# Handoff: AI Phase 1 (Casual bot) shipped

## Session Metadata

- Created: 2026-04-28 ~19:15 UTC
- Project: /home/claude/bin/blind_chess
- Branch: `feat/ai-player-phase-1-casual` (16 commits ahead of main; pending merge as final step of this handoff)
- Repo: `git.sethpc.xyz/Seth/blind_chess`
- Live URL: **https://chess.sethpc.xyz** (Phase 1 deployed and verified)

## Handoff Chain

- **Continues from**: [2026-04-28-170713-ai-player-spec.md](./2026-04-28-170713-ai-player-spec.md) — AI player spec written and approved.
- **Supersedes**: None.

## Current State Summary

Phase 1 of the AI player feature (Casual bot) is **deployed and live**. Playing vs a Casual bot is now an option from the landing page, alongside the existing "play with a friend" flow.

This session executed `docs/superpowers/plans/2026-04-28-ai-player-phase-1-casual.md` via subagent-driven development: 13 tasks, dispatched as fresh subagents per task with two-stage review (spec compliance + code quality). Several tasks surfaced real plan bugs that subagents fixed inline; the most consequential reversal was during Task 11 (self-play harness): the hand-rolled scoring algorithm in `CasualBrain` lost to a random-move baseline 7-7 in 100-game self-play, far below the spec's ≥80% acceptance bar. Solution: swapped vanilla-mode CasualBrain to delegate to `js-chess-engine` (level 2, randomness=30); blind mode kept the heuristic. Casual now wins 96-97% vs Random in vanilla, in both colors.

## Architecture Overview (what's deployed)

- **`packages/server/src/bot/`** — new module:
  - `brain.ts` — `Brain` interface, `BrainInput`/`BrainAction`/`CandidateMove`/`AttemptHistoryEntry` types. `BrainInput.fen` set ONLY in vanilla mode (preserves view-filter invariant).
  - `candidates.ts` — `legalCandidates(game, color)`. Vanilla: `chess.js .moves({verbose: true})`. Blind: `geometricMoves` over own pieces + promotion expansion.
  - `casual-brain.ts` — `CasualBrain implements Brain`. Vanilla: delegates to `js-chess-engine` at level 2; blind: heuristic scoring (capture proxy / development / center / advance). Promotion default: queen. Draw response based on own material count.
  - `driver.ts` — `BotDriver` per-game orchestrator. Mutex via `decideInFlight`, retry cap of 5, dispatches via `handleCommit`/announce, on game end calls `brain.dispose?.()`.
  - `index.ts` — public re-exports.
- **`packages/server/src/game-end.ts`** — extracted from `ws.ts`: `endGame`/`finalizeIfEnded`. Both `ws.ts` and `bot/driver.ts` use it.
- **`packages/server/src/games.ts`** — bot driver registry (`attachBotDriver`, `getBotDriver`, `disposeBotDriver`). `createGame` accepts optional `vsAi: { brain }` and fills the bot's slot with a synthetic player slot (random token, no socket). `pruneFinished` cleans the registry.
- **`packages/server/src/state.ts`** — `Game` gains optional `aiOpponent?: { color; brain }` (informational) and required `lastBroadcastIdx: { w: number; b: number }` (per-color watermark for slice broadcasting).
- **`packages/server/src/ws.ts`** — refactored: `pokeBot(game)` helper called after every state-mutating handler; `broadcastSinceLast(game)` replaces the old `broadcastNewAnnouncements` (slices `game.announcements` from each color's watermark). Handlers are async; router uses `void` casts to discard handler Promises.
- **`packages/server/src/server.ts`** — `POST /api/games` handles `vsAi: { brain: 'casual' }`: instantiates `CasualBrain` + `BotDriver`, attaches to registry. `vsAi.brain === 'recon'` returns 503 (Phase 2 not implemented). `joinUrl: null` for AI games.
- **`packages/shared/src/protocol.ts`** — `CreateGameRequest.vsAi`, `CreateGameResponse.joinUrl: string | null`, `aiOpponent` on `joined` and `update` server messages.
- **`packages/server/src/validation.ts`** — Zod schema for `vsAi`.
- **Client (`packages/client/`)** — landing page split into two sections (friend / vs computer). In-game UI shows a "Casual bot" badge in the topbar; turn label says "Casual bot is moving…" when bot's turn. The "Opponent disconnected" banner is suppressed for AI games.
- **`scripts/selfplay.ts`** — operator CLI. `pnpm selfplay --white casual --black random --games 100 --mode vanilla`. Reports W/B/D/MaxPly/Err and end-reason histogram. Supports `--transcripts` for per-game logs.

