# MP3 Encoder Build Provenance

## Current distributed runtime

ZoneBuilder's `mp3.wasm` is now built directly from its recipient source package.
It is **not** the historical npm WASM. LAME and the JavaScript wrapper were not
upgraded, and the published wrapper/C bridge source is unchanged.

- LAME: **3.100**, revision `98db548e8e851defbba3184125ce10725355c332`.
- Wrapper/bridge: **wasm-media-encoders 0.7.0**, revision
  `4a45333baadbab312d1cc0911151dfad23157c51`.
- Artifact build identity: **lame-3.100-wasm-a1d8ba08c80e**, built 2026-09-20.
- Runtime WASM: **132,969 bytes**; SHA-256
  `a1d8ba08c80ec5e63d62ad30685e9656c9032126e9cd3b9c95991f8e17083b68`.
- Unchanged JS wrapper: **5,887 bytes**; SHA-256
  `dd4e17abf5377dfecc726d6ec5e7b72dab01cf3522974278e5347f4e68480fb3`.

## Exact source → build → runtime

[Current source download](source/zonebuilder-mp3-source-0.7.0-lame-3.100-zb1.tar.gz):
**1,585,342 bytes**, 372 files; SHA-256
`1db1c9f00f5c50dc68c77ad0721228a8c9eb0b27a1463eeb98eb508a471ce034`.

The archive is the prepared source package with updated documentation/provenance;
all source, wrapper, bridge, build inputs and `rebuild-mp3.py` are unchanged from
the prior package. Its original upstream identities are verified by npm gitHead,
Git submodule gitlink, pinned source archives, and per-file SHA-256. Its
[manifest](source/manifest.json) separates historical published references from
current runtime artifacts; the archive hash is outside the archive to avoid
circular provenance.

From a fresh extraction with the recorded SDK environment active:

```sh
python3 rebuild-mp3.py --metadce "$EMSDK/upstream/bin/wasm-metadce"
```

Output: `wasm-media-encoders/wasm/mp3.wasm`. The helper does not download,
install, upgrade or modify upstream source. It preserves the exact production
flags and MP3-only configure/link/export-pruning inputs. It retains generated
object files, `libmp3lame.a` and the full/intermediate WASM for relinking.

The recipe statically links LAME and MIT `lame_enc.c`, using `-Oz -flto`,
`--strip-all`, `emmalloc`, memory growth, standalone WASM and the original
`minify_graph.json`. Configuration disables shared libraries, decoder,
frontend, dependency tracking, GTK tests and analyzer hooks. The explicit
`wasm-media-encoders-0.7.0` macro is the exact result of the original Yarn
version printer; rebuilding the unchanged JS wrapper is unnecessary.

## Recorded reproducibility toolchain

| Tool/input | Exact identity |
| --- | --- |
| SDK release label | Emscripten **2.0.8**, official mapping `e4ed6c79f4db8b175d9bbe55869b697aba9bcf2a` |
| Actual embedded compiler | emcc **2.0.7**, commit `d059fd603d0b45b584f634dc2365bc9e9a6ec1dd`; known upstream SDK-label mismatch |
| LLVM | clang **12.0.0**, commit `1a7a9efec3cf872dcf3e1a6e6fe39e797c4d9fc6` |
| Binaryen | wasm-metadce **98**, `version_97-120-gb8b457dda` |
| Node | **12.18.1**, the SDK's recorded runtime |
| Python/host | Python **3.9.6**; macOS Darwin 25.3 arm64, Rosetta for x86-64 tools |
| SDK archive SHA-256 | `85f25c13eb11fe263cbb23c1ff12732da0d14b1fbc528d58b3fb4d61d60b8332` |
| Node archive SHA-256 | `80e1d644fe78838da47cd16de234b612c20e06ffe14447125db9622e381ed1ba` |

Exact tool download URLs/hashes are in the extracted README and the
[reproducibility evidence](source/REPRODUCIBLE_BUILD.json). Use the recorded
compiler/runtime rather than modern Node: Node 24 fails this SDK's configure
probes. Reproducibility is verified for this toolchain/platform, not promised
for arbitrary compiler versions. No compiler or dependency was installed into
the application repository.

The repository's `third-party-source/lame-3.100/verify_rebuild.py` provides a
focused fresh-extraction build test. It checks the archive/member hashes,
executes the packaged helper, compares output bytes with the current runtime,
and writes success/failure evidence. It refuses a nonempty working directory
and never deletes prior work. The evidence records the exact command and tools.

## Delivery and replacement

The worker and service metadata use the WASM's full SHA-256 query identity.
The service worker maps only the old, unversioned MP3 WASM URL to that current
identity, including offline cache lookup. It never falls back to historical
unversioned bytes. Existing authentication safeguards, Lab JS/CSS no-store
handling and other cache policies are unchanged. No broad cache generation or
product build bump was made.

An existing installation must activate the updated service worker through the
normal update flow and reload; already-running encodes are not replaced in
place. Tests cover a fresh Lab page, historical cached bytes, a legacy worker,
reload, and offline use of the new cached WASM.

The source download has a new `-zb1` filename to avoid serving a previously
cached source archive. System → About → Third-Party Software links directly to
it. It is served under the existing `docs/` deployment boundary, never imported
or precached. The original source package remains available as historical
material. Future deployment must include the new archive, manifest, evidence
and notices; no remote publication occurred in this task.

## Historical reference only

The retired npm WASM was 132,999 bytes, SHA-256
`85e81719250b9a667b1258143f689dda70e3e57a7e7c29ab0b4cef65c8f6eb9a`.
It remains in the source archive's `reference/mp3.wasm` solely for comparison.
It is not ZoneBuilder's current runtime. Earlier functional-relink evidence is
retained in [RELINK_VALIDATION.json](source/RELINK_VALIDATION.json) as historical.
The original publisher's exact build environment need not be reconstructed:
the current runtime's source/build/output chain is directly verified.

Licenses, copyright and recipient modification/relink rights remain in the
[third-party notice](THIRD_PARTY_NOTICES.md). Library GPL v2-or-later remains
applicable to LAME; the wrapper remains MIT. This is not legal certification.