Rewrite the backend in Rust with Axum

Replace the Python/kaya server in server/ with a Rust Cargo workspace of
three crates mirroring the old layout: tavolo-platform (lobby API, live-game
store, websocket endpoint, deadline scheduler, stats/Elo, OIDC sessions),
tavolo-scopone (pure scopone scientifico rules plus the platform adapter)
and tavolo-app (composition root and the `tavolo` binary with
serve/migrate/backfill-elo).

The HTTP and WebSocket contracts, error messages, Redis key layout and
Postgres schema are unchanged, so the existing web/ frontend and in-flight
games keep working. Notable differences: sessions are JSON under
tavolo:session: (Python pickle sessions invalidate once), LOGGING_CONFIG is
ignored in favour of RUST_LOG, DATABASE_URL must be Postgres, sqlx migrations
replace aerich, and OpenTelemetry exports Rust process metrics instead of
CPython gc metrics (no Postgres/Redis client instrumentation).

Docker Compose and the Kubernetes manifest now run the single Rust image
(embedded migrations, /static and /assets served by the app); the release CI
keeps building server/Dockerfile. The full test suite (scopone rules,
platform store/deadlines/stats/websockets, OIDC login flow, scopone e2e) is
ported and runs with cargo test --workspace; Redis/Postgres integration tests
are gated on TEST_REDIS_URL/TEST_DATABASE_URL.

server/crates/tavolo-scopone/tests/plugin.rs

@@ -0,0 +1,483 @@
+//! `ScoponeEngine` adapter tests: the platform contract over the pure rules.
+//!
+//! Ported from `tavolo-scopone/tests/test_plugin.py`.
+
+use serde_json::{json, Map, Value};
+use tavolo_platform::engine::GameSession;
+use tavolo_platform::errors::Error;
+use tavolo_platform::{GameEngine, Seat};
+use tavolo_scopone::engine as rules;
+use tavolo_scopone::state::{Card, ScoponeState, PHASE_FINISHED, PHASE_HAND_END, PHASE_PLAYING};
+use tavolo_scopone::ScoponeEngine;
+
+fn opts(value: Value) -> Map<String, Value> {
+    value.as_object().unwrap().clone()
+}
+
+fn empty() -> Map<String, Value> {
+    Map::new()
+}
+
+fn capitalize(name: &str) -> String {
+    let mut chars = name.chars();
+    match chars.next() {
+        Some(first) => first.to_uppercase().collect::<String>() + chars.as_str(),
+        None => String::new(),
+    }
+}
+
+fn base_session(engine: &ScoponeEngine) -> GameSession {
+    let mut session = GameSession::new("s1", engine.id(), "CODE01");
+    session.creator_sub = "alice".to_string();
+    session.players = vec![Seat {
+        user_sub: "alice".to_string(),
+        display_name: "Alice".to_string(),
+        team: None,
+    }];
+    session
+}
+
+fn make_session(engine: &ScoponeEngine, options: Map<String, Value>) -> Result<GameSession, Error> {
+    let mut session = base_session(engine);
+    engine.create(&mut session, &options)?;
+    Ok(session)
+}
+
+fn started(engine: &ScoponeEngine, options: Map<String, Value>) -> GameSession {
+    let mut session = make_session(engine, options).unwrap();
+    for name in ["bob", "carol", "dave"] {
+        engine.join(&mut session, name, &capitalize(name)).unwrap();
+    }
+    session
+}
+
+fn state(session: &GameSession) -> &ScoponeState {
+    session
+        .state
+        .as_ref()
+        .unwrap()
+        .downcast_ref::<ScoponeState>()
+        .unwrap()
+}
+
+fn state_mut(session: &mut GameSession) -> &mut ScoponeState {
+    session
+        .state
+        .as_mut()
+        .unwrap()
+        .downcast_mut::<ScoponeState>()
+        .unwrap()
+}
+
+fn err_message(error: &Error) -> String {
+    error
+        .as_game()
+        .map(|game| game.message.clone())
+        .unwrap_or_default()
+}
+
+/// Extract the error from a failed `make_session` without requiring
+/// `GameSession: Debug` (which `unwrap_err` would).
+fn session_error(result: Result<GameSession, Error>) -> Error {
+    match result {
+        Ok(_) => panic!("expected an error"),
+        Err(error) => error,
+    }
+}
+
+/// Play legal moves (and acknowledge hand ends) until the match finishes.