## Phase 1 Acceptance — Met

| Check | Result |
|---|---|
| 100 Casual self-play vanilla games complete | ✅ Err=0 across all runs |
| Median ply 20-200 in self-play | ✅ avgPly~52 (engine vs random), ~116 (Casual vs Casual) |
| Casual ≥80% vs Random, both colors | ✅ 97% as W, 96% as B |
| All unit + integration tests pass | ✅ 75/75 (21 shared + 54 server) |
| Live smoke checklist | ✅ /api/health, AI game creation, recon→503, no journald errors |
| Branch merged + deployed | ⏳ Pending merge (final step of this session) |

## Critical Files

| File | Status | Notes |
|---|---|---|
| `docs/superpowers/specs/2026-04-28-ai-player-design.md` | Unchanged | Original spec; still the source of truth for Phase 2. |
| `docs/superpowers/plans/2026-04-28-ai-player-phase-1-casual.md` | Unchanged | Phase 1 plan; can be archived or marked "executed" if useful. |
| `CLAUDE.md` | ✅ Updated | "Current State" reflects Phase 1 deployed; "Key files" lists new bot module. |
| `DECISIONS.md` | ✅ Updated | New "Phase 1 implementation outcomes" section; the previous "Stockfish deferred" entry is now strikethrough (partial supersede — using `js-chess-engine` instead). |
| `packages/server/src/bot/` | ✅ New | Brain, BotDriver, CasualBrain, candidates, index. |
| `packages/server/src/game-end.ts` | ✅ New | Extracted endGame/finalizeIfEnded. |
| `scripts/selfplay.ts` | ✅ New | Self-play harness. Run via `pnpm selfplay`. |
| `.secrets.baseline` | ✅ Refreshed | The previous baseline was stale (~6087 lines → 8196 after refresh). pnpm-lock.yaml integrity hashes for js-chess-engine were tripping the secret-detection hook. |

## Decisions Made (highlights — full list in DECISIONS.md)

- **CasualBrain reversal**: vanilla mode now delegates to `js-chess-engine` at level 2. Hand-rolled scorer lost to random — empirically broken. Engine swap brought it to 96-97% vs random.
- **`BrainInput.fen` is vanilla-only**: blind mode omits the FEN to preserve the view-filter invariant. The engine cannot smuggle opponent positions past the security boundary.
- **Blind mode keeps the heuristic**: a chess engine isn't useful when the bot only sees its own pieces. That gap is what Phase 2 (Recon) addresses with belief-state-from-announcements.
- **Bot-slot tokens are randomized**: not a fixed placeholder. Closes a hijack vector caught in code review.
- **`endGame`/`finalizeIfEnded` extracted to `game-end.ts`**: both ws and driver need to set finished state; duplication risk eliminated.
- **`pokeBot → broadcastSinceLast` order is load-bearing**: the bot's response (move + announcements) must be in `game.announcements` before broadcasting, so the human sees the bot's reply in the same WS message they receive after their own move.

## Immediate Next Steps

1. **Merge `feat/ai-player-phase-1-casual` to `main`** (final step of this handoff).

   ```bash
   git checkout main
   git merge --ff-only feat/ai-player-phase-1-casual || git merge --no-ff feat/ai-player-phase-1-casual
   git push origin main
   ```

2. **Soak Phase 1 for a few days of real play** before starting Phase 2. Watch for:
   - Bot-driver errors in journald (`journalctl -u blind-chess | grep "bot driver error"`).
   - Mid-game crashes or stuck games.
   - User feedback on Casual's strength (too weak / too strong / fine).

3. **When ready, write Phase 2 plan** — `docs/superpowers/plans/2026-04-28-ai-player-phase-2-recon.md` against the existing spec. Phase 2 reuses the `Brain` and `BotDriver` infrastructure unchanged; new pieces are `OllamaClient`, `ollama-endpoints` (preflight + failover), `prompt`, `parse`, `ReconBrain`, plus `aiInfo` protocol field, `'ai_unavailable'` end reason, post-game reasoning reveal UI.

## Blockers / Open Questions

- **Casual at level 2 may be too strong for some users.** Beats random 96-97% which is the intended acceptance bar, but a careful human is supposed to win against Casual. If users report Casual is unbeatable, drop to level 1. If users report it's trivial, raise to level 3. (`packages/server/src/bot/casual-brain.ts:33` — change the default in `CasualOpts`.)
- **Blind mode self-play games are very short** (avgPly=16, all resignations). The heuristic exhausts its retry cap (5) when the bot picks a move that can't legally proceed in blind mode. This is functional but observation: blind Casual is much weaker than vanilla Casual. Consider raising retry cap or improving heuristic if blind Casual feels broken in real play.
- **`js-chess-engine` declares `engines: { node: '>=24' }`** but works on Node 22.22.2. Engines is advisory by default. If a future Node update breaks it, pin to v1.x of the package (`npm i js-chess-engine@^1.0.0`) — older API but compatible.

