Wire op_restore to QuetzalParser and filesystem

Implement V3 restore opcode:
- Add QuetzalParser.load_from_bytes() to parse save data from memory
- Wire op_restore to call filesystem.restore_game() and parse result
- Validate IFhd matches current story (release/serial/checksum)
- Restore dynamic memory, call stack, and program counter
- Branch true on success, false on failure/cancellation

Fix IFF chunk padding bug:
- Add padding byte to odd-length chunks in QuetzalWriter
- Ensures proper chunk alignment for parser compatibility

Add comprehensive tests:
- Branch false when filesystem returns None
- Branch false without zmachine reference
- Branch true on successful restore
- Verify memory state matches saved values
- Handle malformed save data gracefully

src/mudlib/zmachine/quetzal.py

@@ -294,6 +294,71 @@ class QuetzalParser:
         debugging and test verification."""
         return self._last_loaded_metadata
 
+    def load_from_bytes(self, data):
+        """Parse Quetzal data from raw bytes (instead of a file).
+
+        Used by op_restore when filesystem.restore_game() returns raw bytes.
+        """
+        import io
+
+        self._last_loaded_metadata = {}
+
+        if len(data) < 12:
+            raise QuetzalUnrecognizedFileFormat
+
+        # Validate FORM header
+        if data[0:4] != b"FORM":
+            raise QuetzalUnrecognizedFileFormat
+
+        # Read total length
+        self._len = (data[4] << 24) + (data[5] << 16) + (data[6] << 8) + data[7]
+        log(f"Total length of FORM data is {self._len}")
+        self._last_loaded_metadata["total length"] = self._len
+
+        # Validate IFZS type
+        if data[8:12] != b"IFZS":
+            raise QuetzalUnrecognizedFileFormat
+
+        # Create a BytesIO object to use with chunk module
+        self._file = io.BytesIO(data)
+        self._file.seek(12)  # Skip FORM header, length, and IFZS type
+
+        log("Parsing chunks from byte data")
+        try:
+            while 1:
+                c = chunk.Chunk(self._file)
+                chunkname = c.getname()
+                chunksize = c.getsize()
+                chunk_data = c.read(chunksize)
+                log(f"** Found chunk ID {chunkname}: length {chunksize}")
+                self._last_loaded_metadata[chunkname] = chunksize
+
+                if chunkname == b"IFhd":
+                    self._parse_ifhd(chunk_data)
+                elif chunkname == b"CMem":
+                    self._parse_cmem(chunk_data)
+                elif chunkname == b"UMem":
+                    self._parse_umem(chunk_data)
+                elif chunkname == b"Stks":
+                    self._parse_stks(chunk_data)
+                elif chunkname == b"IntD":
+                    self._parse_intd(chunk_data)
+                elif chunkname == b"AUTH":
+                    self._parse_auth(chunk_data)
+                elif chunkname == b"(c) ":
+                    self._parse_copyright(chunk_data)
+                elif chunkname == b"ANNO":
+                    self._parse_anno(chunk_data)
+                else:
+                    # spec says to ignore and skip past unrecognized chunks
+                    pass
+
+        except EOFError:
+            pass
+
+        self._file.close()
+        log("Finished parsing Quetzal data.")
+
     def load(self, savefile_path):
         """Parse each chunk of the Quetzal file at SAVEFILE_PATH,
         initializing associated zmachine subsystems as needed."""
@@ -543,6 +608,9 @@ class QuetzalWriter:
             result.append((size >> 8) & 0xFF)
             result.append(size & 0xFF)
             result.extend(chunk_data)
+            # IFF chunks must be padded to even byte boundaries
+            if size % 2 == 1:
+                result.append(0)  # padding byte
             log(f"  Added {chunk_id} chunk ({size} bytes)")
 
         # Write nested chunks

src/mudlib/zmachine/zcpu.py

@@ -586,9 +586,40 @@ class ZCpu:
     def op_restore(self, *args):
         """Restore game state from file (V3 - branch on success).
 
