feat(senpi-codemode): teach eval batching via instruction and reuse-chain examples

[code-yeongyu]

What

Rework the eval tool prompt so batch-through-eval usage surfaces on its own instead of relying on operator steering.

• Instruction: new **Batch through eval.** paragraph — one cell replaces many one-shot tool calls: loop/comprehend over file sets with read()/stdlib, post-process tool.<name>() results programmatically, fan independent calls through parallel(thunks). Absorbs the old "Parallelize work within a cell" sentence (replacement, not addition).
• Examples: the three py reuse-chain slots now demonstrate comprehension+rglob collection → batch read() loop with Counter → parallel() fan-out of tool.grep calls, while keeping the cell-to-cell state-reuse narrative intact. The two rb slots are dropped — rb defaults off, so the default profile never rendered them.
• Dedup: the <critical> sentence duplicated verbatim from the instruction ("Re-run setup only after reset/crash/NameError") is deleted.

Net: prompt teaches harness-specific, non-derivable patterns (thunk shape with d=d binding, tool.<name> args dict, batch-read idiom) in the same slot count; file-mutation and bash payloads intentionally excluded to avoid steering around the edit tool or double-bridging shell.

QA

• npx tsx vitest --run test/ in packages/senpi-codemode: 350 passed / 6 skipped (snapshots updated deliberately, reviewed line-by-line).
• npm run check at repo root: passed (biome, docs, types, neo build+vet+test).
• Prompt-only change to the eval tool description string; no runtime code path touched.

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Summary by cubic

Teaches eval batching in senpi-codemode with a new instruction and Python reuse-chain examples showing batch reads and parallel tool calls. Removes Ruby examples and duplicate guidance; prompt-only change with updated tests.

• New Features
  • Added "Batch through eval." instruction, replacing the old "parallelize within a cell" line.
  • Reworked three Python reuse-chain examples to show: file collection with rglob, batch read() + Counter, and parallel tool.grep fan-out using thunks.
  • Removed Ruby example slots and a duplicated critical sentence about re-running setup.

^{Written for commit 31936d8. Summary will update on new commits.}