## Deferred Items (Phase 2 work)

All from the original AI spec, untouched:
- `ReconBrain` (gemma4:26b chat agent on steel141 RTX 3090 Ti, pve197 V100 fallback).
- Mid-game GPU failover, preflight, AI-unavailable end state.
- Persistent chat history per game; post-game reasoning reveal UI.
- `aiInfo` protocol field (model + GPU + host).
- Acceptance bar: Recon wins ≥60% over 50 Recon-vs-Casual self-play games.

## Important Context for Future Sessions

- **The bot's `BoardView` is the only egress to the engine, in vanilla mode.** This invariant is preserved structurally: the FEN is set in `BrainInput` only when `mode === 'vanilla'`. Phase 2 ReconBrain will not need this field at all (it gets the view + announcements only — same input shape as a human player who can't see the FEN of the actual game).
- **`Casual` and `Recon` brains are both architecturally instances of `Brain`.** Phase 2 just adds another `Brain` implementation against the same `BotDriver`. The driver's mutex / retry / dispatch / dispose lifecycle does NOT need changes.
- **Watermark advance only on successful dispatch** (in `BotDriver.runDecisionCycle`). On retry, the brain still sees the FSM's rejection announcement in `newAnnouncements`. This matters for ReconBrain (Phase 2) which uses announcements as evidence; CasualBrain ignores them.
- **`scripts/selfplay.ts` is the canonical evaluation tool**. Phase 2 will extend it to support `--white recon --black casual` etc. The harness sets `game.aiOpponent = undefined; game.status = 'active'` after `createGame` returns — that's how it transitions out of "waiting" without a hello.
- **The pre-commit hook is `detect-secrets-hook --baseline .secrets.baseline`** in `/home/claude/.config/git/hooks/pre-commit`. If you add a new dep and pnpm-lock.yaml hashes get flagged, run `detect-secrets scan > .secrets.baseline` to refresh.

## Files Modified / Added This Session

| File | Change |
|---|---|
| (new) `packages/server/src/bot/{brain,candidates,casual-brain,driver,index}.ts` | The bot module (~600 LoC). |
| (new) `packages/server/src/game-end.ts` | Extracted from ws.ts. |
| (new) `packages/server/test/unit/bot/{candidates,casual-brain,driver}.test.ts` | 27 unit tests. |
| (new) `packages/server/test/integration/ai-game-casual.test.ts` | 5 integration tests. |
| (new) `scripts/selfplay.ts` | Operator CLI. |
| (new) `docs/superpowers/plans/2026-04-28-ai-player-phase-1-casual.md` | The plan. |
| `packages/server/src/state.ts`, `games.ts`, `validation.ts`, `server.ts`, `ws.ts` | Wired up. |
| `packages/shared/src/protocol.ts` | Added `vsAi`, `aiOpponent`, nullable `joinUrl`. |
| `packages/client/src/lib/Landing.svelte`, `Game.svelte`, `stores/game.svelte.ts` | UI. |
| `package.json`, `pnpm-lock.yaml`, `packages/server/package.json` | Added `js-chess-engine`, `tsx`. |
| `CLAUDE.md`, `DECISIONS.md` | Context updates. |
| `.secrets.baseline` | Refreshed. |

## Environment State

- **CT 690 / blind-chess.service:** running. `systemctl is-active` returns `active`. Uptime measured from the deploy-restart at 2026-04-28 ~19:14 UTC.
- **Active processes:** none session-relevant. The deploy was a normal restart of the systemd unit.
- **Environment variables:** none added/changed.
- **Secrets:** none added; `.secrets.baseline` was refreshed to a clean state (the old one had ~4500 lines of stale per-file entries).

## Related Resources

- Live URL: https://chess.sethpc.xyz — Phase 1 live.
- Repo: https://git.sethpc.xyz/Seth/blind_chess — `feat/ai-player-phase-1-casual` branch (pending merge to main).
- Spec: `docs/superpowers/specs/2026-04-28-ai-player-design.md`.
- Plan: `docs/superpowers/plans/2026-04-28-ai-player-phase-1-casual.md`.
- Decisions: `DECISIONS.md` "AI / computer player" section + new "Phase 1 implementation outcomes" subsection.
- Project identity: `CLAUDE.md`.
- Prior handoffs: `2026-04-28-170713-ai-player-spec.md`, `2026-04-28-152000-mvp-deployed.md`, `2026-04-28-104344-spec-approved-ready-for-plan.md`, `2026-04-28-kickoff.md`.

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**Security Reminder**: This handoff describes Phase 1 deployment; no credentials, secrets, or sensitive endpoints are exposed in the handoff or the deployed code. The bot uses no external services in Phase 1 (Phase 2 will add Ollama endpoints).