feat(selene): retire the seat; chat-judge -> gen, selene-1-mini-8b 404s by design

Benchmarked selene against gen on selene's own job: 24 designed judge items
with checkable ground truth, pairwise + absolute modes, 3 repeats, on BOTH a
neutral JSON prompt and Selene's native Atla template. 288 calls, all free
local.

  neutral JSON     selene 20/24 (83%)   gen 23/24 (96%)
  native Atla      selene 21/24 (88%)   gen 22/24 (92%)

gen won on both templates and selene's BEST sat below gen's WORST. Selene was
given its own fine-tuned template as a fairness check; it gained one point,
not the three it needed.

Decisive defect: selene cannot emit "tie" -- 0/2 on both templates, forcing a
winner on every equivalent pair. For eval work that is the case that matters
most. gen returned tie correctly on the JSON template. Selene also compressed
the 1-5 scale (clustered at 2s and 4s) where gen used it fully. Selene's only
win was ~3x latency, unexercised at ~60 calls/day with zero queueing.

TWO NAMES, TWO DIFFERENT TREATMENTS, deliberately:

- chat-judge -> repointed to gen. It is a ROLE alias and ADR-0012 says
  consumers bind the capability, not a concrete model. Sampler profile copied
  from image-judge (temp 0, top_p 1.0, top_k 1, thinking off) so the served
  config matches the benchmarked condition.

- selene-1-mini-8b -> REMOVED. It 404s. It was NOT aliased to gen. A
  served-name is a contract about what the model IS; answering it with a
  different model hides a material change behind a stable string. Operator
  ruling: "never repoint a named model at a different model's endpoint --
  that is intentionally misleading." Verified: the gateway now returns
  HTTP 400 "Invalid model name" for it.

Reclaimed 17.2 GiB on ana-ml2 GPU 1 (free 1,818 -> 19,450 MiB) on a card that
had under 2 GiB of headroom. gen already runs on GPU 0, so the judge role
moved onto an existing seat rather than allocating anything new.

Canonical litellm config synced from the host; ana-ml2 README and
recommended-model-settings updated. compose.yaml kept for reference, not
deployed.

stacks/litellm/conf/config.yaml

@@ -337,19 +337,24 @@ model_list:
     model_info:
       mode: chat
 
-  # --- Selene 1 Mini 8B (AtlaAI judge, FP8) — restored on GPU1 after the
-  #     llama-swap teardown (was the Q6_K GGUF in the swap zoo). vLLM dynamic fp8,
-  #     :8011. Explicit entry shadows the "*" wildcard (which used to reach it via
-  #     llama-swap). Hallucination/RAG-faithfulness judge; callers set temp ~0.01. ---
-  - model_name: selene-1-mini-8b
-    litellm_params:
-      model: hosted_vllm/selene-1-mini-8b
-      api_base: http://10.250.50.54:8011/v1
-      api_key: os.environ/VLLM_API_KEY
-      temperature: 0.6
-      top_p: 0.9
-    model_info:
-      mode: chat
+  # --- selene-1-mini-8b RETIRED 2026-08-23. AtlaAI Selene 1 Mini (Llama 3.1 8B,
+  #     dynamic FP8) on ana-ml2 GPU1 :8011. Benchmarked head-to-head against `gen`
+  #     on its OWN job: 24 designed judge items with checkable ground truth,
+  #     pairwise + absolute scoring, 3 repeats, run on BOTH a neutral JSON prompt
+  #     and Selene's native Atla template (288 calls total). gen won on both —
+  #     23/24 vs 20/24 neutral, 22/24 vs 21/24 native. Selene's BEST score sat
+  #     below gen's WORST. Decisive defect: it cannot emit "tie", forcing a winner
+  #     on every equivalent pair (0/2 on both templates), which is fatal for eval
+  #     work where close pairs are the whole point. Seat downed to reclaim 17.2 GiB
+  #     on GPU1 (the card had 1.8 GiB free). Its only edge was ~3x lower latency,
+  #     unexercised at its observed ~60 calls/day with zero queueing.
+  #
+  #     DELIBERATELY NOT ALIASED TO ANOTHER MODEL. A caller asking for
+  #     `selene-1-mini-8b` must never silently receive qwen3.8-27b — a served-name
+  #     is a contract about what the model IS, and a silent substitution hides a
+  #     material change behind a stable string. This name now 404s BY DESIGN.
+  #     Repoint consumers to `chat-judge` (the role alias, below) or to `gen`
+  #     explicitly. Operator ruling 2026-08-23. ---
 
   # --- Qwen3 embeddings ---
   - model_name: qwen3-embedding
@@ -374,14 +379,26 @@ model_list:
   #     model; swap the backing model here and callers are unaffected. NO generic
   #     `embedding` alias ON PURPOSE — embedding vectors are model-specific (not
   #     swap-transparent), so that capability stays `qwen3-embedding` above. ---
-  # chat-judge → generative LLM-as-judge (Selene); WT selene-judgment role.
+  # chat-judge → generative LLM-as-judge; WT selene-judgment role. Backed by
+  #   Selene until 2026-08-23, now `gen` / qwen3.8-27b-uncensored (:8015) after
+  #   Selene lost the head-to-head on its own job and its seat was reclaimed.
+  #   This is precisely the ADR-0012 case stated above: the ROLE alias moves, the
+  #   MODEL NAME does not — which is why selene-1-mini-8b was retired outright
+  #   rather than repointed. Sampler profile copied from image-judge
+  #   (deterministic, thinking off); the benchmark that selected gen ran at
+  #   temperature 0, so this matches the tested condition.
   - model_name: chat-judge
     litellm_params:
-      model: hosted_vllm/selene-1-mini-8b
-      api_base: http://10.250.50.54:8011/v1
+      model: hosted_vllm/qwen3.8-27b-uncensored
+      api_base: http://10.250.50.54:8015/v1
       api_key: os.environ/VLLM_API_KEY
-      temperature: 0.6
-      top_p: 0.9
+      temperature: 0
+      top_p: 1.0
+      extra_body:
+        top_k: 1
+        repetition_penalty: 1.05
+        chat_template_kwargs:
+          enable_thinking: false
     model_info:
       mode: chat
   # reranker → generic capability name for rerank (currently qwen3-reranker).