tetris-under-contract

Evidence — Neon Tetris, built by an LLM across 5 governed batches

This records the actual run so “coded by Claude Opus 4.8, under a Matrix Builder contract” is verifiable, not asserted.

Environment


Contract engine	`agent-generator` 0.2.0 (the `mb` CLI)
Coder driver	GitPilot (`gitcopilot`) — `gitpilot generate`
LLM provider / model	`claude` / `claude-opus-4-8` (Anthropic Claude Opus 4.8)
Endpoint	`https://api.anthropic.com/v1/messages` (`anthropic-version: 2023-06-01`)

The 5 batches

Each batch ran: mb next → mb prompt --coder gitpilot → gitpilot generate (Opus 4.8, given the contract + the current file + the batch spec) → mb check. The allow-list for every batch was frontend/index.html only; the model never wrote outside it.

#	Batch	Result file	`mb check`	Matrix Commit
1	Foundation (board, 7 pieces, render loop, gravity, lock)	11,025 B	approved · 100	`mc-e5da1ec40b74`
2	Controls + SRS rotation + wall kicks + lock delay + DAS	20,599 B	approved · 100	`mc-ed8f08a81d49`
3	Line clears, scoring, levels, next preview, hold	28,402 B	approved · 100	`mc-1e2903a575aa`
4	Ghost, particles/flash, WebAudio SFX, mobile touch, responsive	44,472 B	approved · 100	`mc-11c9835f1a93`
5	Start/pause/game-over, high score (localStorage), a11y, credit	56,449 B	approved · 100	`mc-c186f714b6a1`

$ mb timeline
Tetris Under Contract  v1.0.0
  Batch 01  Foundation                              ✓ commit 001 mc-e5da1ec40b74
  Batch 02  Controls and SRS rotation               ✓ commit 002 mc-ed8f08a81d49
  Batch 03  Line clears, scoring, levels, next/hold  ✓ commit 003 mc-1e2903a575aa
  Batch 04  Juice: ghost, particles, sound, mobile   ✓ commit 004 mc-11c9835f1a93
  Batch 05  Game states, high score, accessibility   ✓ commit 005 mc-c186f714b6a1

A representative batch (Batch 4)

$ export GITPILOT_PROVIDER=claude GITPILOT_CLAUDE_MODEL=claude-opus-4-8
$ export ANTHROPIC_API_KEY=sk-ant-…          # redacted, temporary, rotated after
$ mb next "Juice: ghost, particles, sound, mobile, responsive"
$ mb prompt --coder gitpilot
$ gitpilot generate -m "$(cat coder-prompts/gitpilot.md) + current file + batch spec" -o .
Provider: claude · Model: claude-opus-4-8
  Created: frontend/index.html (44454 bytes)
$ mb check frontend/index.html
MATRIX_STATUS: approved  score=100
  committed mc-11c9835f1a93

Independent sanity checks

After every batch, the extracted <script> passed node --check (valid JavaScript) and the file ended with a complete </html>.
Final feature scan confirmed: SRS rotation + wall kicks, ghost piece, 7-bag, next/hold, scoring/levels, particles, AudioContext SFX, localStorage high score, touch handlers, and prefers-reduced-motion handling are all present.

Tooling note (honest)

GitPilot’s Anthropic provider didn’t set an explicit max_tokens, so litellm’s low default truncated large single-file generations. I added a configurable max_tokens (GITPILOT_MAX_TOKENS, default 32000) to gitpilot/llm_provider.py so a full game fits in one response. That’s a genuine upstream improvement, not a workaround in the game itself.

The Anthropic API key used was temporary and has been rotated.

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