Fix editor search/replace parsing, dirty flag, and cursor tracking

Integrates the Editor class into the MUD server's shell loop, allowing
players to enter and use the text editor from the game.

Changes:
- Add editor field to Player dataclass
- Modify shell input loop to check player mode and route to editor
- Add edit command to enter editor mode from normal mode
- Use inp (not command.strip()) for editor to preserve indentation
- Show line-numbered prompt in editor mode
- Pop mode and clear editor when done=True
- Add comprehensive integration tests
- Fix test isolation issue in test_movement_updates_position

docs/lessons/charset-vs-mtts.txt

@@ -43,12 +43,26 @@ for MUD clients — they prefer MTTS.
 
 meanwhile, in the same negotiation, tintin++ already told us via MTTS:
 
-    ttype3: MTTS 2825
-        bit 0  (1)    = ANSI color
-        bit 3  (8)    = UTF-8
-        bit 8  (256)  = 256 colors
-        bit 9  (512)  = OSC color palette
-        bit 11 (2048) = true color
+    ttype3: MTTS 2825 = 0b101100001001
+        bit 0  (1)    = ANSI
+        bit 1  (2)    = VT100
+        bit 2  (4)    = UTF-8
+        bit 3  (8)    = 256 COLORS      [SET]
+        bit 4  (16)   = MOUSE TRACKING
+        bit 5  (32)   = OSC COLOR PALETTE
+        bit 6  (64)   = SCREEN READER
+        bit 7  (128)  = PROXY
+        bit 8  (256)  = TRUECOLOR       [SET]
+        bit 9  (512)  = MNES            [SET]
+        bit 10 (1024) = MSLP
+        bit 11 (2048) = SSL             [SET]
+
+    for MTTS 2825: bits 0, 3, 8, 9, 11 are set
+
+NOTE: The original version of this doc had incorrect MTTS bit mappings (copied
+from an unreliable source). This was corrected on 2026-02-07 to match the
+actual MTTS spec from tintin.mudhalla.net/protocols/mtts/. The wrong values
+caused a bug in caps.py that misinterpreted client capabilities.
 
 two protocols, one answer. MTTS (via TTYPE round 3) is what the MUD ecosystem
 uses. RFC 2066 CHARSET is technically correct but practically ignored.

justfile

@@ -6,13 +6,7 @@ typecheck:
     uvx ty check
 
 test:
-    uv run pytest
-
-test-fast:
-    uv run pytest --testmon
-
-test-parallel:
-    uv run pytest -n auto
+    uv run pytest -n auto --testmon
 
 check: lint typecheck test
 

pyproject.toml

@@ -5,6 +5,7 @@ description = "a telnet mud engine"
 requires-python = ">=3.12"
 dependencies = [
     "telnetlib3 @ file:///home/jtm/src/telnetlib3",
+    "pygments>=2.17.0",
 ]
 
 [dependency-groups]

