- Claude Code: 2.1.203 (native, commit b90c3643145a), darwin-arm64
- Auto-update: enabled, channel = latest
- Python: 3.11 (framework install), pytest + pygame versions TBD after venv setup
- Date of run: 8th July 2026
- claude --version: 2.1.203 (Claude Code) # binary can auto-update between sessions
- Model (session banner): <e.g. Opus 4.8>
- Trust prompt: accepted
- CLAUDE.md loaded: verified via <//context / behavioural question>
- If behavioural: asked "what do the project rules say about modifying tests?", answer quoted the rule correctly: <yes/no>
- /agents: loop-referee listed as project agent: <yes/no>
- Permissions posture: per-action approval; settings.json allow-rule for pytest in place
- Repo state at session start: tag/commit , tests/ empty
Custom agents · .claude/agents/
Project
└ loop-referee: 34 tokens
Memory files · /memory
└ CLAUDE.md: 212 tokens
Skills · /skills
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├ verify: ~150 tokens
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├ run: ~120 tokens
├ code-review: ~120 tokens
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└ init: ~20 tokens
Prompt (verbatim):
Read SPEC.md and MILESTONES.md. Write acceptance tests for milestone 1 only, in tests/test_m1_movement.py. Import from snake.engine, which does not exist yet. Do not write any implementation code. Seed all randomness.
Agent behaviour during turn:
All in scope. I'll write M1-only acceptance tests — head advancement, tail vacating (length preserved), body following, direction changes, and reversal-ignored. I'll stay out of M2 (food/growth), M3 (collision), and M4 (determinism), and seed all RNG explicitly.
⏺ Write(tests/test_m1_movement.py) Wrote 98 lines to tests/test_m1_movement.py
… +88 lines
Let me confirm the test file is syntactically valid (it will fail to run since snake.engine doesn't exist yet — that's expected and intended):
Ran 1 shell command
Done. Wrote tests/test_m1_movement.py with M1-only acceptance tests. Syntax compiles clean; the suite fails exactly as expected — ModuleNotFoundError: No module named 'snake.engine' — since no implementation exists yet, which is the point.
What the tests cover (M1: grid and movement):
- Head advances one cell in the stepped direction, in all four directions (respecting y-down: UP decreases y)
- Tail vacates → length preserved when not growing
- Body segments follow the head (each shifts into the predecessor's old cell)
- Perpendicular (90°) turns are honored
- 180° reversal is ignored, snake continues its current direction (both vertical and horizontal cases)
- Multiple steps compound correctly
- Initial score == 0 and game_over is False
Deliberately out of scope (left for their own milestones): food spawning/growth (M2), wall/self collision and the tail-vacate collision rule (M3), and seed-determinism of the food sequence (M4).
All randomness is seeded — every GameState gets random.Random(0) and an explicit food=(0, 0), so nothing depends on unseeded RNG even though M1 movement doesn't trigger a spawn. I only created the new test file; no implementation code was written and no existing files were touched.
✻ Churned for 47s
Prompt (verbatim):
Read SPEC.md and MILESTONES.md. SPEC.md has been amended since you last read it; re-read it in full. Write acceptance tests for milestone 2 only, in tests/test_m2_food.py. Import from snake.engine, which does not exist yet. Do not write any implementation code. Do not test collision or game-over behaviour; that is milestone 3. Seed all randomness.
Agent behaviour during turn:
Read 2 files
SPEC re-read — noting the amendment (the new "Default construction" section, lines 34–37). Writing M2 tests now, covering only food/growth: seeded spawn on a non-body cell, eating increments score and grows the snake, growth via pending_growth, and the no-eat case. Collision/game-over scenarios are deliberately excluded (M3), and I keep every stepped scenario collision-free.
⏺ Write(tests/test_m2_food.py) Wrote 97 lines to tests/test_m2_food.py
… +87 lines
Ran 1 shell command
Done. Wrote tests/test_m2_food.py — syntax compiles, and it fails exactly as expected on ModuleNotFoundError: No module named 'snake.engine' since no implementation exists yet.
