feat: round-2 bakeoff — 26b silent-stop is tool-response context size

Round 2 tested the hypothesis that 26B's silent-stop was about
write_file argument size. Result: refuted.

- Patch-mode (apply_patch instead of write_file): 26B fails identically
  at iter 6. Tool-arg size is not the cause.
- Truncation sweep on tool responses reveals the real trigger: cap at
  800 or 1200 chars → 26B PASSES (1200-cap is 8.4s, fastest of any run).
  Cap at 1600, 2000, or unlimited → 26B silent-stops with eval=4.

Revised understanding: 26B silent-stops when cumulative tool-response
context crosses a shape threshold around 1200-1600 chars per response.
Not a tool-arg bug, not a raw code-gen bug — 26B emits correct code
fine in both one-shot and short-context settings.

Production CLI agents (openclaw, open code, aider) typically truncate
tool responses by default, so this failure may not surface in them.
Custom harnesses should cap ≤1200 chars per tool response when
targeting the 26B MoE.

Updates GOTCHAS (rewritten entry with the truncation sweep table),
SYNTHESIS model-selection row, CORPUS_cli_coding_agent.md pointer,
docs/reference/bakeoff-2026-04-18.md with full Round 2 methodology
and data.

Adds harness_patch.py (apply_patch edit tool), harness_patch_truncated.py
(env-configurable TOOL_RESULT_CAP), all 7 run logs, and a
.secrets.baseline for detect-secrets false positives on JSON timestamps.

CORPUS_cli_coding_agent.md

@@ -6,13 +6,16 @@
 > `IMPLEMENTATIONS.md` chat-agent patterns (Simon) and pipeline patterns
 > (AI_Visualizer).
 
-> **Empirical follow-up:** `docs/reference/bakeoff-2026-04-18.md` — real runs of
-> `gemma4:26b`, `gemma4:31b-it-q4_K_M`, and `qwen3-coder:30b` against a custom
-> minimal CLI-agent harness on a fix-the-median-bug task. Key findings:
-> **31B clean (8 iters, 1 write), Qwen3-Coder correct but chatty (15 iters),
-> 26B reproducibly silent-stops at the `write_file` tool call boundary** even
-> though it can produce the fix in a direct one-shot call. Read when: scoping
-> which model to point an agent at, or hitting an unexpected tool-call halt.
+> **Empirical follow-up:** `docs/reference/bakeoff-2026-04-18.md` — 2 rounds of
+> runs against a custom minimal CLI-agent harness on a fix-the-median-bug task.
+> **Round 1:** 31B clean (8 iters), Qwen3-Coder correct but chatty (15 iters),
+> 26B silently quits with zero edits. **Round 2 (diagnostic):** the 26B failure
+> is NOT about edit-tool-argument size — it's about **cumulative tool-response
+> context shape**. Capping tool responses ≤1200 chars makes 26B pass cleanly
+> *and* in the fastest wall time of any run (8.4s). Most production CLI agents
+> already truncate tool responses, so the issue may be invisible in them.
+> Read when: scoping which model to point an agent at, hitting an unexpected
+> tool-call halt, or writing a custom harness targeting the 26B MoE.
 
 ## TL;DR