feat(data,sync,engine): per-mode best score and fastest win

Lifetime stats now also track best score and fastest win per game
mode (Classic, Zen, Challenge), additive on top of the existing
all-modes-combined `best_single_score` and `fastest_win_seconds`.
Time Attack is intentionally excluded — its scoring model is
session-level (count of wins inside a 10-minute window) so a
per-game best wouldn't compose. Daily Challenge inherits Classic
scoring and contributes through the Classic row.

- `solitaire_sync::StatsSnapshot` gains six fields (`{mode}_best_score`,
  `{mode}_fastest_win_seconds` × {Classic, Zen, Challenge}). All are
  `#[serde(default)]` so older save files load cleanly to zeros.
- `solitaire_sync::merge` propagates the per-mode bests through the
  same max/min logic as the global counterparts.
- `solitaire_data::StatsExt::update_per_mode_bests` is the engine's
  entry point — called from `update_stats_on_win` alongside the
  existing `update_on_win`.
- Stats overlay grows a "Per-mode bests" section with three rows
  (Classic / Zen / Challenge) tagged with `PerModeBestsRow`. Empty
  rows render an em-dash, matching the first-launch zero-state
  treatment used by the primary cells.
- 3 new tests cover the rendering, the Classic-mode update path,
  and the Zen-mode update path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

solitaire_sync/src/merge.rs

@@ -109,10 +109,45 @@ fn merge_stats(
         best_single_score: local.best_single_score.max(remote.best_single_score),
         draw_one_wins: local.draw_one_wins.max(remote.draw_one_wins),
         draw_three_wins: local.draw_three_wins.max(remote.draw_three_wins),
+        // Per-mode bests. Bests take max; fastest times take a *zero-aware*
+        // min — see [`min_ignore_zero`] for the rationale (0 means "no win
+        // yet" for these fields, unlike the lifetime `fastest_win_seconds`
+        // which uses `u64::MAX` as its sentinel).
+        classic_best_score: local.classic_best_score.max(remote.classic_best_score),
+        classic_fastest_win_seconds: min_ignore_zero(
+            local.classic_fastest_win_seconds,
+            remote.classic_fastest_win_seconds,
+        ),
+        zen_best_score: local.zen_best_score.max(remote.zen_best_score),
+        zen_fastest_win_seconds: min_ignore_zero(
+            local.zen_fastest_win_seconds,
+            remote.zen_fastest_win_seconds,
+        ),
+        challenge_best_score: local.challenge_best_score.max(remote.challenge_best_score),
+        challenge_fastest_win_seconds: min_ignore_zero(
+            local.challenge_fastest_win_seconds,
+            remote.challenge_fastest_win_seconds,
+        ),
         last_modified: Utc::now(),
     }
 }
 
+/// Zero-aware minimum: returns the smaller of `a` and `b`, but treats `0` as
+/// "no value recorded yet" so `min_ignore_zero(0, x) == x`.
+///
+/// The lifetime `fastest_win_seconds` field uses `u64::MAX` as its "no wins"
+/// sentinel (see [`StatsSnapshot::default`]) and so a plain `min` works for
+/// it. The per-mode `*_fastest_win_seconds` fields, on the other hand, are
+/// `#[serde(default)]` — and `u64`'s default is 0, not `u64::MAX`. Using a
+/// straight `min` would therefore wrongly resolve "one side has a real time,
+/// the other has no win" to 0. This helper preserves the real time instead.
+fn min_ignore_zero(a: u64, b: u64) -> u64 {
+    match (a, b) {
+        (0, x) | (x, 0) => x,
+        _ => a.min(b),
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Achievements
 // ---------------------------------------------------------------------------
@@ -875,6 +910,87 @@ mod tests {
         );
     }
 
+    // -----------------------------------------------------------------------
+    // Per-mode bests merge
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn merge_per_mode_best_takes_max() {
+        // Classic best score: 1000 vs 2000 → 2000. Mirror behaviour for
+        // `best_single_score` so per-mode follows the same rule.
+        let mut local = default_payload();
+        local.stats.classic_best_score = 1000;
+        let mut remote = default_payload();
+        remote.stats.classic_best_score = 2000;
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.classic_best_score, 2000);
+    }
+
+    #[test]
+    fn merge_per_mode_best_takes_max_for_zen_and_challenge() {
+        let mut local = default_payload();
+        local.stats.zen_best_score = 800;
+        local.stats.challenge_best_score = 5000;
+        let mut remote = default_payload();
+        remote.stats.zen_best_score = 1500;
+        remote.stats.challenge_best_score = 3000;
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.zen_best_score, 1500);
+        assert_eq!(merged.stats.challenge_best_score, 5000);
+    }
+
+    #[test]
+    fn merge_per_mode_fastest_ignores_zero() {
+        // Local has no Zen win (zen_fastest = 0); remote has 180s.
+        // Straight min(0, 180) would return 0 — wrong. The merge must
+        // preserve the real time.
+        let local = default_payload();
+        let mut remote = default_payload();
+        remote.stats.zen_fastest_win_seconds = 180;
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.zen_fastest_win_seconds, 180);
+    }
+
+    #[test]
+    fn merge_per_mode_fastest_takes_min_when_both_present() {
+        // When both sides have real times, the merge takes the smaller —
+        // mirroring the lifetime `fastest_win_seconds` behaviour.
+        let mut local = default_payload();
+        local.stats.classic_fastest_win_seconds = 240;
+        let mut remote = default_payload();
+        remote.stats.classic_fastest_win_seconds = 120;
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.classic_fastest_win_seconds, 120);
+    }
+
+    #[test]
+    fn merge_per_mode_fastest_both_zero_stays_zero() {
+        // Neither side has a win — the field must remain 0 rather than
+        // accidentally becoming non-zero.
+        let local = default_payload();
+        let remote = default_payload();
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.classic_fastest_win_seconds, 0);
+        assert_eq!(merged.stats.zen_fastest_win_seconds, 0);
+        assert_eq!(merged.stats.challenge_fastest_win_seconds, 0);
+    }
+
+    #[test]
+    fn merge_per_mode_fastest_local_real_remote_zero() {
+        // Symmetric to `merge_per_mode_fastest_ignores_zero`: local has the
+        // real time, remote is the zero-side. The merge must keep local's
+        // value rather than flooring to 0.
+        let mut local = default_payload();
+        local.stats.challenge_fastest_win_seconds = 300;
+        let remote = default_payload();
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(merged.stats.challenge_fastest_win_seconds, 300);
+    }
+
     #[test]
     fn merge_longest_streak_never_below_current_streak() {
         // If a payload's `daily_challenge_longest_streak` was never written

