memory: chatterbox-fast tail-degradation diagnosed + fixed (max_chunk_chars=250 cap)

Long operator-driven diagnosis: the 'broken/German/dead-air' was the Turbo T3
model over-running its generation tail (garble in final ~2-3s, worse with
length + tight sampling), NOT a language leak or OOM. Fix = server-side
max_chunk_chars=250 cap (:v2), keeping 3-4 sentence clean chunks with smooth
joins. Method (amplitude-gated voiced-ZCR), foot-guns (tail-trim unreliable,
build-context/image drift), and the flat-vs-repo divergence recorded.

persistent-memory.md

@@ -130,6 +130,8 @@ _As of 2026-08-07 — heavy overnight session landed; b182 deployed and the oper
 
 ## Recent decisions
 
+- `[2026-08-07]` **chatterbox-fast "broken audio" root-caused (T3 AR tail over-run) + FIXED (max_chunk_chars=250 cap, :v2 deployed).** Long saga, operator-driven clean diagnosis. **Symptom:** ratatoskr's migrated RP-surface TTS "swaps to German" / "dead air" / "garbage" on long turns. **NOT** German-leak (Turbo `generate()` has NO language param — plain AutoTokenizer, no `language_id`; the multilingual `language_id="en"` lever lives only in the separate `ChatterboxMultilingualTTS`), **NOT** OOM alone. **Real cause:** the Chatterbox **Turbo T3 model OVER-RUNS its generation tail** — a long single `generate()` degrades into garble/dead-air in its final ~2-3s (lib filters OOV tokens `<6561` + pads silence = messy AR tail). The scheduler's buffer-ratchet builds 300-600 char mega-chunks that land in that zone; streaming concatenates each bad tail (worst case). **ratatoskr's anti-"German" knobs (top_k=80/temp=0.5) made it WORSE** — tight sampling pulls the degradation onset SHORTER (~200 chars vs ~300 at default knobs). **Diagnosis method** (deterministic, no ears-only): single-shot length sweep + **amplitude-gated voiced-ZCR** (garble spikes ZCR; must gate on |x|>500 else trailing silence confounds it) — degraded voiced-tail = 1.58× mid, clean = ~0.64-1.1×. **FIX:** server-side `max_chunk_chars=250` cap on the scheduler (`:v2` image, `CBF_MAX_CHUNK_CHARS=250` env) — bounds each generation to just under the ~300-char onset → clean **3-4 sentence** chunks (max prosodic arc while clean). Operator ear-confirmed clean audio + clean joins; **chatterbox's low emotiveness keeps chunk joins smooth** (the harsh joins that got Zonos rejected are absent — operator's key call). **ratatoskr TODO (relayed msg `01KZER9X7S`):** revert knobs to default (top_k→1000, temp→0.8), send full text (server chunks internally), keep the 503-on-empty guard. **Cap value tunable** per-request (`max_chunk_chars`) + env. **Deeper prosody** (if ever wanted) = scheduler Phase-2 context-priming at joins (feed prior sentence as discarded-audio context; +latency). **⚠ FOOT-GUNS:** (1) acoustic tail-trim is UNRELIABLE — sibilants ('s'/'sh'/'f') spike ZCR like garble, can't cleanly detect the speech→garble boundary. (2) **build-context vs image drift** — the `:v2` image was built from cap source, but after a `:v1` rollback the build context held `:v1` source → a `docker compose build` would've silently produced a cap-less `:v2`; re-synced the flat cap source to `/opt/docker/compose/chatterbox-fast/` (rebuild-verified). **⚠ DIVERGENCE (follow-up):** deployed build context is FLAT (`app.py`/`scheduler.py`, `from scheduler import`, thin-overlay `FROM local/chatterbox:v1`, cap-only) vs the `vh/chatterbox-fast` REPO which is PACKAGE-layout (`chatterbox_fast/`, `from chatterbox_fast.scheduler`, self-contained Dockerfile) + has `norm_loudness` (repo commit `6bc7bf0` = cap; deployed omits norm_loudness deliberately to keep the ear-test unconfounded). Reconcile the two layouts so a repo-based rebuild matches deploy. Rollback: `.bak-cap-20260807-104850` backups on irv-ml1 + `:v1` image both retained. [[reference_chatterbox_fast_repo]] [[reference_zonos_tts_stack]]
+
 - `[2026-08-07]` **Zonos2 TAKEN DOWN on the 3090 (irv-ml1) — operator-directed "for memory", TEMPORARY.** Freed ~17.4 GB (3090: 728 MiB → 18.2 GB free) so chatterbox-fast (co-resident, was OOMing on long generations) has headroom. **⚠ Restore is manual — Zonos2 :1920 was a DETACHED native process (NOT systemd/docker), reparented to init.** GPU memory was held by the `--multiprocessing-fork` CHILDREN (1966165=16.4G, 1966166=1G), which ORPHAN to init when you kill the parent — had to SIGTERM the children explicitly (killing the parent 1965942 + uv-run 1965935 alone left the 16.4G held). **RESTORE CMD** (from irv-ml1, user lkraven): `cd /home/lkraven/tts-audition/models/zonos2 && nohup uv run python -m zonos2 --model-path Zyphra/ZONOS2 --host 0.0.0.0 --port 1920 --tts-default-voices-dir ./default_voices/ --cuda-graph-max-bs 1 --num-pages 16384 --max-running-requests 2 --memory-ratio 0.3 > /tmp/zonos2.log 2>&1 &` then `docker start zonos-gateway`. **Consumers that lost Zonos:** asset-engine + gateway-chat (via LiteLLM `ext-tts` alias → zonos-gateway :8890, now stopped); ratatoskr already migrated OFF to chatterbox-fast (unaffected). Also unblocks proper drift/cap testing (OOM was blocking it). [[reference_zonos_tts_stack]]
 
 - `[2026-08-07]` **chatterbox-fast: donut voice added + full contract delivered to ratatoskr-dev (their TTS migration off Zonos).** Operator-directed. Copied `zonos-gateway/voices/Donut.wav` → chatterbox `/refs` (`/worktank/chatterbox/reference_audio/donut.wav` — the reference_audio SUBDIR is lkraven-owned so no sudo despite `/worktank` root; container globs `/refs` live → **NO restart**), exposed as `voice:"donut"` (lowercase); verified clean 7.5s synth (24kHz, RTF ~0.31). A/B booth (chatterbox vs zonos donut, same line) at `http://10.100.10.50:8090/b/donut-chatterbox/`. Answered ratatoskr's 8-question contract ask from the live gateway (`local/chatterbox-fast:v1`) + source: **NOT OpenAI-shaped** (`POST /tts`; body `text`/`voice`/`format`/`stream`, not `input`/`model`/`response_format`); **NO affect dials** (Turbo ignores cfg_weight/min_p/exaggeration — the architecture-changing answer they flagged; **Zonos stays the only fleet TTS with real emotion steering**); streaming WAV placeholder-header shape IDENTICAL to Zonos (their per-chunk Web Audio path survives); SR 24000 (Zonos 44100); server chunks arbitrary-length text internally (no client-side chunking, unlike Zonos's 71.2s cap); English-only, no language pin. **FYI-worthy (operator):** ratatoskr is moving its RP-surface TTS OFF Zonos back to chatterbox-fast → loses the live-PAD affect coupling (heavy Zonos emotion investment) — their call, trade-off flagged to them. auto-memory `reference_chatterbox_fast_repo` enriched w/ the live contract. [[reference_zonos_tts_stack]]