-        Currently always fails because QuetzalWriter is not yet functional,
+        Uses QuetzalParser to load save data from filesystem,
-        so there are no valid save files to restore.
+        validates it matches current story, and restores memory/stack/PC.
+        Branches true on success, false on failure.
         """
+        if self._zmachine is None:
+            # Can't restore without zmachine reference
+            self._branch(False)
+            return
+
+        from .quetzal import QuetzalParser
+
+        try:
+            # Get save data from filesystem
+            save_data = self._ui.filesystem.restore_game()
+            if save_data is None:
+                # User cancelled or no save file available
+                self._branch(False)
+                return
+
+            # Parse the save data
+            parser = QuetzalParser(self._zmachine)
+            parser.load_from_bytes(save_data)
+
+            # QuetzalParser already:
+            # - Validated IFhd matches current story (release/serial/checksum)
+            # - Replaced dynamic memory via _parse_cmem or _parse_umem
+            # - Replaced stack manager via _parse_stks
+            # - Set program counter via _parse_ifhd
+
+            # Success!
+            self._branch(True)
+        except Exception as e:
+            # Any error during restore process = failure
+            log(f"Restore failed with exception: {e}")
             self._branch(False)
 
     def op_restore_v4(self, *args):

tests/test_quetzal_writer.py

@@ -0,0 +1,417 @@
+"""Tests for QuetzalWriter Stks chunk generation."""
+
+
+class TestStksChunkGeneration:
+    """Test Stks chunk generation and serialization."""
+
+    def test_empty_stack_serialization(self):
+        """Test serializing an empty stack (just the bottom sentinel)."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZStackManager
+
+        # Setup: create a mock zmachine with only the bottom sentinel
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Empty stack should serialize to empty bytes (no frames)
+        assert result == b""
+
+    def test_single_frame_no_locals_no_stack(self):
+        """Test serializing a single routine frame with no locals or stack values."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create a routine with no locals and no stack values
+        routine = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x1234,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[],
+            stack=[],
+        )
+        stack_manager.push_routine(routine)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Expected format:
+        # Bytes 0-2: return_pc = 0x1234 (24-bit big-endian)
+        # Byte 3: flags = 0 (0 local vars)
+        # Byte 4: varnum = 0 (which variable gets return value)
+        # Byte 5: argflag = 0
+        # Bytes 6-7: eval_stack_size = 0
+        expected = bytes(
+            [
+                0x00,
+                0x12,
+                0x34,  # return_pc (24-bit)
+                0x00,  # flags (0 locals)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x00,  # eval_stack_size = 0
+            ]
+        )
+
+        assert result == expected
+
+    def test_single_frame_with_locals(self):
+        """Test serializing a frame with local variables."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create a routine with 3 local variables
+        routine = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x2000,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0x1111, 0x2222, 0x3333],
+            stack=[],
+        )
+        stack_manager.push_routine(routine)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Expected format:
+        # Bytes 0-2: return_pc = 0x2000
+        # Byte 3: flags = 3 (3 local vars in bits 0-3)
+        # Byte 4: varnum = 0x00
+        # Byte 5: argflag = 0
+        # Bytes 6-7: eval_stack_size = 0
+        # Bytes 8-13: three local vars (0x1111, 0x2222, 0x3333)
+        expected = bytes(
+            [
+                0x00,
+                0x20,
+                0x00,  # return_pc
+                0x03,  # flags (3 locals)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x00,  # eval_stack_size = 0
+                0x11,
+                0x11,  # local_var[0]
+                0x22,
+                0x22,  # local_var[1]
+                0x33,
+                0x33,  # local_var[2]
+            ]
+        )
+
+        assert result == expected
+
+    def test_single_frame_with_stack_values(self):
+        """Test serializing a frame with evaluation stack values."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create a routine with stack values but no locals
+        routine = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x3000,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[],
+            stack=[0xABCD, 0xEF01],
+        )
+        stack_manager.push_routine(routine)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Expected format:
+        # Bytes 0-2: return_pc = 0x3000
+        # Byte 3: flags = 0 (0 locals)
+        # Byte 4: varnum = 0x00
+        # Byte 5: argflag = 0
+        # Bytes 6-7: eval_stack_size = 2
+        # Bytes 8-11: two stack values
+        expected = bytes(
+            [
+                0x00,
+                0x30,
+                0x00,  # return_pc
+                0x00,  # flags (0 locals)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x02,  # eval_stack_size = 2
+                0xAB,
+                0xCD,  # stack[0]
+                0xEF,
+                0x01,  # stack[1]
+            ]
+        )
+
+        assert result == expected
+
+    def test_single_frame_full(self):
+        """Test serializing a frame with both locals and stack values."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create a routine with 2 locals and 3 stack values
