feat(erp-tune): run 7 launched on pfi-gx10 (opening-split slot + mask union) — config, launcher, builder, runbook; erp-seat: pin vLLM nightly 311b3513 (forced tool_choice 1/9 -> 6/9, round trip clean), README on the gemma4-parser design limit

stacks/erp-seat/README.md

@@ -19,6 +19,18 @@ checkpoint so the GX10 is free to train the next run. First occupant: **run 6**
   the model answers in prose (3/3). The rest of the matrix (auto / required / named / parallel /
   nested schema / empty `tools: []` / streaming / tool-result round trip) was green before and
   after. `stacks/gemma4-charrp` has the same exposure and does NOT carry the flag yet.
+- **Forced tool_choice (named / `required`) is prompt-driven on EVERY Gemma-4 seat, not
+  grammar-enforced — by vLLM design.** `vllm/tool_parsers/gemma4_engine_tool_parser.py` sets
+  `supports_required_and_named = False` and its `adjust_request` deliberately skips the
+  structured-output JSON for required/named so the model can emit its native
+  `<|tool_call>call:…` syntax. A tune that weakened that syntax (this ERP tune) therefore
+  honours forced calls only sometimes. Measured 2026-09-08, 3 conversations × 3 turns, real
+  system prompt: v0.26.0 **1/9**; nightly `311b3513` (v0.27.2rc1, the `gen` seat's image) **6/9**
+  and the tool-result round trip stays clean 3/3 — so the seat runs the nightly. tts-dev measured
+  0/18 on v0.26.0 with `gen` 18/18 as the positive control, and **`response_format:
+  json_schema` (guided decoding) 18/18 on this seat** — that is the deterministic path for a
+  forced call; `tool_choice: auto` works normally. A parser plugin that re-enables guided JSON
+  would also need JSON extraction in the engine-parser path; not attempted.
 - **GPU1 is shared** — check real usage (`nvidia-smi --query-compute-apps=pid,used_memory`) before
   raising `ERP_GPU_MEM_UTIL`; the flag sizes KV, not CUDA context.
 - **Rollback / next run:** point `ERP_MODEL` + `ERP_SERVED_NAME` at the next quant dir, keep the