feat: Add Audio8-ASR-0.1B community model port (audio8_asr)

[gqf2008]

Summary

Closes #336.

Native audio.cpp port of Audio8/Audio8-ASR-0.1B as community family audio8_asr: a compact multilingual offline ASR (en / zh / yue / ja / ko / fr / de; 324M params total, ~103M LM). Architecture: Whisper 128-mel frontend → Qwen3-ASR audio encoder → 4× pre-norm residual MLP tower → adaptive avg-pool (merge factor 4) → LayerNorm + Linear(1024→512) → 8-layer Qwen2-style decoder (hidden 512, tied embeddings, vocab 151936, RoPE 1e6).

Design points:

• Encoder + frontend are 100% reused from qwen3_asr via a small renaming TensorSource (audio_encoder.* ⇄ model.audio_tower.* / model.multi_modal_projector.{linear_1,linear_2}), so the C++ encoder implementation is exercised unchanged; audiocpp_add_model(... DEPENDS qwen3_asr) links it.
• Decoder reuses the shared QwenCausalDecoder with use_qk_norm=false, per-projection Q/K/V attention biases, tied LM head (lm_head = embed_tokens).
• Projector (tower + adaptive pool + projection) is the only new graph code; the adaptive average pool replicates torch.nn.functional.adaptive_avg_pool1d windowing exactly.
• Parity detail: the reference processor emits bfloat16 mel; the audio8 frontend rounds mel to bf16 (RNE) before encoding so fp32 pipelines see the reference values.
• License: checkpoint is CC-BY-NC-4.0. Following the mms_forced_aligner precedent, package_defaults.download is unsupported (local conversion only, no release GGUF redistribution); the safetensors package points at the upstream HF repo and loads directly in the runtime.

Verification

Build (macOS, Apple M4):

cmake -S . -B build/debug -DCMAKE_BUILD_TYPE=Debug -DENGINE_ENABLE_OPENMP=OFF -DGGML_OPENMP=OFF \
    -DAUDIOCPP_MODEL_SET=custom -DAUDIOCPP_MODELS=qwen3_asr,audio8_asr \
    -DENGINE_BUILD_TESTS=ON -DENGINE_BUILD_MODEL_TESTS=ON
cmake --build build/debug --target audiocpp_cli --target audiocpp_gguf -j 8
cmake --build build/debug --target test_audio8_asr_units --target test_audio8_asr_golden_transcription -j 8

Convert + run:

python tools/community_models/convert_audio8_asr.py \
    --checkpoint models/Audio8-ASR-0.1B-hf \
    --converter build/debug/bin/audiocpp_gguf --type q8_0 \
    --output models/Audio8-ASR-0.1B-GGUF/audio8-asr-0.1b-q8_0.gguf

audiocpp_cli --task asr --family audio8_asr \
    --model models/Audio8-ASR-0.1B-GGUF/audio8-asr-0.1b-q8_0.gguf --audio assets/resources/a.wav

Parity evidence (greedy, fp32 HF trust_remote_code reference vs audio.cpp Q8_0 GGUF, exact text match on both backends):

Audio	Reference (fp32)	audio.cpp (Q8_0, Metal)	audio.cpp (Q8_0, CPU)
assets/resources/a.wav (5.95 s)	"This little work was finished in the year eighteen o three, and intended for immediate publication."	identical	—
assets/resources/sample_16k.wav (14.07 s)	"Some call me nature. Others call me Mother Nature. I've been here for over four point five billion years, twenty-two thousand five hundred times longer than you."	identical	identical
61 s clip, fixed 30 s windows	per-window reference transcripts	identical, space-joined	—

The F16 GGUF also matches exactly, and the safetensors package loads directly (no conversion) with the same output.

Tests:

• test_audio8_asr_units — token-count formula (matches reference-observed 1407→176 / 595→74 / 3000→375, clamp-to-1 edge, zero-frame rejection) and bf16 RNE rounding. ctest -R audio8 passes.
• test_audio8_asr_golden_transcription — end-to-end golden transcript via the loader registry; exits 125 (skip) when weights are absent.
• python3 tools/check_loader_catalog_sync.py --self-test and the repo check both pass; audiocpp_cli --list-loaders --json emits audio8_asr with asr: [offline].

Timing: 14.07 s audio transcribed in ~2.7 s wall including model load and session setup (~175% CPU, Metal backend); 61 s in ~6.5 s.

Reference/validation tooling committed: tools/community_models/audio8_asr_reference.py (fp32 reference + golden dumps) and audio8_asr_stages.py (mel / encoder / projector staged tensors).

Model Used

Role	Model
Implementation	Claude Code + GLM5.3-Flash 辅助开发 (assisted development)

Known limitations

• Offline only; no streaming, no word timestamps, no hotword boosting (decode-time logit bias is future work).
• Audio longer than 30 s is transcribed in fixed 30 s windows with space-joined text (no VAD segmentation).
• CC-BY-NC-4.0: local conversion only; GGUF must not be redistributed, so no release GGUF package is advertised by default.

[gqf2008]

Independent review (fresh-context reviewer, APPROVE-WITH-NITS) + fork CI round 1 done. Fix commit f7bc36b addresses the findings:

• Windows CI failure: stray friend class Audio8ASRLoader; made MSVC resolve the name to an incomplete namespace-scope class (clang picked the anonymous-namespace definition) — declaration removed.
• Window sizing now derives from max_audio_samples in the input sample domain (rate-correct at 8/16/24/44.1/48 kHz; sub-16 kHz no longer overflows the encoder position table) with a 0.5 s minimum-tail fold.
• Resident weights file blob is released after weight-store upload (mirrors qwen3_asr; ~halves session RSS).
• Weight storage split: audio_encoder_weight_type limited to native/f32/f16 (qwen3 encoder precedent); malformed option values now fail loudly via the shared runtime parsers; arena knobs declared in the spec.
• Converter rejects sharded safetensors checkpoints (previously silently converted the last shard); same-file sidecar copies skipped.
• tokenizer.json now required (dead legacy branch removed), model_type validated in parse_config, duplicated task/mode guards collapsed, language lists unified, reverse rename map ordered longest-prefix-first.
• WebUI catalog entry removed: GGUF packages are download.kind=unsupported (CC-BY-NC-4.0, local conversion only), so the entry only offered a dead install button (matches the mms_forced_aligner precedent).
• Golden test asserts the raw transcript verbatim; test targets gate on audio8_asr IN_LIST AUDIOCPP_LINKED_MODELS (a76ec04 convention).

Re-verified after the changes: exact-transcript parity on Metal + CPU (a.wav, sample_16k.wav, q8_0 GGUF), 61 s clips at 16 kHz and 8 kHz, unit + golden tests green, check_loader_catalog_sync.py ok. Round-2 fork CI (ci/audio8-asr @ f7bc36b) running.