Swap the MeroMero A4B onto the erp-seat seat as char-rp-fast, retire the Pfish-6 alias

Operator: "replace that a4b moe over pfish-6 -- remove the pfish-6 alias and
create an alias for char-rp-fast."

G4-MeroMero-26B-A4B-it-uncensored-heretic-NVFP4A16 is live on ana-ml2 :8021 under
its own served name, behind the new gateway alias char-rp-fast. Pfish-6 is gone
from the gateway and now returns an explicit 400 rather than a substitution; 0 of
17 LiteLLM keys scoped it, so nothing was orphaned. The compose project name stays
erp-seat because asset-engine derives seat liveness from it.

The first quant of that A4B served NaN and passed its healthcheck doing it. It was
built with the dense v2-31B recipe, whose ignore list has no router regex, so all
30 MoE routers were quantized to 4 bits -- and a 4-bit router changes which experts
run rather than degrading them. Quant rc=0, healthcheck green, correct KV pool,
correct served name, and every completion returned finish_reason=length with the
full token count and content: null. The model was emitting a full budget of tokens
that decoded to the empty string. Raw /v1/completions was empty too, ruling out the
chat template and the reasoning parser. The signal that named it was logprobs:
vLLM refused to serialize the response, "Out of range float values are not JSON
compliant: nan".

The lesson is about the control rather than the router. That tree had already been
structurally diffed and passed -- against a verified-good DENSE quant of the same
Gemma-4 family. A dense model has no routers, so the single thing that was wrong
was the single thing the control could not distinguish. Diffing instead against
Pfish-6, a known-good quant of the same 26B-A4B MoE, gave it in one line: 222
ignore entries against 252, the 30 missing being layers.N.router.proj. A positive
control is only worth what it can distinguish, and "same family" is not "same
architecture class".

Re-quantized with the MoE recipe, whose dry-run asserts 11,520 expert Linears and
refuses a router in the quantize set before any GPU time. The live seat then passed
prose with no channel-prefix leak, a solid-colour image read correctly, an auto
tool call parsed, finite logprobs, and KV 534,649 tokens / 2.04x carried over from
Pfish-6 unchanged. The broken tree is parked on ana-ml2 as
...-NVFP4A16.BROKEN-routers-quantized-20260910.

Section 4.4's temp port was not reachable: 15.9 GiB of weights plus KV plus
multimodal encoder-cache profiling does not fit in the ~19 GiB free beside GPU1's
six other tenants -- 0.20 utilization refused admission, 0.185 OOM'd in encoder
profiling. The substitute was reversibility and ordering: named .env backup, prove
the seat on its real port while no alias points at it, move the alias last. That is
why a NaN-serving seat never reached a consumer. The seat was down about 16 minutes
across two attempts; no consumer saw a broken alias.

Playbook gains the router-quant failure signature and the control-class rule in
3.15, and a logprobs check in 4.4. seat_verify.py carries that check as check 6.

Quality is NOT established: no RP eval, no long-context check, no A/B against
Pfish-6 or char-rp. Samplers are the author's card values, untuned here.

persistent-memory.d/2026-09-10-meromero-quants-and-the-pinned-transformers-trap.md

@@ -119,4 +119,45 @@ GPU1 beside the current tenants regardless.
 Instruments and the full write-up: `services/meromero-quant/`. General lessons:
 `docs/pfi/model-quantization-playbook.md` §3.16, **§3.17 (new)**, §4.3.
 
+
+## The A4B reached a live seat while broken — and looked healthy doing it
+
+Operator, later the same day: *"replace that a4b moe over pfish-6 — remove the pfish-6 alias and
+create an alias for char-rp-fast."* The A4B went onto the `erp-seat` seat (ana-ml2 `:8021`) and
+**served NaN**.
+
+Cause: the morning's batch used the **dense** recipe for a **MoE** model. Its IGNORE list has no
+`re:.*router.*`, so all 30 MoE routers were quantized to NVFP4, and a 4-bit router does not degrade
+expert selection — it changes which experts run.
+
+**Nothing in the normal startup path showed it.** Quant `rc=0`. Healthcheck green in 210 s. Engine
+log reported the correct KV pool. `/v1/models` correct. Every completion came back
+`finish_reason=length` with the **full** token count and `content: null` — the model was generating
+a full budget of tokens that decoded to the empty string. Raw `/v1/completions` was empty too, which
+ruled out the chat template and the reasoning parser. The one signal that named it: `logprobs: 1`
+→ HTTP 400 `Out of range float values are not JSON compliant: nan`.
+
+⚠⚠ **The durable lesson is about the CONTROL, not the router.** That broken tree HAD been
+structurally diffed before it shipped — and passed — against a verified-good **dense** 31B quant of
+the same Gemma-4 family. A dense model has no routers, so the single thing that was wrong was the
+single thing that control could not distinguish. **A positive control is only worth what it can
+distinguish; "same family" is not "same architecture class."** Diffing instead against **Pfish-6**
+— a known-good NVFP4A16 quant of the same 26B-A4B MoE — gave the answer in one line: 222 ignore
+entries against 252, the 30 missing being exactly `model.language_model.layers.N.router.proj`.
+
+Re-quantized with `services/erp-seat-quant/quant_nvfp4a16_gemma4_moe.py`, whose `--dry-run` asserts
+11,520 expert Linears and refuses a router in the quantize set, both before any GPU time. 90 s.
+Live seat then passed prose / vision / tool-call / logprobs. Broken tree parked as
+`...-NVFP4A16.BROKEN-routers-quantized-20260910`.
+
+**§4.4's temp port was not reachable, and the fallback mattered.** 15.9 GiB of weights + KV +
+multimodal encoder-cache profiling does not fit in ~19 GiB free beside GPU1's six other tenants:
+`gpu-memory-utilization 0.20` refused admission (18.26 free vs 18.99 wanted) and `0.185` OOM'd in
+encoder profiling. Substitute: named `.env` backup, prove the seat on its real port **while no
+gateway alias points at it**, move the alias last. That ordering is the only reason a NaN-serving
+seat never reached a consumer. Cost: ~16 min of seat downtime, twice; zero broken aliases.
+
+Runbook: `services/erp-seat-quant/RUNBOOK-char-rp-fast-swap.md`. Playbook §3.15 (failure signature +
+the control-class rule), §4.4 (ask for logprobs once).
+
 Related: [[2026-09-10-r49-babybronte-d1-d3-and-the-1-epoch-pilot]]