solitaire_sync/src/stats.rs

@@ -33,6 +33,56 @@ pub struct StatsSnapshot {
     pub draw_one_wins: u32,
     /// Wins achieved in Draw-Three mode.
     pub draw_three_wins: u32,
+
+    // -----------------------------------------------------------------
+    // Per-mode bests
+    //
+    // These mirror `best_single_score` / `fastest_win_seconds` but
+    // narrowed to one [`solitaire_core::game_state::GameMode`]. They are
+    // additive: lifetime totals continue to track across all modes, and
+    // legacy `stats.json` files load to 0 for every new field via
+    // `#[serde(default)]`.
+    //
+    // Time-Attack and Daily-Challenge are intentionally absent here:
+    // - Time Attack has its own session-level scoring (count of wins
+    //   inside a 10-minute window); a per-game best wouldn't compose.
+    // - Daily Challenge uses Classic scoring rules and so already
+    //   contributes to `classic_*` here.
+    //
+    // Sentinel for `*_fastest_win_seconds` is `0` (not `u64::MAX`),
+    // because legacy files deserialise unknown fields to the type's
+    // `Default::default()` — and `u64::default()` is 0. The merge logic
+    // and the UI must therefore treat 0 as "no win recorded yet".
+    // -----------------------------------------------------------------
+
+    /// Best single score achieved in Classic mode (Draw-One or Draw-Three).
+    /// 0 means "no Classic win yet".
+    #[serde(default)]
+    pub classic_best_score: u32,
+
+    /// Fastest Classic-mode win time, in seconds. 0 means "no Classic win yet".
+    #[serde(default)]
+    pub classic_fastest_win_seconds: u64,
+
+    /// Best single score achieved in Zen mode. Zen has no time pressure but
+    /// scoring is still on, so players who care about it still play for a high.
+    /// 0 means "no Zen win yet".
+    #[serde(default)]
+    pub zen_best_score: u32,
+
+    /// Fastest Zen-mode win time, in seconds. 0 means "no Zen win yet".
+    #[serde(default)]
+    pub zen_fastest_win_seconds: u64,
+
+    /// Best single score achieved in Challenge mode (the hardest mode — separate
+    /// leaderboard). 0 means "no Challenge win yet".
+    #[serde(default)]
+    pub challenge_best_score: u32,
+
+    /// Fastest Challenge-mode win time, in seconds. 0 means "no Challenge win yet".
+    #[serde(default)]
+    pub challenge_fastest_win_seconds: u64,
+
     /// Wall-clock time of the last modification (used for conflict detection).
     pub last_modified: DateTime<Utc>,
 }
@@ -51,6 +101,12 @@ impl Default for StatsSnapshot {
             best_single_score: 0,
             draw_one_wins: 0,
             draw_three_wins: 0,
+            classic_best_score: 0,
+            classic_fastest_win_seconds: 0,
+            zen_best_score: 0,
+            zen_fastest_win_seconds: 0,
+            challenge_best_score: 0,
+            challenge_fastest_win_seconds: 0,
             last_modified: DateTime::UNIX_EPOCH,
         }
     }
@@ -147,4 +203,20 @@ mod tests {
         assert_eq!(s.win_streak_best, 7, "best streak must not be reduced on abandon");
         assert_eq!(s.win_streak_current, 0);
     }
+
+    #[test]
+    fn per_mode_fields_default_to_zero() {
+        // The new per-mode fields must default to 0 — both in the explicit
+        // `Default` impl and (because of `#[serde(default)]`) for any
+        // legacy payload that omits them. The legacy-JSON deserialise
+        // round-trip lives in `solitaire_data::stats` where `serde_json`
+        // is in scope.
+        let s = StatsSnapshot::default();
+        assert_eq!(s.classic_best_score, 0);
+        assert_eq!(s.classic_fastest_win_seconds, 0);
+        assert_eq!(s.zen_best_score, 0);
+        assert_eq!(s.zen_fastest_win_seconds, 0);
+        assert_eq!(s.challenge_best_score, 0);
+        assert_eq!(s.challenge_fastest_win_seconds, 0);
+    }
 }