feat: Zed edit-predictions keyless FIM route (Qwen2.5-Coder-1.5B / coder-fast)

Deep-research-picked Qwen2.5-Coder-1.5B (BASE, Apache-2.0, native FIM) as a
low-latency inline-completion seat:
- stacks/vllm: vllm-coder service (ana-ml2 GPU1 :8020) + granite shrunk
  (util 0.27->0.13, max-len 131072->16384, seqs 1024->256; granite phasing out)
  to free GPU1 room.
- stacks/litellm: coder-fast alias -> :8020 (mode: completion, /v1/completions).
- stacks/zed-fim-proxy (NEW): keyless /v1/completions front door on ana-docker
  :4141 for Zed (which can't send an auth header) — POST + path + model
  allowlist, injects a coder-fast-scoped virtual key -> LiteLLM :4000. Anon
  /ping liveness. Verified keyless FIM end-to-end.

Zed api_url = http://10.250.50.70:4141/v1, model coder-fast, prompt_format qwen.
Source-IP allowlist off pending the Mac's observed source IP.

stacks/vllm/.env.example

@@ -98,7 +98,10 @@ GRANITE_SERVED_NAME=granite-4.1-8b
 # short parallel calls, so the 64K cap is ample.
 # 131072 — RESTORED 2026-07-16 (native max) for full-chapter summarization; GPU-1
 # freed by the image-bench evict + qwen36-vl gone, so the 128K ctx fits again.
-GRANITE_MAX_MODEL_LEN=131072
+# 16384 — SHRUNK 2026-07-27 (operator: granite is being phased out) to free GPU-1
+# room for vllm-coder (the Zed FIM seat). Full-chapter ctx dropped; util 0.13 holds
+# 16K cleanly (32768 @ util 0.12 crash-looped: KV est-max was only 19376 tokens).
+GRANITE_MAX_MODEL_LEN=16384
 # FP8 KV cache (native on Blackwell cc 12.0). At 50K ≈ ~4.2 GB (vs ~8.4 GB at fp16).
 GRANITE_KV_CACHE_DTYPE=fp8
 # util 0.35 (~33.6 GB) — tuned 2026-06-13 to leave ~3.5 GB free on GPU 1 alongside
@@ -118,8 +121,24 @@ GRANITE_KV_CACHE_DTYPE=fp8
 # 0.27 — RE-GROWN 2026-07-16 (same session) after char-rp moved onto GPU-1: spend the
 # leftover room on full-chapter context (max-len 131072). KV 15.0 GiB = 196,560 tokens
 # = 1.50x @ 131072; GPU-1 lands ~6.7 GB headroom (char-rp 30 + granite 27 + selene 17 + trio).
-GRANITE_GPU_MEM_UTIL=0.27
-# Concurrency cap — set VERY HIGH 2026-07-16 (was vLLM default 128) so the KV pool is
-# the only bound. granite is the fleet fan-out summarizer/classifier (many concurrent
-# SHORT calls); default 128 capped below the KV bound (~192 @ 1K-tok). VRAM-neutral.
-GRANITE_MAX_NUM_SEQS=1024
+# 0.13 — SHRUNK 2026-07-27 (was 0.27) with the max-len drop; frees ~14 GB on GPU-1 for
+# vllm-coder. granite phasing out, so no longer worth the big KV pool. (0.12 was too
+# small for even 16K KV; 0.13 gives ~1.4x @ 16384.)
+GRANITE_GPU_MEM_UTIL=0.13
+# Concurrency cap. Was 1024 (fan-out summarizer); DROPPED to 256 on 2026-07-27 with the
+# phasing-out shrink (256 is ample for the reduced summarizer load; smaller sched state).
+GRANITE_MAX_NUM_SEQS=256
+
+# Qwen2.5-Coder-1.5B (BASE) — FIM code-completion seat for Zed editor inline
+# edit-predictions (deep-research pick 2026-07-27, Apache-2.0). GPU-1, alongside the
+# small-model trio + (phasing-out) granite. Reached via LiteLLM `coder-fast` alias
+# and the keyless zed-fim-proxy (stacks/zed-fim-proxy). util 0.06 (~5.7 GB) holds
+# the 1.5B fp16 + fp8 KV; 8192 ctx is ample for FIM (KV = 13.75x concurrency).
+CODER_PORT=8020
+CODER_GPU_ID=1
+CODER_MODEL=Qwen/Qwen2.5-Coder-1.5B
+CODER_SERVED_NAME=qwen2.5-coder-1.5b
+CODER_MAX_MODEL_LEN=8192
+CODER_KV_CACHE_DTYPE=fp8
+CODER_GPU_MEM_UTIL=0.06
+CODER_MAX_NUM_SEQS=32