fix: walk back round-1/2 conclusions — the cause was think=false all along

Seth asked "was this with think=false?" Yes — and that was the only
question that mattered. Everything I concluded in round 1 and round 2
was wrong.

Actual cause, isolated in round 3:
- At identical message state, gemma4:26b with think=false returns
  eval=4 (silent stop); with think unset or think=true, returns
  eval=165 and emits the correct tool call.
- Original round-1 write_file harness + think unset: 26B passes in
  8 iters, 20s. No mitigations needed.
- 31B dense and qwen3-coder:30b tolerate think=false; 26B MoE does not.

Red herrings (kept on-record in the bakeoff doc, not silently erased):
- Round 1: "write_file tool-call argument size" — wrong
- Round 2a: refuted the arg-size theory but for the wrong reason
  (still failed because think=false was still set)
- Round 2b: "cumulative tool-response context size" — truncating
  did make 26B pass, but by coincidence. Shorter context at the
  decision turn dodged the think=false side effect.

Why the existing "always think:false" guidance was misleading:
it was derived from AI_Visualizer (single-turn JSON pipelines) where
thinking tokens do eat num_predict invisibly. In multi-turn
tool-calling agents the channels are separate and the flag has a
different effect — catastrophic on 26B specifically.

Doc updates:
- GOTCHAS: replaced the 26B entry with the actual cause; scoped the
  original "Thinking Mode Eats Context" entry to single-turn pipelines
- SYNTHESIS: split the "Mandatory Ollama Settings" block into
  single-turn vs multi-turn variants; updated anti-patterns and
  quick-start checklist
- CORPUS_cli_coding_agent.md: revised pointer and config template
- docs/reference/bakeoff-2026-04-18.md: added Round 3 section with
  the correction notice at the top of the file and full diagnostic
  methodology

New artifacts: harness_no_think_flag.py, harness_write_no_think.py,
and 4 new log files demonstrating all three models pass when think
is left at default.

.secrets.baseline

@@ -141,6 +141,15 @@
         "line_number": 5
       }
     ],
+    "scripts/bakeoff/runs_patch/qwen3-coder-30b-no-think-flag/log.json": [
+      {
+        "type": "Base64 High Entropy String",
+        "filename": "scripts/bakeoff/runs_patch/qwen3-coder-30b-no-think-flag/log.json",
+        "hashed_secret": "a5781a432dbf3d4f4abf095833e368838fa0d098",
+        "is_verified": false,
+        "line_number": 5
+      }
+    ],
     "tooling/fine-tuning/google-cookbook/Gemma_4_HDP_Agentic_Security.ipynb": [
       {
         "type": "Hex High Entropy String",
@@ -14570,5 +14579,5 @@
       }
     ]
   },
-  "generated_at": "2026-04-18T17:40:02Z"
+  "generated_at": "2026-04-18T22:14:05Z"
 }