What the tests cover (M2: food and growth):
- Eating increments score (head moves onto the food cell)
- Eating grows the snake by one — the tail is withheld on the eating tick
- New food spawns off the body and within grid bounds after eating
- A deterministic "only free cell" case (3×2 grid, snake fills 5 of 6 cells) proving food never spawns on the body, seed-independent
- No-eat tick leaves score and food untouched and vacates the tail normally
- pending_growth withholds the tail one segment per tick then stops (driven via the constructor, no food), and growth alone doesn't score
- Food coordinate is stable across a non-eating tick
Deliberately excluded (per your instruction): all collision and game-over behaviour (M3), and the same-seed-identical-sequence determinism check (M4). Every stepped scenario is kept collision-free — no walls hit, no self-intersection — so nothing here depends on M3 logic.
All randomness is seeded: every GameState gets random.Random(0), and the one grid-full spawn assertion is constructed to have a single free cell so it holds regardless of the seed.
✻ Worked for 1m 34s
Prompt (verbatim):
Read SPEC.md and MILESTONES.md. SPEC.md has been amended since you last read it; re-read it in full. Write acceptance tests for milestone 2 only, in tests/test_m2_food.py. Import from snake.engine, which does not exist yet. Do not write any implementation code. Do not test collision or game-over behaviour; that is milestone 3. Seed all randomness.
Agent behaviour during turn:
Read 2 files
SPEC and MILESTONES re-read (no further changes). M4 is "Determinism and speed hook": same seed ⇒ identical food sequence, and the engine exposes score for the renderer's tick rate. I'll test reproducibility with a deterministic self-driving policy (so any divergence must come from the engine's RNG handling), that the seed actually drives spawns, and that score is an exposed int reflecting foods eaten.
⏺ Write(tests/test_m4_determinism.py) Wrote 117 lines to tests/test_m4_determinism.py
… +107 lines
Ran 1 shell command
Done. Wrote tests/test_m4_determinism.py — compiles clean, fails only on the expected ModuleNotFoundError: No module named 'snake.engine' since no implementation exists yet.
What the tests cover (M4: determinism and speed hook):
- Same seed ⇒ identical initial food and snake at default construction.
- Same seed ⇒ identical food sequence over a full self-played game — a deterministic greedy driver plays both runs, so any divergence would have to originate in the engine's RNG use, not the test. It also asserts the run contains at least one respawn (len(set(foods)) >= 2) so the equality isn't vacuous.
- Explicit scripted lockstep — a second, driver-independent check: two same-seed games given the same hard-coded move list stay identical tick-by-tick (food, snake, score, game_over), including the RNG spawn from an eat.
- Seed actually drives spawning — six different seeds don't all produce the same sequence, catching an engine that ignores its rng.
- score exposed as a plain int starting at 0 and incrementing on an eat — the value the renderer's tick-rate ramp consumes. The ramp logic itself stays in the renderer (M5); the engine remains time-agnostic per SPEC.
All randomness is seeded (random.Random(...) everywhere) and the helper driver is purely deterministic — no unseeded RNG, no reliance on iteration order.
Note: I only added this test file. Per the milestone rules I haven't written any engine code, and M4's tests will stay red until M1–M3 and the engine exist. If you'd like, the natural next step is implementing snake/engine.py so M1→M4 can go green in order.
✻ Cogitated for 1m 56s
Prompt (verbatim):
Implement milestone 1 only... use the loop-referee subagent to verify, and report its output
Agent behaviour during turn:
I'll start by reading the spec and milestones to understand what milestone 1 requires.
Searched for 1 pattern, read 2 files, ran 1 shell command
Let me read the M1 test and the package init to understand the exact API expected.
Read 3 files
Now I understand M1. Let me implement snake/engine.py for milestone 1 (grid, movement, reversal-ignore, tail vacate, default construction with food spawn).
⏺ Write(snake/engine.py) Wrote 78 lines to snake/engine.py
"""Snake engine (milestone 1: grid and movement).
Pure game logic with no rendering or timing concerns. All randomness flows through the seeded random.Random passed to GameState. """ … +68 lines
Now let me verify with the loop-referee subagent as instructed.
⏺ loop-referee(Verify milestone 1 tests) Done (3 tool uses · 4.3k tokens · 1m 4s)
Milestone 1 is complete.
loop-referee output:
▎ PASS 10 — All 10 tests in tests/test_m1_movement.py passed (exit code 0, 10 passed in 0.01s). No failures.
What I implemented
Created snake/engine.py with the M1 scope (grid and movement):
- Direction enum — per SPEC (x right, y down).
- GameState — default construction spawns a length-2 snake with head at (width//2, height//2), tail one cell left, heading RIGHT; score=0, game_over=False; food spawned via the seeded rng on a non-body cell.
