Weather changes on time; repeat rolls lengthen the spell

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

game.py

@@ -1563,6 +1563,7 @@ def tick(world: dict, now: float, rng: random.Random | None = None) -> bool:
         _happenings_hour(world, city["last_tick"], rng)
         _city_hour(world, city["last_tick"])
         changed = True
+    changed = advance_weather(world, now, rng) or changed
     changed = _happenings_tracks(world, now, rng) or changed
     construction = city["construction"]
     if construction and construction["labour"] >= construction["needed"]:
@@ -2134,6 +2135,30 @@ def _roll_weather(world: dict, now: float, rng: random.Random, current: str | No
     return _pick(SEASON_WEATHER[season(world, now)["index"]], rng)
 
 
+def advance_weather(world: dict, now: float, rng: random.Random) -> bool:
+    """Change the weather when its spell ends. Returns True if it changed."""
+    weather = world["city"]["weather"]
+    if now < weather["until"]:
+        return False
+    while now >= weather["until"]:
+        weather["kind"] = weather["next"]
+        _plan_spell(world, weather, rng)
+    return True
+
+
+def _plan_spell(world: dict, weather: dict, rng: random.Random) -> None:
+    """Set how long the current weather lasts and what follows. Rolls that keep the
+    same weather lengthen the spell, so `until` is when it really changes."""
+    for _ in range(3):
+        weather["until"] += rng.uniform(4, 8) * HOUR / speed(world)
+        weather["next"] = _roll_weather(world, weather["until"], rng, weather["kind"])
+        if weather["next"] != weather["kind"]:
+            return
+    # Three spells of the same is long enough: something else comes next.
+    weights = SEASON_WEATHER[season(world, weather["until"])["index"]]
+    weather["next"] = _pick({kind: w for kind, w in weights.items() if kind != weather["kind"]}, rng)
+
+
 def _modifier_sources(world: dict) -> list[dict]:
     city = world["city"]
     sources = [WEATHER[city["weather"]["kind"]]] + city["effects"]
@@ -2437,11 +2462,7 @@ def hire_mercenaries(world: dict, player: dict, now: float) -> str | None:
 def _happenings_hour(world: dict, now: float, rng: random.Random) -> None:
     """Weather, firewood, thieves and expiries, once per game hour."""
     city = world["city"]
-    weather = city["weather"]
-    if now >= weather["until"]:
-        weather["kind"] = weather["next"]
-        weather["until"] = now + rng.uniform(4, 8) * HOUR / speed(world)
-        weather["next"] = _roll_weather(world, weather["until"], rng, weather["kind"])
+    advance_weather(world, now, rng)
     city["effects"] = [e for e in city["effects"] if e["until"] > now]
     for problem in list(city["problems"]):
         if problem.get("until") and problem["until"] <= now: