produced layers 0x10 and a wasted trial. It now requires the alphabet to cover at least 1/64 of the file — a real base64 file still fires, a 32-byte accident in 7 MB does not.

• A short encode now reports itself. brotli_wrap and zstd_wrap relied on the re-encode verifier to notice a stream that never reached FINISH. Both now say so where the cause is known, rather than leaving a truncated buffer to be diagnosed three functions away.

• expansion_cap is saturating rather than wrapping. It multiplies an attacker-supplied true_size; the old wrap rejected by accident, and now it cannot wrap at all.

Added

• A marker convention. TODO(name-date): what and why, documented in BUILD.md, with the six catch (...) blocks that swallow everything marked. There were zero markers in 12,460 lines before this, which is why the audit found three things a grep should have.

Checks

37 suites, 53 CLI assertions, CI green. Checked on the artifact itself: the 900 MB bomb declines at 524 MB peak, a real base64 file still sets layers 0x10, and a FLAC still gets no BCJ.

Format unchanged at v8; nothing here alters a stream's meaning, so 1.4.0 archives read identically.