- step() — advances the head one cell, ignores 180° reversals (continues current direction = head minus neck), and vacates the tail unless pending_growth > 0.
Adhering to project rules: the engine imports no pygame, all randomness goes through the passed Random, and I stopped at M1 without touching M2–M5 (food/growth, collision, and eating logic are stubbed only as far as M1 requires — pending_growth is respected in step() but eating isn't wired up yet). The tests/ directory was not modified.
Ready to proceed to M2 (food and growth) when you are.
✻ Brewed for 1m 18s
Now do milestone 2
I'll read the M2 test to understand the exact requirements, then implement.
Read 1 file
The M2 tests need eating logic in step(). Let me update the engine.
⏺ Update(snake/engine.py) Added 6 lines
self.snake.insert(0, new_head)
# Eating: score and schedule growth, then respawn food off the body.
if new_head == self.food:
self.score += 1
self.pending_growth += 1
self.food = self._spawn_food()
# Tail vacates unless the snake is growing this tick.
if self.pending_growth > 0:
self.pending_growth -= 1
Now let me verify with the loop-referee subagent. Per project rules, I'll run the full suite to confirm M1 still passes too.
⏺ loop-referee(Verify milestone 2 tests) Done (1 tool use · 4.8k tokens · 12s)
Milestone 2 is complete.
loop-referee output:
▎ Result: 2 failed, 22 passed (24 total). ▎ - tests/test_m1_movement.py: all tests passed. ▎ - tests/test_m2_food.py: all tests passed. ▎ - The 2 failures are both in tests/test_m3_collision.py (test_tail_blocked_while_growing, test_wall_collision) — expected, since collision is milestone 3.
What I implemented
Added eating logic to step() in snake/engine.py:
- When the head advances onto the food cell: score += 1, pending_growth += 1, and a new food spawns via the seeded rng on a non-body cell (reusing the existing _spawn_food() helper).
- The existing pending_growth tail-withholding logic then handles growth — the tail is retained on the eating tick, so the snake grows by one.
All 10 M1 tests and all 8 M2 tests pass. The only failures are the M3 collision tests, which are the next milestone. Per the project rule (one milestone at a time), I stopped here.
Ready for M3 when you are.
✻ Churned for 41s
Now do milestone 3
Read 2 files
⏺ Update(snake/engine.py) Added 17 lines head = self.snake[0] new_head = (head[0] + dx, head[1] + dy)
# Growing this tick? The tail stays put if growth is pending or the
# head is about to eat. A withheld tail is a solid cell to collide on.
growing = self.pending_growth > 0 or new_head == self.food
# Wall collision: no wraparound.
if not (0 <= new_head[0] < self.width and
0 <= new_head[1] < self.height):
self.game_over = True
return
# Self collision: any body cell that is not vacating this tick. The
# tail (last segment) vacates unless the snake is growing.
blocking = self.snake if growing else self.snake[:-1]
if new_head in blocking:
self.game_over = True
return
self.snake.insert(0, new_head)
# Eating: score and schedule growth, then respawn food off the body.
Now let me verify with the loop-referee subagent.
⏺ loop-referee(Verify milestone 3 tests) Done (3 tool uses · 4.4k tokens · 18s)
Milestone 3 is complete.
loop-referee output:
▎ PASS — Full suite: 26 passed, 0 failed. tests/test_m3_collision.py: 4 tests collected, all 4 passed. Milestones 1–3 pass, and milestone 4 (determinism) also already passes — the entire suite is green.
What I implemented
Added collision detection to step() in snake/engine.py, applied before the snake mutates:
- Wall collision — if the new head is out of bounds (no wraparound), set game_over and return.
- Self collision — the new head hitting any body cell that is not vacating this tick. The key rule from SPEC: the tail vacates unless the snake is growing (pending growth or eating this tick), so:
- Not growing → tail vacates → blocking = self.snake[:-1] (moving into the vacating tail cell is legal).
- Growing → tail stays put → blocking = self.snake (that cell is now a collision).
When a collision is detected, the snake is left unmutated and game_over is set.
All 26 tests pass — and notably M4's determinism tests already pass, since randomness has flowed through the seeded rng throughout. That said, per the one-milestone-at-a-time rule I'll treat M4 as its own step: shall I formally verify/close out M4 (and check whether the score-exposure "speed hook" needs anything), or move straight to M5's pygame renderer?
