Expose an explicitly unfinished Advanced preview in normal lobbies

Add room-creation and host lobby rules selectors, readiness reset, explicit
preview start and a persistent warning. Admit the six classic factions,
Tech Tokens with 3+ players and optional Stronghold Cards through genuine
setup. Keep expansion/module gates and complete-rules/publication criteria.

Persist the preview marker and enforce fresh native leaders, unchanged
piece custody and clean runtime/pacing state. Preserve private projections,
JSON continuation, exact room-entry retries and version/CAS protection.
Independent review resolved malformed leader, extra card-zone, missing
required-key and stale bot-deadline admission gaps.

Validation on the shared development tree: types, lint, 5169 offline
tests, build and 50 HTTP tests passed. The tree also contained the
separate deployment task's changes; this commit stages only preview scope.
All 57 base rosters completed real setup with each legal AI profile. Five
normal-preview-start games (2–6 seats) completed 1950 actions and
51 JSON restores without rejected actions; no strategy calibration.

Browser: actual create, host switch/readiness/Stronghold reset, explicit
start, exact private refresh, desktop and mobile warning checked. Retained
dev process stopped; backed up 1,629 saved games, restored server with all
unchanged, and resumed the same traitor choice into Storm. Baseline all-table
preservation retained 1626 rooms and 3442 seats; totals
now 1669 rooms and 3536 seats. No reset or automation.

Preview remains incomplete. Legacy unsupported expansion creation payloads
remain accepted for exact retry compatibility but cannot start. Existing
rules ambiguities and full visual acceptance remain open.

README.md

@@ -1,6 +1,6 @@
 # Dune — Arrakis Table
 
-An unofficial multiplayer adaptation of Gale Force Nine’s classic 2019 Dune, built with React, TypeScript, Vinext, and Cloudflare Workers/D1. **Development is ongoing; this is not yet a complete rules implementation.** Advanced and unfinished expansion starts remain disabled. Start with [current status](docs/CURRENT_STATUS.md) for implemented systems, remaining requirements and release gates; detailed historical evidence remains in the [implementation log](docs/IMPLEMENTATION_STATUS.md).
+An unofficial multiplayer adaptation of Gale Force Nine’s classic 2019 Dune, built with React, TypeScript, Vinext, and Cloudflare Workers/D1. **Development is ongoing; this is not yet a complete rules implementation.** The six classic factions can use a clearly labeled **Advanced preview**; unfinished expansion starts remain disabled. Start with [current status](docs/CURRENT_STATUS.md) for implemented systems, remaining requirements and release gates; detailed historical evidence remains in the [implementation log](docs/IMPLEMENTATION_STATUS.md).
 
 ## Run locally
 
@@ -14,6 +14,11 @@ npm run dev -- --host 0.0.0.0
 
 Open `http://localhost:3000`. Create a room, share its eight-character invitation, and add human or AI seats. The host can configure Easy, Medium, Hard and Brutal AI opponents. Current calibration demonstrates a substantially weaker Easy policy; it does not yet demonstrate a consistent ordering among the upper three levels.
 
+For Advanced play, choose **Rules → Advanced preview** before creating a room,
+or use the same selector as host in an existing base-game lobby. Everyone must
+ready again after changing rules, then the host chooses **Begin Advanced preview**.
+This mode is unfinished; see [preview scope and limits](docs/ADVANCED_PREVIEW.md).
+
 Before starting, open **Configure** on an AI seat to change its difficulty,
 faction or player circle without replacing it. Changes save immediately and
 clear human readiness. See [lobby AI configuration](docs/LOBBY_AI_CONFIGURATION.md).