Fix #28: stash stats periodically so beforeunload sends real scores

Module._analyticsLastStats was only set when the C shutdown path ran
(analytics_session_end). When a player closes the browser tab mid-game,
the beforeunload fallback found _analyticsLastStats null and sent
score 0 to the backend.

Add analytics_stash_stats() which updates _analyticsLastStats every
~1 second during gameplay. The beforeunload handler now always has
current stats to send.

src/game/analytics.c

@@ -167,6 +167,20 @@ EM_JS(void, js_analytics_send_end, (int score, int level_reached,
     doEnd(sid, endReason, score, level_reached, lives_used, duration_secs);
 });
 
+/* Stash current stats into Module._analyticsLastStats so the
+ * beforeunload fallback sends real data if the tab is closed. */
+EM_JS(void, js_analytics_stash_stats, (int score, int level_reached,
+                                       int lives_used, int duration_secs), {
+    if (!Module._analyticsUrl || !Module._analyticsSessionId) return;
+    Module._analyticsLastStats = JSON.stringify({
+        score: score,
+        level_reached: level_reached > 0 ? level_reached : 1,
+        lives_used: lives_used,
+        duration_seconds: duration_secs,
+        end_reason: 'quit'
+    });
+});
+
 /* ── C wrappers ─────────────────────────────────────────────────── */
 
 void analytics_init(void) {
@@ -188,6 +202,16 @@ void analytics_session_end(GameStats *stats, const char *end_reason) {
     );
 }
 
+void analytics_stash_stats(GameStats *stats) {
+    stats_update_score(stats);
+    js_analytics_stash_stats(
+        stats->score,
+        stats->levels_completed > 0 ? stats->levels_completed : 1,
+        stats->deaths,
+        (int)stats->time_elapsed
+    );
+}
+
 #else
 /* ── Non-WASM stubs ─────────────────────────────────────────────── */
 
@@ -202,4 +226,8 @@ void analytics_session_end(GameStats *stats, const char *end_reason) {
     (void)end_reason;
 }
 
+void analytics_stash_stats(GameStats *stats) {
+    (void)stats;
+}
+
 #endif /* __EMSCRIPTEN__ */

src/game/analytics.h

@@ -15,4 +15,9 @@ void analytics_session_start(void);
  * end_reason: "death", "quit", "timeout", or "completed". */
 void analytics_session_end(GameStats *stats, const char *end_reason);
 
+/* Stash current stats for the beforeunload fallback so that
+ * closing the browser tab sends real data instead of zeros.
+ * Call periodically from the game loop. No-op on non-WASM. */
+void analytics_stash_stats(GameStats *stats);
+
 #endif /* JNR_ANALYTICS_H */

src/main.c

@@ -55,6 +55,8 @@ static int s_mars_depth = 0;
 /* ── Analytics / stats tracking ── */
 static GameStats s_stats;
 static bool      s_session_active = false;
+static int       s_stash_tick = 0; /* frames since last analytics stash */
+#define ANALYTICS_STASH_INTERVAL 60 /* stash stats every ~1 second */
 
 /* ── Pause menu state ── */
 #define PAUSE_ITEM_COUNT 3
@@ -262,6 +264,7 @@ static void begin_session(void) {
     stats_set_active(&s_stats);
     analytics_session_start();
     s_session_active = true;
+    s_stash_tick = 0;
 }
 
 static void end_session(const char *reason) {
@@ -581,6 +584,12 @@ static void game_update(float dt) {
     /* Accumulate play time */
     if (s_session_active) {
         s_stats.time_elapsed += dt;
+
+        /* Periodically stash stats for the beforeunload fallback. */
+        if (++s_stash_tick >= ANALYTICS_STASH_INTERVAL) {
+            s_stash_tick = 0;
+            analytics_stash_stats(&s_stats);
+        }
     }
 
     /* Check for level exit transition */