+fn drive_to_finish(engine: &ScoponeEngine, session: &mut GameSession) -> usize {
+    let mut moves = 0;
+    while !engine.is_finished(session) && moves < 200_000 {
+        let (action, sub, payload): (&str, String, Map<String, Value>) = {
+            let st = state(session);
+            if st.phase == PHASE_HAND_END {
+                let player = st
+                    .players
+                    .iter()
+                    .find(|player| !st.acked.contains(&player.seat))
+                    .unwrap();
+                ("ack", player.sub.clone(), Map::new())
+            } else {
+                let player = st
+                    .players
+                    .iter()
+                    .find(|player| player.seat == st.turn)
+                    .unwrap();
+                let played = player.hand[0].clone();
+                let options = rules::legal_captures(&st.table, played.clone(), st.asso_pigliatutto);
+                let mut payload = Map::new();
+                payload.insert("card".to_string(), json!(played.code()));
+                if let Some(option) = options.first() {
+                    payload.insert(
+                        "capture".to_string(),
+                        json!(option.iter().map(Card::code).collect::<Vec<_>>()),
+                    );
+                }
+                ("play", player.sub.clone(), payload)
+            }
+        };
+        engine
+            .handle_action(session, &sub, action, &payload)
+            .unwrap();
+        moves += 1;
+    }
+    moves
+}
+
+// -- create ----------------------------------------------------------------
+
+#[test]
+fn create_seats_creator_on_team_a() {
+    let engine = ScoponeEngine::default();
+    let session = make_session(&engine, empty()).unwrap();
+    assert_eq!(Some("A".to_string()), session.players[0].team);
+    let st = state(&session);
+    assert_eq!(11, st.target_score);
+    assert!(st.napola);
+}
+
+#[test]
+fn create_options() {
+    let engine = ScoponeEngine::default();
+    let session =
+        make_session(&engine, opts(json!({"target_score": 16, "napola": false}))).unwrap();
+    let st = state(&session);
+    assert_eq!(16, st.target_score);
+    assert!(!st.napola);
+    assert!(!st.asso_pigliatutto);
+}
+
+#[test]
+fn create_asso_pigliatutto_option() {
+    let engine = ScoponeEngine::default();
+    let session = make_session(&engine, opts(json!({"asso_pigliatutto": true}))).unwrap();
+    assert!(state(&session).asso_pigliatutto);
+}
+
+#[test]
+fn create_rejects_bad_options() {
+    let engine = ScoponeEngine::default();
+    assert_eq!(
+        "target_score must be between 1 and 100",
+        err_message(&session_error(make_session(
+            &engine,
+            opts(json!({"target_score": 0}))
+        )))
+    );
+    assert_eq!(
+        "target_score must be an integer",
+        err_message(&session_error(make_session(
+            &engine,
+            opts(json!({"target_score": "eleven"}))
+        )))
+    );
+    assert_eq!(
+        "napola must be a boolean",
+        err_message(&session_error(make_session(
+            &engine,
+            opts(json!({"napola": "yes"}))
+        )))
+    );
+    assert_eq!(
+        "asso_pigliatutto must be a boolean",
+        err_message(&session_error(make_session(
+            &engine,
+            opts(json!({"asso_pigliatutto": "yes"}))
+        )))
+    );
+}
+
+#[test]
+fn timeouts_come_from_the_engine() {
+    let engine = ScoponeEngine::new(7, 9);
+    let session = make_session(&engine, empty()).unwrap();
+    let st = state(&session);
+    assert_eq!(7, st.turn_timeout);
+    assert_eq!(9, st.hand_ack_timeout);
+}
+
+// -- join ------------------------------------------------------------------
+
+#[test]
+fn join_assigns_teams_and_starts() {
+    let engine = ScoponeEngine::default();
+    let mut session = make_session(&engine, empty()).unwrap();
+    assert!(engine.in_lobby(&session));
+    for (name, team) in [("bob", "B"), ("carol", "A"), ("dave", "B")] {
+        engine.join(&mut session, name, &capitalize(name)).unwrap();
+        assert_eq!(Some(team.to_string()), session.players.last().unwrap().team);
+    }
+    assert!(!engine.in_lobby(&session));
+    assert_eq!(PHASE_PLAYING, state(&session).phase);
+}
+
+#[test]
+fn join_errors() {
+    let engine = ScoponeEngine::default();
+    let mut session = make_session(&engine, empty()).unwrap();
+    assert_eq!(
+        "already joined this game",
+        err_message(&engine.join(&mut session, "alice", "Alice").unwrap_err())
+    );
+    for name in ["bob", "carol", "dave"] {
+        engine.join(&mut session, name, &capitalize(name)).unwrap();
+    }
+    // The lobby filled up and the match started: late joins and even re-joins
+    // are rejected as "already started".