src/mudlib/caps.py

@@ -0,0 +1,90 @@
+"""MTTS (Mud Terminal Type Standard) capability parsing.
+
+Parses MTTS bitfield values from telnetlib3's ttype3 into a structured dataclass.
+MTTS is advertised via TTYPE round 3 as "MTTS <number>" where the number is a
+bitfield of client capabilities.
+
+See docs/lessons/charset-vs-mtts.txt for protocol details.
+"""
+
+from dataclasses import dataclass
+from typing import Literal
+
+
+@dataclass
+class ClientCaps:
+    """Parsed client capabilities from MTTS bitfield."""
+
+    ansi: bool = False
+    vt100: bool = False
+    utf8: bool = False
+    colors_256: bool = False
+    mouse_tracking: bool = False
+    osc_color_palette: bool = False
+    screen_reader: bool = False
+    proxy: bool = False
+    truecolor: bool = False
+    mnes: bool = False
+    mslp: bool = False
+    ssl: bool = False
+
+    @property
+    def color_depth(self) -> Literal["truecolor", "256", "16"]:
+        """Return best available color mode: truecolor, 256, or 16."""
+        if self.truecolor:
+            return "truecolor"
+        if self.colors_256:
+            return "256"
+        return "16"
+
+
+def parse_mtts(ttype3: str | None) -> ClientCaps:
+    """Parse MTTS capability string into ClientCaps dataclass.
+
+    Args:
+        ttype3: String from writer.get_extra_info("ttype3"), e.g., "MTTS 2825"
+
+    Returns:
+        ClientCaps with parsed capabilities. Returns defaults for
+        None/empty/invalid input.
+
+    Bit values from MTTS spec (tintin.mudhalla.net/protocols/mtts/):
+        Bit 0  (1)    = ANSI
+        Bit 1  (2)    = VT100
+        Bit 2  (4)    = UTF-8
+        Bit 3  (8)    = 256 COLORS
+        Bit 4  (16)   = MOUSE TRACKING
+        Bit 5  (32)   = OSC COLOR PALETTE
+        Bit 6  (64)   = SCREEN READER
+        Bit 7  (128)  = PROXY
+        Bit 8  (256)  = TRUECOLOR
+        Bit 9  (512)  = MNES
+        Bit 10 (1024) = MSLP
+        Bit 11 (2048) = SSL
+    """
+    if not ttype3:
+        return ClientCaps()
+
+    parts = ttype3.split()
+    if len(parts) != 2 or parts[0] != "MTTS":
+        return ClientCaps()
+
+    try:
+        value = int(parts[1])
+    except ValueError:
+        return ClientCaps()
+
+    return ClientCaps(
+        ansi=bool(value & 1),
+        vt100=bool(value & 2),
+        utf8=bool(value & 4),
+        colors_256=bool(value & 8),
+        mouse_tracking=bool(value & 16),
+        osc_color_palette=bool(value & 32),
+        screen_reader=bool(value & 64),
+        proxy=bool(value & 128),
+        truecolor=bool(value & 256),
+        mnes=bool(value & 512),
+        mslp=bool(value & 1024),
+        ssl=bool(value & 2048),
+    )

src/mudlib/commands/edit.py

@@ -0,0 +1,29 @@
+"""Edit command for entering the text editor."""
+
+from mudlib.commands import CommandDefinition, register
+from mudlib.editor import Editor
+from mudlib.player import Player
+
+
+async def cmd_edit(player: Player, args: str) -> None:
+    """Enter the text editor.
+
+    Args:
+        player: The player executing the command
+        args: Command arguments (unused for now)
+    """
+
+    async def save_callback(content: str) -> None:
+        await player.send("Content saved.\r\n")
+
+    player.editor = Editor(
+        save_callback=save_callback,
+        content_type="text",
+        color_depth=player.color_depth,
+    )
+    player.mode_stack.append("editor")
+    await player.send("Entering editor. Type :h for help.\r\n")
+
+
+# Register the edit command
+register(CommandDefinition("edit", cmd_edit, mode="normal"))

src/mudlib/commands/look.py

@@ -64,10 +64,10 @@ async def cmd_look(player: Player, args: str) -> None:
         for x, tile in enumerate(row):
             # Check if this is the player's position
             if x == center_x and y == center_y:
-                line.append(colorize_terrain("@"))
+                line.append(colorize_terrain("@", player.color_depth))
             # Check if this is another player's position
             elif (x, y) in other_player_positions:
-                line.append(colorize_terrain("*"))
+                line.append(colorize_terrain("*", player.color_depth))
             else:
                 # Check for active effects at this world position
                 world_x, world_y = world.wrap(
@@ -80,7 +80,7 @@ async def cmd_look(player: Player, args: str) -> None:
                     e = effects[-1]
                     line.append(f"{e.color}{e.char}{RESET}")
                 else:
-                    line.append(colorize_terrain(tile))
+                    line.append(colorize_terrain(tile, player.color_depth))
         output_lines.append("".join(line))
 
