Add Portal class with target zone and coordinates

Portals are non-portable Things that exist in zones and define
transitions to other zones via target coordinates.

src/mudlib/portal.py

@@ -0,0 +1,25 @@
+"""Portal — a transition point between zones."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from mudlib.thing import Thing
+
+
+@dataclass
+class Portal(Thing):
+    """A portal connecting zones.
+
+    Portals are non-portable Things that exist in zones and define
+    transitions to other zones via target coordinates.
+    """
+
+    target_zone: str = ""
+    target_x: int = 0
+    target_y: int = 0
+
+    def __post_init__(self) -> None:
+        """Force portals to be non-portable."""
+        self.portable = False
+        super().__post_init__()

tests/test_portal.py

@@ -0,0 +1,96 @@
+"""Tests for the Portal class."""
+
+from mudlib.object import Object
+from mudlib.portal import Portal
+from mudlib.thing import Thing
+from mudlib.zone import Zone
+
+# --- construction ---
+
+
+def test_portal_creation_minimal():
+    """Portal can be created with just a name."""
+    p = Portal(name="portal")
+    assert p.name == "portal"
+    assert p.location is None
+    assert p.target_zone == ""
+    assert p.target_x == 0
+    assert p.target_y == 0
+
+
+def test_portal_creation_with_target():
+    """Portal can be created with target zone and coordinates."""
+    p = Portal(name="gateway", target_zone="dungeon", target_x=5, target_y=10)
+    assert p.target_zone == "dungeon"
+    assert p.target_x == 5
+    assert p.target_y == 10
+
+
+def test_portal_is_thing_subclass():
+    """Portal inherits from Thing."""
+    p = Portal(name="portal")
+    assert isinstance(p, Thing)
+
+
+def test_portal_is_object_subclass():
+    """Portal inherits from Object (via Thing)."""
+    p = Portal(name="portal")
+    assert isinstance(p, Object)
+
+
+def test_portal_always_non_portable():
+    """Portal is always non-portable (cannot be picked up)."""
+    p = Portal(name="portal")
+    assert p.portable is False
+
+
+def test_portal_forced_non_portable():
+    """Portal forces portable=False even if explicitly set True."""
+    # Even if we try to make it portable, it should be forced to False
+    p = Portal(name="portal", portable=True)
+    assert p.portable is False
+
+
+def test_portal_inherits_description():
+    """Portal can have a description (from Thing)."""
+    p = Portal(name="gateway", description="a shimmering portal")
+    assert p.description == "a shimmering portal"
+
+
+def test_portal_inherits_aliases():
+    """Portal can have aliases (from Thing)."""
+    p = Portal(name="gateway", aliases=["portal", "gate"])
+    assert p.aliases == ["portal", "gate"]
+
+
+def test_portal_in_zone():
+    """Portal can exist in a zone with coordinates."""
+    terrain = [["." for _ in range(10)] for _ in range(10)]
+    zone = Zone(name="test", width=10, height=10, terrain=terrain)
+    p = Portal(
+        name="gateway",
+        location=zone,
+        x=3,
+        y=7,
+        target_zone="dungeon",
+        target_x=5,
+        target_y=5,
+    )
+    assert p.location is zone
+    assert p.x == 3
+    assert p.y == 7
+    assert p in zone.contents
+
+
+def test_portal_rejects_contents():
+    """Portal cannot accept other objects (uses Thing's default behavior)."""
+    p = Portal(name="portal")
+    obj = Object(name="rock")
+    assert p.can_accept(obj) is False
+
+
+def test_portal_rejects_things():
+    """Portal cannot accept things."""
+    p = Portal(name="portal")
+    thing = Thing(name="sword")
+    assert p.can_accept(thing) is False