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.

docs/ADVANCED_PREVIEW.md

@@ -0,0 +1,69 @@
+# Advanced preview
+
+The user explicitly authorized a clearly labeled unfinished Advanced mode on
+21 September 2026. This changes access to the existing development game, not
+the rules-completion or publication criteria.
+
+## Select and start
+
+1. On the home page, choose **Rules → Advanced preview**, then **Create a room**.
+2. Invite players or add AI seats. The preview supports two through six of the
+   six classic factions: Atreides, Harkonnen, Fremen, Emperor, Guild and Bene Gesserit.
+3. Optionally enable **Tech Tokens** with at least three players, or
+   **Stronghold Cards** in the lobby.
+4. Each human chooses **Ready for Advanced preview**. The host chooses
+   **Begin Advanced preview**.
+
+The host can also change **Rules** in an existing base-game lobby. Changing modes
+clears human readiness; native AI seats remain ready. Switching to Basic removes
+unused Stronghold Cards and keeps Tech Tokens. Rules cannot change after setup
+starts. Selecting Advanced on the home page clears expansion selections, which
+are outside this preview. Joining a room uses that room's existing rules.
+
+The warning remains visible throughout Advanced play, including older Advanced
+development saves. Games use the existing room save, reconnect and private seat
+system. Basic remains the default.
+
+## Admission and saved behavior
+
+Normal room creation already stores `advanced: boolean`; the same request format
+and exact tab retry are retained. The host-only lobby action
+`{type: 'rules', advanced: boolean}` changes the mode. The ordinary start action
+must contain `advancedPreview: true` for Advanced; a bare start remains rejected.
+Only a successful explicit start writes `Game.advancedPreview: true`.
+`GameView.advancedPreview` projects the marker as a boolean.
+
+Start calls the genuine shared setup pipeline, including prediction, Traitors,
+starting forces, advisors, elites and the starting Treachery deal at their normal
+stages. The live API never dispatches a test/audit initializer. Fresh-lobby and
+unused-module checks prevent accidental redealing. Restored preview markers must
+still match their supported mode and roster. Mode changes, starts and ordinary
+continuation retain the existing version/CAS fence and private views.
+
+Expansion factions/decks, Homeworlds, Nexus, Discoveries, Leader Skills, the Ecaz
+Treachery variant and separate audit profiles remain rejected by normal starts.
+Enabling Advanced cannot bypass those gates. For compatibility with exact older
+create retries, the create API still accepts the pre-existing expansion lobby
+format; those unsupported lobbies cannot start and have no expansion-removal
+control yet. The preview creation UI prevents that combination. No pending ruling is resolved by
+this access change; see the [decision index](RULE_DECISIONS.md).
+
+## Evidence and limits
+
+- `advanced-preview.test.ts`: normal explicit starts, strict authority/admission,
+  readiness, Basic fallback, genuine setup for all 57 base rosters with each of
+  four existing legal AI profiles, card/force custody, JSON and private views.
+- `advanced-preview-controls.test.ts`: visible mode/warning/host controls and
+  exact Advanced create-request restoration.
+- `advanced-preview-recovery.test.ts`: production room SQL, fresh module reload,
+  both private seats, unchanged rejected requests and start/rules CAS races.
+- `advanced-preview-http.test.ts`: normal authenticated endpoints, explicit
+  opt-in, origin/authority checks, readiness, duplicate start and refresh.
+
+The private checkpoint directory records final check/build/HTTP results, ordinary
+preview-start complete-game samples, browser checks and saved-game preservation.
+These are development samples, not AI calibration or complete interaction coverage.
+Advanced base powers and timing audits remain unfinished, including the recorded
+Guild/special-Karama boundaries and advisor interactions. Stronghold Cards and
+Tech Tokens retain their existing implementation limits. Full visual acceptance,
+complete rules compliance and publication remain open.