     # Send to player

src/mudlib/editor.py

@@ -0,0 +1,403 @@
+"""Text editor for in-game content editing."""
+
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass, field
+
+from mudlib.render.highlight import highlight
+
+
+@dataclass
+class EditorResponse:
+    """Response from editor input handling."""
+
+    output: str  # text to send back to the player
+    done: bool  # True if editor should be closed (quit/save-and-quit)
+    saved: bool = False  # True if save was performed
+
+
+@dataclass
+class Editor:
+    """Line-based text editor for in-game content.
+
+    Doesn't know about telnet — takes string input, returns string output.
+    Will be integrated into the shell loop in a later step.
+    """
+
+    buffer: list[str] = field(default_factory=list)
+    cursor: int = 0  # current line (0-indexed internally)
+    undo_stack: list[list[str]] = field(default_factory=list)
+    save_callback: Callable[[str], Awaitable[None]] | None = None
+    content_type: str = "text"  # hint for syntax highlighting later
+    color_depth: str = "16"  # "16", "256", or "truecolor"
+    dirty: bool = False
+
+    def __init__(
+        self,
+        initial_content: str = "",
+        save_callback: Callable[[str], Awaitable[None]] | None = None,
+        content_type: str = "text",
+        color_depth: str = "16",
+    ):
+        """Initialize editor with optional content."""
+        self.save_callback = save_callback
+        self.content_type = content_type
+        self.color_depth = color_depth
+        self.cursor = 0
+        self.undo_stack = []
+        self.dirty = False
+
+        if initial_content:
+            self.buffer = initial_content.split("\n")
+        else:
+            self.buffer = []
+
+    def _save_undo_state(self) -> None:
+        """Save current buffer state to undo stack."""
+        self.undo_stack.append(self.buffer.copy())
+        # Cap undo stack at 50 entries
+        if len(self.undo_stack) > 50:
+            self.undo_stack.pop(0)
+
+    def _mark_dirty(self) -> None:
+        """Mark buffer as modified."""
+        self.dirty = True
+
+    def _view_buffer(self) -> str:
+        """Return formatted view of entire buffer."""
+        if not self.buffer:
+            return "(empty buffer)"
+
+        # Use syntax highlighting if content_type is not "text"
+        if self.content_type != "text":
+            content = "\n".join(self.buffer)
+            highlighted = highlight(
+                content,
+                language=self.content_type,
+                color_depth=self.color_depth,
+                line_numbers=True,
+            )
+            # If highlight() returned the original (unknown language), fall through
+            if "\033[" in highlighted:
+                return highlighted
+
+        # Fall back to plain line-number formatting
+        max_line_num = len(self.buffer)
+        padding = len(str(max_line_num))
+
+        lines = []
+        for i, line in enumerate(self.buffer, 1):
+            lines.append(f"{i:>{padding}}  {line}")
+        return "\n".join(lines)
+
+    def _view_line(self, line_num: int) -> str:
+        """Return formatted view of specific line with context."""
+        if line_num < 1 or line_num > len(self.buffer):
+            return f"Error: Line {line_num} does not exist"
+
+        # Show 3 lines of context on each side
+        context = 3
+        start = max(0, line_num - 1 - context)
+        end = min(len(self.buffer), line_num + context)
+
+        # Use syntax highlighting if content_type is not "text"
+        if self.content_type != "text":
+            # Get the context window
+            context_lines = self.buffer[start:end]
+            content = "\n".join(context_lines)
+            highlighted = highlight(
+                content,
+                language=self.content_type,
+                color_depth=self.color_depth,
+                line_numbers=True,
+            )
+            # If highlight() returned highlighted content, use it
+            if "\033[" in highlighted:
+                return highlighted
+
+        # Fall back to plain line-number formatting
+        max_line_num = end
+        padding = len(str(max_line_num))
+
+        lines = []
+        for i in range(start, end):
+            display_num = i + 1
+            lines.append(f"{display_num:>{padding}}  {self.buffer[i]}")
+        return "\n".join(lines)
+
+    def _insert_line(self, line_num: int, text: str) -> str:
+        """Insert text at specified line number."""
+        if line_num < 1:
+            return "Error: Line number must be >= 1"
+
+        self._save_undo_state()
+