✻ Crunched for 1m 13s
Now do milestone 4
Read 1 file
M4 is about determinism (all randomness through the seeded rng) and exposing score as a plain int — both already satisfied by the current engine, with no time/tick-rate logic in the engine (that's M5's renderer concern). No code changes are needed; the key is _spawn_food() builds its free-cell list in deterministic order before calling rng.choice. Let me formally verify with the referee per the rule.
⏺ loop-referee(Verify milestone 4 tests) Done (4 tool uses · 4.4k tokens · 18s)
Milestone 4 is complete.
loop-referee output:
▎ PASS 26 — Full suite: 26 collected, 26 passed, 0 failed (26 passed in 0.01s). tests/test_m4_determinism.py: 5 collected, 5 passed.
What M4 required
Determinism and the speed hook — and the engine already satisfied both, so no code changes were needed:
- Same seed → identical food sequence — all randomness flows through the seeded Random (per the project rule), and _spawn_food() builds its free-cell list in a fixed nested-range order before calling rng.choice, so two same-seed runs stay in perfect lockstep (initial food, respawns, scores, and full snake trajectory all match).
- Seed actually drives spawning — different seeds yield different food sequences (the rng isn't ignored).
- score exposed as a plain int — the renderer can derive its tick-rate ramp from it, while the engine itself knows nothing about time.
All 26 automated tests pass across M1–M4. The only remaining milestone is M5 — the pygame renderer (snake/render.py), which is human-verified with no automated tests, and which must keep the engine free of any pygame import. Want me to implement M5?
✻ Cogitated for 43s
Now do milestone 5
M5 is the pygame renderer — human-verified, no automated tests. Let me check the environment and spec details first.
Ran 1 shell command
pygame 2.6.1 is available. Now I'll write the renderer, keeping the engine pygame-free.
⏺ Write(snake/render.py) Wrote 142 lines to snake/render.py
"""Pygame renderer for the snake engine (milestone 5).
This module reads state from snake.engine.GameState and draws it; the engine itself never imports pygame and knows nothing about time. Arrow keys map to Direction, and the tick rate ramps up every 5 foods eaten. … +132 lines
No automated tests for M5, but I'll verify what I can: the engine stays pygame-free, the module imports cleanly, and the draw/step loop runs headless (SDL dummy driver) without errors. Let me also confirm the full suite still passes.
Ran 1 shell command
Now the full test suite to confirm nothing regressed, via the referee.
⏺ loop-referee(Confirm suite still green) Done (1 tool use · 3.7k tokens · 5s)
Milestone 5 is complete — all five milestones are now done.
Verification:
- loop-referee: PASS — 26 tests passed, 0 failures (M1–M4 still green; M5 has no automated tests by design).
- Engine stays pygame-free: grep confirms no pygame import in snake/engine.py.
- Headless smoke test (SDL dummy driver) exercised the real render code:
- Tick-rate ramp: [8, 8, 10, 10, 12, 24, 24] for scores [0, 4, 5, 9, 10, 40, 100] — bumps every 5 foods, capped at 24 fps. ✅
- Ran 4 ticks driving draw() each frame with no errors; ate food (score → 1). ✅
- Arrow-key mapping: up→UP, down→DOWN, left→LEFT, right→RIGHT. ✅
What I implemented
snake/render.py — a pygame renderer that reads engine state and draws it, with the engine remaining ignorant of pygame and time:
- Reads engine state — draws the grid, food, and snake (head highlighted), plus a HUD showing score and current speed.
- Arrow keys → Direction via KEY_TO_DIRECTION; the buffered next_direction is fed to gs.step(), and the engine's own reversal rule guards 180° turns.
- Tick-rate ramp — tick_rate(score) = BASE_FPS + (score // 5) * FPS_STEP, capped at MAX_FPS, fed to clock.tick(). The ramp lives entirely in the renderer, per SPEC.
- Game-over handling — shows a message and supports R to restart, Q/Esc to quit.
Run it with: python -m snake.render
Note: This is the human-verified milestone — the headless smoke test confirms the code runs and the logic is correct, but it can't validate the actual on-screen look and feel or key responsiveness. To fully close out M5, please run python -m snake.render (or .venv/bin/python -m snake.render) in a windowed session and confirm it plays as expected.
✻ Brewed for 1m 23s