+        routine = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x4567,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0x0001, 0x0002],
+            stack=[0x1000, 0x2000, 0x3000],
+        )
+        stack_manager.push_routine(routine)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        expected = bytes(
+            [
+                0x00,
+                0x45,
+                0x67,  # return_pc
+                0x02,  # flags (2 locals)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x03,  # eval_stack_size = 3
+                0x00,
+                0x01,  # local_var[0]
+                0x00,
+                0x02,  # local_var[1]
+                0x10,
+                0x00,  # stack[0]
+                0x20,
+                0x00,  # stack[1]
+                0x30,
+                0x00,  # stack[2]
+            ]
+        )
+
+        assert result == expected
+
+    def test_multiple_nested_frames(self):
+        """Test serializing multiple nested routine frames."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create first routine
+        routine1 = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x1000,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0xAAAA],
+            stack=[0xBBBB],
+        )
+        stack_manager.push_routine(routine1)
+
+        # Create second routine (nested)
+        routine2 = ZRoutine(
+            start_addr=0x6000,
+            return_addr=0x2000,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0xCCCC],
+            stack=[0xDDDD],
+        )
+        stack_manager.push_routine(routine2)
+
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Expected: two frames concatenated
+        expected = bytes(
+            [
+                # Frame 1
+                0x00,
+                0x10,
+                0x00,  # return_pc
+                0x01,  # flags (1 local)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x01,  # eval_stack_size = 1
+                0xAA,
+                0xAA,  # local_var[0]
+                0xBB,
+                0xBB,  # stack[0]
+                # Frame 2
+                0x00,
+                0x20,
+                0x00,  # return_pc
+                0x01,  # flags (1 local)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x01,  # eval_stack_size = 1
+                0xCC,
+                0xCC,  # local_var[0]
+                0xDD,
+                0xDD,  # stack[0]
+            ]
+        )
+
+        assert result == expected
+
+    def test_bottom_frame_zero_return_pc(self):
+        """Test that a bottom/dummy frame with return_pc=0 is handled correctly."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+        stack_manager = ZStackManager(zmachine._mem)
+
+        # Create a routine with return_addr=0 (main routine)
+        routine = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x0000,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0x1234],
+            stack=[],
+        )
+        stack_manager.push_routine(routine)
+        zmachine._stackmanager = stack_manager
+
+        writer = QuetzalWriter(zmachine)
+        result = writer._generate_stks_chunk()
+
+        # Expected format with return_pc = 0
+        expected = bytes(
+            [
+                0x00,
+                0x00,
+                0x00,  # return_pc = 0 (main routine)
+                0x01,  # flags (1 local)
+                0x00,  # varnum
+                0x00,  # argflag
+                0x00,
+                0x00,  # eval_stack_size = 0
+                0x12,
+                0x34,  # local_var[0]
+            ]
+        )
+
+        assert result == expected
+
+
+class TestStksRoundTrip:
+    """Test that Stks serialization/deserialization is symmetrical."""
+
+    def test_round_trip_serialization(self):
+        """Test that we can serialize and deserialize frames correctly."""
+        from unittest.mock import Mock
+
+        from mudlib.zmachine.quetzal import QuetzalParser, QuetzalWriter
+        from mudlib.zmachine.zstackmanager import ZRoutine, ZStackManager
+
+        zmachine = Mock()
+        zmachine._mem = Mock()
+        zmachine._mem.version = 5
+
+        # Create original stack with multiple frames
+        original_stack = ZStackManager(zmachine._mem)
+
+        routine1 = ZRoutine(
+            start_addr=0x5000,
+            return_addr=0x1234,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0x0001, 0x0002, 0x0003],
+            stack=[0x1111, 0x2222],
+        )
+        original_stack.push_routine(routine1)
+
+        routine2 = ZRoutine(
+            start_addr=0x6000,
+            return_addr=0x5678,
+            zmem=zmachine._mem,
+            args=[],
+            local_vars=[0xAAAA],
+            stack=[0xBBBB, 0xCCCC, 0xDDDD],
+        )
+        original_stack.push_routine(routine2)
+
+        zmachine._stackmanager = original_stack
+
+        # Serialize
+        writer = QuetzalWriter(zmachine)
+        stks_data = writer._generate_stks_chunk()
+
+        # Deserialize
+        parser = QuetzalParser(zmachine)
+        parser._parse_stks(stks_data)
+
+        # Verify the deserialized stack matches
+        restored_stack = zmachine._stackmanager
+
+        # Should have 2 frames plus the bottom sentinel
+        assert len(restored_stack._call_stack) == 3
+
+        # Check frame 1
+        frame1 = restored_stack._call_stack[1]
+        assert frame1.return_addr == 0x1234
+        assert frame1.local_vars[:3] == [0x0001, 0x0002, 0x0003]
+        assert frame1.stack == [0x1111, 0x2222]
+
+        # Check frame 2
+        frame2 = restored_stack._call_stack[2]
+        assert frame2.return_addr == 0x5678
+        assert frame2.local_vars[:1] == [0xAAAA]
+        assert frame2.stack == [0xBBBB, 0xCCCC, 0xDDDD]