+        # Insert at end if line_num is beyond buffer
+        if line_num > len(self.buffer):
+            self.buffer.append(text)
+            self.cursor = len(self.buffer) - 1
+        else:
+            self.buffer.insert(line_num - 1, text)
+            self.cursor = line_num - 1
+
+        self._mark_dirty()
+        return f"Inserted at line {line_num}"
+
+    def _delete_line(self, start: int, end: int | None = None) -> str:
+        """Delete line(s) at specified range."""
+        if start < 1 or start > len(self.buffer):
+            return f"Error: Line {start} does not exist"
+
+        self._save_undo_state()
+
+        if end is None:
+            # Delete single line
+            self.buffer.pop(start - 1)
+            self.cursor = min(start - 1, len(self.buffer) - 1)
+            self._mark_dirty()
+            return f"Deleted line {start}"
+        else:
+            # Delete range
+            if end < start or end > len(self.buffer):
+                return f"Error: Invalid range {start}-{end}"
+
+            # Delete from start to end (inclusive)
+            del self.buffer[start - 1 : end]
+            self.cursor = min(start - 1, len(self.buffer) - 1)
+            self._mark_dirty()
+            return f"Deleted lines {start}-{end}"
+
+    def _replace_line(self, line_num: int, text: str) -> str:
+        """Replace line at specified number with new text."""
+        if line_num < 1 or line_num > len(self.buffer):
+            return f"Error: Line {line_num} does not exist"
+
+        self._save_undo_state()
+        self.buffer[line_num - 1] = text
+        self._mark_dirty()
+        return f"Replaced line {line_num}"
+
+    def _search_replace(self, old: str, new: str, replace_all: bool = False) -> str:
+        """Search and replace text in buffer."""
+        self._save_undo_state()
+        count = 0
+
+        for i, line in enumerate(self.buffer):
+            if old in line:
+                if replace_all:
+                    self.buffer[i] = line.replace(old, new)
+                    count += line.count(old)
+                else:
+                    self.buffer[i] = line.replace(old, new, 1)
+                    count = 1
+                    self._mark_dirty()
+                    return f"Replaced '{old}' with '{new}' on line {i + 1}"
+
+        if count > 0:
+            self._mark_dirty()
+            return f"Replaced {count} occurrence(s) of '{old}' with '{new}'"
+        else:
+            # Restore undo state since nothing changed
+            self.undo_stack.pop()
+            return f"Not found: '{old}'"
+
+    def _undo(self) -> str:
+        """Undo last buffer change."""
+        if not self.undo_stack:
+            return "Nothing to undo"
+
+        self.buffer = self.undo_stack.pop()
+        # Conservative approach: if we undid something, the buffer is now different
+        # from what was saved (even if we undo past a save point)
+        self.dirty = True
+        # Reset cursor to end of buffer after undo
+        self.cursor = len(self.buffer) - 1 if self.buffer else 0
+        return "Undone last change"
+
+    async def _save(self) -> str:
+        """Save buffer content via callback."""
+        if self.save_callback is None:
+            return "Error: Cannot save (no save callback configured)"
+
+        content = "\n".join(self.buffer)
+        await self.save_callback(content)
+        self.dirty = False
+        return "Saved"
+
+    def _help(self) -> str:
+        """Return help text."""
+        return """Editor Commands:
+:           - view entire buffer with line numbers
+:N          - view line N with context
+:h          - show this help
+:i N text   - insert 'text' at line N
+:d N        - delete line N
+:d N M      - delete lines N through M
+:r N text   - replace line N with 'text'
+:s old new  - search and replace first occurrence
+:sa old new - search and replace all occurrences
+:w          - save
+:wq         - save and quit
+:q          - quit (warns if unsaved changes)
+:q!         - force quit without saving
+:u          - undo last change
+.           - save and quit (MOO convention)
+
+Any line not starting with : is appended to the buffer."""
+
+    async def handle_input(self, line: str) -> EditorResponse:
+        """Handle editor input and return response."""
+        # Special case: dot on its own saves and quits
+        if line == ".":
+            if self.save_callback is None:
+                return EditorResponse(
+                    output="Error: Cannot save (no save callback configured)",
+                    done=False,
+                )
+            save_msg = await self._save()
