feat: CLI coding agent bakeoff — 26b reproducibly silent-stops at write_file

Ran minimal agent loop (Ollama /api/chat + read_file/write_file/run_bash) on
steel141 3090 Ti against 3 models on a broken-median-function task:

- gemma4:31b-it-q4_K_M: PASS (8 iters, 1 write, 44s) — textbook trace
- qwen3-coder:30b: PASS (15 iters, 1 write, 22s) — correct but chatty
- gemma4:26b: FAIL (6 iters, 0 writes) — silently stops with eval=4
  after reading source. Reproduced on second run. One-shot probe
  confirms 26b CAN produce the correct fix — failure is specifically
  at the write_file tool-call argument boundary.

Updates GOTCHAS with a new HIGH-severity entry, SYNTHESIS model-selection
table, CORPUS_cli_coding_agent.md empirical-follow-up pointer, and adds
docs/reference/bakeoff-2026-04-18.md with the full writeup.

README.md

@@ -15,6 +15,7 @@ Research corpus and implementation guidance for Google Gemma 4, based on product
 | `CORPUS_benchmarks.md` | Full benchmark table vs Gemma 3, arena scores, agentic scores | When comparing Gemma 4 to alternatives |
 | `CORPUS_tool_calling_format.md` | Native token format + JSON API format for function calling | When implementing tool calling |
 | `CORPUS_cli_coding_agent.md` | Positioning Gemma 4 for CLI coding agent use (openclaw / open code / pi / hermes / aider style). Honest take on what Google did and didn't measure, head-to-head with `qwen3-coder:30b`, homelab setup pointer | When scoping a CLI coding agent or deciding Gemma 4 vs Qwen3-Coder |
+| `docs/reference/bakeoff-2026-04-18.md` | Raw results: CLI-coding-agent bakeoff of gemma4:26b / gemma4:31b / qwen3-coder:30b on steel141 3090 Ti. **31B clean, Qwen3-Coder correct but chatty, 26B reproducibly silent-stops at write_file.** Harness at `scripts/bakeoff/` | When deciding which model to back a CLI agent with, or debugging a similar tool-call halt |
 | `tooling/` | **Canonical upstream tooling** — real scripts, notebooks, model cards, and configs pulled from Google / HF / framework maintainers (147 files). Subdirs: `google-official/`, `huggingface/`, `inference-frameworks/`, `gemma-family/`, `fine-tuning/`. See `tooling/README.md` for index and findings that update the older `CORPUS_*` docs | When you need authoritative source material — model cards, chat templates, fine-tuning recipes, serving commands for vLLM / llama.cpp / MLX, or to scope a specialized sibling (ShieldGemma, EmbeddingGemma, etc.) |
 
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