Engine: multi-player drop-out-and-continue with a per-game tile disposition (remove default / return), resigned seats skipped and excluded from the win, leaver rack never revealed; 2-player behaviour unchanged.
New domains (service/store, no HTTP yet): internal/social (friend request/accept graph, per-user blocks, per-game chat with nudge as a message kind, content filter via mvdan.cc/xurls/v2 + leet/separator normaliser + phone heuristic) and internal/lobby (in-memory variant-keyed matchmaking pool, friend-game invitations invite->accept with lazy 7-day expiry). account gains profile editing and the email confirm-code flow (Mailer seam: SMTP or log mailer).
Migration 00003_social.sql + regenerated jet. main wires the new services into the server (accessors for the Stage 6 handlers); robot substitution stays in Stage 5, REST/stream/push in Stage 6/8. Docs (PLAN, ARCHITECTURE, FUNCTIONAL+ru, TESTING, README) updated.
backend/internal/engine wraps the sibling scrabble-solver library in-process:
- Registry: versioned DAWG load via dafsa.Load, keyed by (variant, dict_version),
latest-per-variant; English / Russian / Эрудит handled uniformly.
- Bag: own deterministic, seeded tile bag with Draw + Return (for exchanges),
since the solver's self-play bag cannot return tiles.
- Game: pure rules engine — deal, play/pass/exchange/resign, refill, per-move
scoring, turn order, and end-condition detection (empty bag + empty rack, six
scoreless turns, resignation) with end-game rack adjustment.
- decode/ReplayBoard: dictionary-independent MoveRecords and board replay via
scrabble.Apply (no internal/encoding), realising ARCHITECTURE §9.1.
Wiring: go.work gains "replace scrabble-solver => ../scrabble-solver"; backend
requires scrabble-solver (placeholder) and github.com/iliadenisov/dafsa directly.
Both Go CI workflows clone the public solver sibling (master HEAD, no token) and
set BACKEND_DICT_DIR.
Docs: ARCHITECTURE §5/§14, TESTING engine layer, backend README, and PLAN
refinements + deferred TODOs (publish/version solver; split engine vs dictionary
generator).
Ilia Denisov