The universal PARALLEL_TOOL_CALL_GUIDANCE block already lives on main, but it
shipped with two rough edges this change cleans up:
- It duplicated the batching steer for Google models. The
GOOGLE_MODEL_OPERATIONAL_GUIDANCE block still carried its own
"Parallel tool calls" bullet, so Gemini/Gemma received the instruction
twice in one prompt. Drop the redundant bullet — the universal block is now
the single source.
- Its comment claimed "nothing in the open-source system prompt encouraged
batching," which was wrong: the steer existed for Google models only. Reword
to say the gap was that every *other* model got nothing.
- Tighten the test that asserts the steer (precedence-correct), and add an
invariant guarding against re-introducing the Google duplicate.
07e785d60a