+    assert_eq!(
+        "game has already started",
+        err_message(&engine.join(&mut session, "erin", "Erin").unwrap_err())
+    );
+    assert_eq!(
+        "game has already started",
+        err_message(&engine.join(&mut session, "alice", "Alice").unwrap_err())
+    );
+}
+
+// -- actions ---------------------------------------------------------------
+
+#[test]
+fn unknown_action_rejected() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    assert!(engine
+        .handle_action(&mut session, "alice", "dance", &Map::new())
+        .is_err());
+}
+
+#[test]
+fn play_validates_payload() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    assert!(engine
+        .handle_action(&mut session, "bob", "play", &opts(json!({"card": 42})))
+        .is_err());
+    assert!(engine
+        .handle_action(&mut session, "bob", "play", &Map::new())
+        .is_err());
+    assert!(engine
+        .handle_action(
+            &mut session,
+            "bob",
+            "play",
+            &opts(json!({"card": "01D", "capture": "02C"}))
+        )
+        .is_err());
+}
+
+#[test]
+fn invalid_card_code_is_illegal_move() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    let error = engine
+        .handle_action(&mut session, "bob", "play", &opts(json!({"card": "nope"})))
+        .unwrap_err();
+    assert_eq!("invalid card code", err_message(&error));
+}
+
+#[test]
+fn finished_match_rejects_actions() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, opts(json!({"target_score": 1})));
+    drive_to_finish(&engine, &mut session);
+    assert!(engine.is_finished(&session));
+    let error = engine
+        .handle_action(&mut session, "alice", "play", &opts(json!({"card": "01D"})))
+        .unwrap_err();
+    assert_eq!("the match is over", err_message(&error));
+}
+
+// -- views -----------------------------------------------------------------
+
+#[test]
+fn view_for_hides_other_hands() {
+    let engine = ScoponeEngine::default();
+    let session = started(&engine, empty());
+    let view = engine.view_for(&session, "alice");
+    let players = view["players"].as_array().unwrap();
+    let alice = players.iter().find(|p| p["seat"] == 0).unwrap();
+    let bob = players.iter().find(|p| p["seat"] == 1).unwrap();
+    assert!(alice.get("hand").is_some());
+    assert!(bob.get("hand").is_none());
+    // The envelope is the platform's job, not the view's.
+    assert!(view.get("id").is_none());
+    assert!(view.get("join_code").is_none());
+    assert!(view.get("game_type").is_none());
+}
+
+#[test]
+fn lobby_view() {
+    let engine = ScoponeEngine::default();
+    let session = make_session(&engine, opts(json!({"target_score": 16}))).unwrap();
+    let lobby = engine.lobby_view(&session);
+    assert_eq!(json!("lobby"), lobby["phase"]);
+    assert_eq!(json!(16), lobby["target_score"]);
+    assert_eq!(json!(true), lobby["napola"]);
+    assert_eq!(json!(false), lobby["asso_pigliatutto"]);
+}
+
+// -- serialization ---------------------------------------------------------
+
+#[test]
+fn state_roundtrip() {
+    let engine = ScoponeEngine::default();
+    let session = started(&engine, empty());
+    let state_value = engine
+        .state_to_json(session.state.as_ref().unwrap().as_ref())
+        .unwrap();
+    let restored = engine.state_from_json(&state_value).unwrap();
+    let restored = restored.downcast_ref::<ScoponeState>().unwrap();
+    assert_eq!(state(&session).phase, restored.phase);
+    assert_eq!(state(&session).turn, restored.turn);
+    assert_eq!(
+        state(&session)
+            .players
+            .iter()
+            .map(|p| p.sub.clone())
+            .collect::<Vec<_>>(),
+        restored
+            .players
+            .iter()
+            .map(|p| p.sub.clone())
+            .collect::<Vec<_>>()
+    );
+}
+
+// -- deadlines -------------------------------------------------------------
+
+#[test]
+fn no_deadline_in_lobby() {
+    let engine = ScoponeEngine::default();
+    let session = make_session(&engine, empty()).unwrap();
+    assert!(engine.next_deadline(&session).unwrap().is_none());
+}
+
+#[test]
+fn turn_deadline_and_revalidation() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    let deadline = engine.next_deadline(&session).unwrap().unwrap();
+    assert_eq!("turn", deadline.kind);
+    // A forged token is stale.
