Port 4 medium opcodes to hybrid z-machine interpreter

Implements op_print_addr, op_print_num, op_ret, and op_show_status following
TDD approach with tests first. Each opcode now properly decodes/prints text,
handles signed numbers, returns from routines, or acts as a no-op as appropriate.

src/mudlib/zmachine/zcpu.py

@@ -405,8 +405,9 @@ class ZCpu:
         self._write_result(val, store_addr=variable)
 
     def op_print_addr(self, string_byte_address):
-        """TODO: Write docstring here."""
-        raise ZCpuNotImplemented
+        """Print the z-encoded string at the given byte address."""
+        text = self._string.get(string_byte_address)
+        self._ui.screen.write(text)
 
     def op_call_1s(self, routine_address):
         """Call the given routine and store the return value."""
@@ -421,9 +422,10 @@ class ZCpu:
         shortname = self._objects.get_shortname(obj)
         self._ui.screen.write(shortname)
 
-    def op_ret(self, *args):
-        """TODO: Write docstring here."""
-        raise ZCpuNotImplemented
+    def op_ret(self, value):
+        """Return from the current routine with the given value."""
+        pc = self._stackmanager.finish_routine(value)
+        self._opdecoder.program_counter = pc
 
     def op_jump(self, offset):
         """Jump unconditionally to the given branch offset.  This
@@ -535,8 +537,8 @@ class ZCpu:
         self._ui.screen.write("\n")
 
     def op_show_status(self, *args):
-        """TODO: Write docstring here."""
-        raise ZCpuNotImplemented
+        """Update status line (V3 only). No-op in this implementation."""
+        pass
 
     def op_verify(self, *args):
         """TODO: Write docstring here."""
@@ -592,9 +594,10 @@ class ZCpu:
         """Output the given ZSCII character."""
         self._ui.screen.write(self._string.zscii.get([char]))
 
-    def op_print_num(self, *args):
-        """TODO: Write docstring here."""
-        raise ZCpuNotImplemented
+    def op_print_num(self, value):
+        """Print a signed 16-bit number as text."""
+        signed_value = self._make_signed(value)
+        self._ui.screen.write(str(signed_value))
 
     def op_random(self, n):
         """Generate a random number, or seed the PRNG.

tests/test_zmachine_opcodes.py

@@ -250,6 +250,44 @@ class ZMachineOpcodeTests(TestCase):
         # Stack should be empty
         self.assertEqual(len(self.stack.stack), 0)
 
+    def test_op_print_addr(self):
+        """Test print_addr decodes and prints text at byte address."""
+        # Configure mock string decoder to return a known string
+        self.cpu._string.get = Mock(return_value="Hello, world!")
+        # Print text at address 0x5000
+        self.cpu.op_print_addr(0x5000)
+        # Should have called string decoder with the address
+        self.cpu._string.get.assert_called_once_with(0x5000)
+        # Should have written the decoded text
+        self.ui.screen.write.assert_called_once_with("Hello, world!")
+
+    def test_op_print_num_positive(self):
+        """Test print_num prints positive number."""
+        self.cpu.op_print_num(42)
+        self.ui.screen.write.assert_called_once_with("42")
+
+    def test_op_print_num_negative(self):
+        """Test print_num prints negative number."""
+        # -1 as unsigned 16-bit is 65535
+        self.cpu.op_print_num(65535)
+        self.ui.screen.write.assert_called_once_with("-1")
+
+    def test_op_print_num_zero(self):
+        """Test print_num prints zero."""
+        self.cpu.op_print_num(0)
+        self.ui.screen.write.assert_called_once_with("0")
+
+    def test_op_ret(self):
+        """Test ret returns from routine with value."""
+        self.cpu.op_ret(42)
+        # Should have set PC to caller's address (0x1000 from mock)
+        self.assertEqual(self.cpu._opdecoder.program_counter, 0x1000)
+
+    def test_op_show_status(self):
+        """Test show_status is a no-op (V3 only, not needed in MUD)."""
+        # Should just not raise an exception
+        self.cpu.op_show_status()
+
 
 class MockObjectParser:
     """Mock object parser for testing CPU opcodes."""