Stagger cloud trail dissolution so tiles fade one at a time

Each cloud in the trail gets a slightly longer TTL than the one
before it (0.15s stagger). The origin cloud dissolves first, then
each subsequent tile follows. Two consecutive flights produce a
trail where the oldest clouds are already gone.

src/mudlib/commands/fly.py

@@ -14,8 +14,10 @@ world: Any = None
 # how far you fly
 FLY_DISTANCE = 5
 
-# how long cloud trail lingers (seconds)
+# origin cloud gets the base ttl, each step toward destination adds stagger.
-CLOUD_TTL = 2.0
+# trail visibly shrinks from origin toward the player, one tile at a time.
+CLOUD_TTL = 1.5
+CLOUD_STAGGER = 0.4  # seconds between each cloud's expiry
 
 # ANSI color for cloud trails
 CLOUD_COLOR = BOLD + BRIGHT_WHITE
@@ -68,10 +70,13 @@ async def cmd_fly(player: Player, args: str) -> None:
     dx, dy = delta
     start_x, start_y = player.x, player.y
 
-    # lay cloud trail at starting position and each intermediate step
+    # lay cloud trail at starting position and each intermediate step.
+    # origin cloud expires first, near-dest cloud lingers longest.
+    # the trail shrinks from behind toward the player over time.
     for step in range(FLY_DISTANCE):
         trail_x, trail_y = world.wrap(start_x + dx * step, start_y + dy * step)
-        add_effect(trail_x, trail_y, "~", CLOUD_COLOR, ttl=CLOUD_TTL)
+        ttl = CLOUD_TTL + step * CLOUD_STAGGER
+        add_effect(trail_x, trail_y, "~", CLOUD_COLOR, ttl=ttl)
 
     # move player to destination
     dest_x, dest_y = world.wrap(

tests/test_fly.py

@@ -219,17 +219,22 @@ async def test_cloud_trail_chars_are_tilde(player):
 
 
 @pytest.mark.asyncio
-async def test_cloud_trail_has_ttl(player):
+async def test_cloud_trail_dissolves_from_origin(player):
-    """Cloud effects should expire after roughly 2 seconds."""
+    """Origin cloud expires first, trail shrinks toward player."""
     players[player.name] = player
     player.flying = True
 
     before = time.monotonic()
     await fly.cmd_fly(player, "east")
 
-    for e in active_effects:
+    # effects are in path order (step 0..4)
-        remaining = e.expires_at - before
+    expiries = [e.expires_at for e in active_effects]
-        assert 1.5 <= remaining <= 2.5
+    # each should expire after the previous one (origin fades first)
+    for i in range(1, len(expiries)):
+        assert expiries[i] > expiries[i - 1]
+    # origin cloud ~1.5s, near-dest cloud ~1.5 + 4*0.4 = ~3.1s
+    assert 1.3 <= expiries[0] - before <= 1.7
+    assert 2.9 <= expiries[-1] - before <= 3.3
 
 
 @pytest.mark.asyncio