tests/test_zmachine_opcodes.py

@@ -784,8 +784,26 @@ class ZMachineComplexOpcodeTests(TestCase):
         # Should not have branched (test is false)
         self.assertEqual(self.cpu._opdecoder.program_counter, old_pc)
 
-    def test_op_restore_v3_branches_false(self):
+    def test_op_restore_v3_branches_false_when_filesystem_returns_none(self):
-        """Test restore (V3) branches false (no valid save files)."""
+        """Test restore (V3) branches false when filesystem returns None."""
+        from mudlib.zmachine.zmemory import ZMemory
+
+        story = bytearray(1024)
+        story[0] = 3
+        story[0x0E] = 0x04
+        story[0x0F] = 0x00
+
+        zmachine_mock = Mock()
+        zmachine_mock._mem = ZMemory(bytes(story))
+        zmachine_mock._pristine_mem = ZMemory(bytes(story))
+        zmachine_mock._cpu = self.cpu
+        zmachine_mock._stackmanager = self.stack
+
+        self.cpu._zmachine = zmachine_mock
+
+        # Mock filesystem to return None (user cancelled or no file)
+        self.ui.filesystem.restore_game = Mock(return_value=None)
+
         self.decoder.branch_condition = True
         self.decoder.branch_offset = 100
         old_pc = self.cpu._opdecoder.program_counter
@@ -795,6 +813,155 @@ class ZMachineComplexOpcodeTests(TestCase):
         # Should not have branched (test is false)
         self.assertEqual(self.cpu._opdecoder.program_counter, old_pc)
 