+    assert!(engine
+        .fire_deadline(&mut session, "turn", "turn:1:1:0")
+        .is_err());
+    let turn_before = state(&session).turn;
+    engine
+        .fire_deadline(&mut session, &deadline.kind, &deadline.token)
+        .unwrap();
+    assert_ne!(turn_before, state(&session).turn);
+}
+
+#[test]
+fn stale_deadline_after_play() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    let deadline = engine.next_deadline(&session).unwrap().unwrap();
+    // A play lands in time: the armed deadline is overtaken.
+    let (sub, payload) = {
+        let st = state(&session);
+        let player = st.players.iter().find(|p| p.seat == st.turn).unwrap();
+        let played = player.hand[0].clone();
+        let options = rules::legal_captures(&st.table, played.clone(), st.asso_pigliatutto);
+        let mut payload = Map::new();
+        payload.insert("card".to_string(), json!(played.code()));
+        if let Some(option) = options.first() {
+            payload.insert(
+                "capture".to_string(),
+                json!(option.iter().map(Card::code).collect::<Vec<_>>()),
+            );
+        }
+        (player.sub.clone(), payload)
+    };
+    engine
+        .handle_action(&mut session, &sub, "play", &payload)
+        .unwrap();
+    assert!(engine
+        .fire_deadline(&mut session, &deadline.kind, &deadline.token)
+        .is_err());
+}
+
+#[test]
+fn hand_end_deadline_advances() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    {
+        let st = state_mut(&mut session);
+        st.phase = PHASE_HAND_END.to_string();
+        st.hand_end_deadline = Some(tavolo_platform::datetime::to_iso(
+            tavolo_platform::datetime::now() + chrono::Duration::seconds(60),
+        ));
+    }
+    let deadline = engine.next_deadline(&session).unwrap().unwrap();
+    assert_eq!("hand_end", deadline.kind);
+    engine
+        .fire_deadline(&mut session, &deadline.kind, &deadline.token)
+        .unwrap();
+    let st = state(&session);
+    assert_eq!(PHASE_PLAYING, st.phase);
+    assert_eq!(2, st.hand_number);
+}
+
+// -- results ---------------------------------------------------------------
+
+#[test]
+fn result_of_finished_match() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, opts(json!({"target_score": 1})));
+    drive_to_finish(&engine, &mut session);
+    let result = engine.result(&session).unwrap();
+    assert_eq!(2, result.teams.len());
+    assert!(result.winner_team == 0 || result.winner_team == 1);
+    assert_eq!(4, result.players.len());
+    let winner_name = if result.winner_team == 0 { "A" } else { "B" };
+    for player in &result.players {
+        assert_eq!(player.won, player.team.as_deref() == Some(winner_name));
+    }
+    assert!(result.summary.get("team_a_score").is_some());
+    assert!(result.summary.get("hands_played").is_some());
+}
+
+#[test]
+fn result_requires_finished_match() {
+    let engine = ScoponeEngine::default();
+    let session = started(&engine, empty());
+    assert!(engine.result(&session).is_err());
+}
+
+#[test]
+fn game_over_view() {
+    let engine = ScoponeEngine::default();
+    let mut session = started(&engine, empty());
+    {
+        let st = state_mut(&mut session);
+        st.phase = PHASE_FINISHED.to_string();
+        st.winner = Some(1);
+        st.scores = vec![3, 11];
+    }
+    let over = engine.game_over_view(&session, "alice");
+    assert_eq!(json!({"A": 3, "B": 11}), over["scores"]);
+    assert_eq!(json!("B"), over["winner"]);
+}
+
+#[test]
+fn registry_metadata() {
+    let engine = ScoponeEngine::default();
+    assert_eq!("scopone_scientifico", engine.id());
+    assert_eq!(4, engine.min_players());
+    assert_eq!(4, engine.max_players());
+    let schema = engine.options_schema();
+    assert!(schema["properties"]["target_score"].is_object());
+    assert!(schema["properties"]["napola"].is_object());
+    assert!(schema["properties"]["asso_pigliatutto"].is_object());
+    // Byte-compatible option schema: descriptions and defaults match Python.
+    assert_eq!(
+        json!("Score the napola rule; a full denari sweep wins the match"),
+        schema["properties"]["napola"]["description"]
+    );
+    assert_eq!(
+        json!("Score the asso pigliatutto rule; an ace sweeps the whole table (no scopa)"),
+        schema["properties"]["asso_pigliatutto"]["description"]
+    );
+}