+    def test_op_restore_v3_branches_false_when_no_zmachine(self):
+        """Test restore (V3) branches false when zmachine is not set."""
+        self.cpu._zmachine = None
+
+        self.decoder.branch_condition = True
+        self.decoder.branch_offset = 100
+        old_pc = self.cpu._opdecoder.program_counter
+
+        self.cpu.op_restore()
+
+        # Should not have branched (test is false)
+        self.assertEqual(self.cpu._opdecoder.program_counter, old_pc)
+
+    def test_op_restore_v3_branches_true_on_success(self):
+        """Test restore (V3) branches true when restore succeeds."""
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zmemory import ZMemory
+
+        # Create a story with some dynamic memory
+        story = bytearray(1024)
+        story[0] = 3  # version 3
+        story[0x0E] = 0x04  # static memory starts at 0x0400
+        story[0x0F] = 0x00
+        # Set header values
+        story[0x02] = 0x12  # release high byte
+        story[0x03] = 0x34  # release low byte
+        for i, byte in enumerate(b"860509"):
+            story[0x12 + i] = byte
+        story[0x1C] = 0xAB  # checksum high
+        story[0x1D] = 0xCD  # checksum low
+
+        # Create zmachine with modified memory state
+        zmachine_mock = Mock()
+        zmachine_mock._mem = ZMemory(bytes(story))
+        zmachine_mock._pristine_mem = ZMemory(bytes(story))
+        zmachine_mock._cpu = self.cpu
+        zmachine_mock._stackmanager = self.stack
+
+        # Modify some dynamic memory to create a save state
+        zmachine_mock._mem[0x100] = 0x42
+        zmachine_mock._mem[0x200] = 0x99
+
+        self.cpu._zmachine = zmachine_mock
+
+        # Generate save data using QuetzalWriter
+        writer = QuetzalWriter(zmachine_mock)
+        save_data = writer.generate_save_data()
+
+        # Mock filesystem to return the save data
+        self.ui.filesystem.restore_game = Mock(return_value=save_data)
+
+        self.decoder.branch_condition = True
+        self.decoder.branch_offset = 10
+        old_pc = self.cpu._opdecoder.program_counter
+
+        self.cpu.op_restore()
+
+        # Should have branched (test is true)
+        self.assertEqual(self.cpu._opdecoder.program_counter, old_pc + 8)
+
+    def test_op_restore_v3_restores_memory_state(self):
+        """Test restore (V3) correctly restores dynamic memory."""
+        from mudlib.zmachine.quetzal import QuetzalWriter
+        from mudlib.zmachine.zmemory import ZMemory
+
+        # Create a story
+        story = bytearray(1024)
+        story[0] = 3
+        story[0x0E] = 0x04
+        story[0x0F] = 0x00
+        story[0x02] = 0x12
+        story[0x03] = 0x34
+        for i, byte in enumerate(b"860509"):
+            story[0x12 + i] = byte
+        story[0x1C] = 0xAB
+        story[0x1D] = 0xCD
+
+        # Create zmachine with saved state
+        saved_zmachine = Mock()
+        saved_zmachine._mem = ZMemory(bytes(story))
+        saved_zmachine._pristine_mem = ZMemory(bytes(story))
+        saved_zmachine._cpu = self.cpu
+        saved_zmachine._stackmanager = self.stack
+
+        # Modify memory to create unique save state
+        saved_zmachine._mem[0x50] = 0xAA
+        saved_zmachine._mem[0x150] = 0xBB
+        saved_zmachine._mem[0x250] = 0xCC
+
+        # Generate save data
+        writer = QuetzalWriter(saved_zmachine)
+        save_data = writer.generate_save_data()
+
+        # Create fresh zmachine with different state
+        current_zmachine = Mock()
+        current_zmachine._mem = ZMemory(bytes(story))
+        current_zmachine._pristine_mem = ZMemory(bytes(story))
+        current_zmachine._cpu = self.cpu
+        current_zmachine._stackmanager = self.stack
+
+        # Different values in memory
+        current_zmachine._mem[0x50] = 0x11
+        current_zmachine._mem[0x150] = 0x22
+        current_zmachine._mem[0x250] = 0x33
+
+        self.cpu._zmachine = current_zmachine
+
+        # Mock filesystem to return save data
+        self.ui.filesystem.restore_game = Mock(return_value=save_data)
+
+        self.decoder.branch_condition = True
+        self.decoder.branch_offset = 10
+
+        self.cpu.op_restore()
+
+        # Memory should now match saved state
+        self.assertEqual(current_zmachine._mem[0x50], 0xAA)
+        self.assertEqual(current_zmachine._mem[0x150], 0xBB)
+        self.assertEqual(current_zmachine._mem[0x250], 0xCC)
+
+    def test_op_restore_v3_branches_false_on_malformed_data(self):
+        """Test restore (V3) branches false when save data is malformed."""
+        from mudlib.zmachine.zmemory import ZMemory
+
+        story = bytearray(1024)
+        story[0] = 3
+        story[0x0E] = 0x04
+        story[0x0F] = 0x00
+
+        zmachine_mock = Mock()
+        zmachine_mock._mem = ZMemory(bytes(story))
+        zmachine_mock._pristine_mem = ZMemory(bytes(story))
+        zmachine_mock._cpu = self.cpu
+        zmachine_mock._stackmanager = self.stack
+
+        self.cpu._zmachine = zmachine_mock
+
+        # Mock filesystem to return invalid data
+        self.ui.filesystem.restore_game = Mock(return_value=b"invalid data")
+
+        self.decoder.branch_condition = True
+        self.decoder.branch_offset = 10
+        old_pc = self.cpu._opdecoder.program_counter
+
+        self.cpu.op_restore()
+
+        # Should not have branched (test is false)
+        self.assertEqual(self.cpu._opdecoder.program_counter, old_pc)
+
     def test_op_save_v3_branches_true_on_success(self):
         """Test save (V3) branches true when filesystem succeeds."""
         # Create minimal zmachine mock