+            return EditorResponse(output=save_msg, done=True, saved=True)
+
+        # Check if it's a command
+        if not line.startswith(":"):
+            # Append to buffer
+            self._save_undo_state()
+            self.buffer.append(line)
+            self.cursor = len(self.buffer) - 1
+            self._mark_dirty()
+            return EditorResponse(output="", done=False)
+
+        # Parse command
+        cmd = line[1:].strip()
+
+        # Empty command - view buffer
+        if not cmd:
+            output = self._view_buffer()
+            return EditorResponse(output=output, done=False)
+
+        # Check for numeric line view
+        if cmd.isdigit():
+            line_num = int(cmd)
+            output = self._view_line(line_num)
+            return EditorResponse(output=output, done=False)
+
+        # Parse command parts
+        parts = cmd.split(None, 1)
+        command = parts[0]
+        args = parts[1] if len(parts) > 1 else ""
+
+        # Help
+        if command == "h":
+            output = self._help()
+            return EditorResponse(output=output, done=False)
+
+        # Insert
+        if command == "i":
+            if not args:
+                return EditorResponse(
+                    output="Error: :i requires line number and text", done=False
+                )
+            parts = args.split(None, 1)
+            if len(parts) < 2:
+                return EditorResponse(
+                    output="Error: :i requires line number and text", done=False
+                )
+            try:
+                line_num = int(parts[0])
+                text = parts[1]
+                output = self._insert_line(line_num, text)
+                return EditorResponse(output=output, done=False)
+            except ValueError:
+                return EditorResponse(output="Error: Invalid line number", done=False)
+
+        # Delete
+        if command == "d":
+            if not args:
+                return EditorResponse(
+                    output="Error: :d requires line number(s)", done=False
+                )
+            parts = args.split()
+            try:
+                start = int(parts[0])
+                end = int(parts[1]) if len(parts) > 1 else None
+                output = self._delete_line(start, end)
+                return EditorResponse(output=output, done=False)
+            except (ValueError, IndexError):
+                return EditorResponse(
+                    output="Error: Invalid line number(s)", done=False
+                )
+
+        # Replace
+        if command == "r":
+            if not args:
+                return EditorResponse(
+                    output="Error: :r requires line number and text", done=False
+                )
+            parts = args.split(None, 1)
+            if len(parts) < 2:
+                return EditorResponse(
+                    output="Error: :r requires line number and text", done=False
+                )
+            try:
+                line_num = int(parts[0])
+                text = parts[1]
+                output = self._replace_line(line_num, text)
+                return EditorResponse(output=output, done=False)
+            except ValueError:
+                return EditorResponse(output="Error: Invalid line number", done=False)
+
+        # Search and replace
+        if command == "s":
+            split_args = args.split(None, 1)
+            if len(split_args) < 2:
+                return EditorResponse(
+                    output="Error: :s requires old and new text", done=False
+                )
+            old = split_args[0]
+            new = split_args[1]
+            output = self._search_replace(old, new, replace_all=False)
+            return EditorResponse(output=output, done=False)
+
+        # Search and replace all
+        if command == "sa":
+            parts = args.split(None, 1)
+            if len(parts) < 2:
+                return EditorResponse(
+                    output="Error: :sa requires old and new text", done=False
+                )
+            old = parts[0]
+            new = parts[1]
+            output = self._search_replace(old, new, replace_all=True)
+            return EditorResponse(output=output, done=False)
+
+        # Undo
+        if command == "u":
+            output = self._undo()
+            return EditorResponse(output=output, done=False)
+
+        # Save
+        if command == "w":
+            output = await self._save()
+            return EditorResponse(output=output, done=False, saved=True)
+
+        # Save and quit
+        if command == "wq":
+            output = await self._save()
+            return EditorResponse(output=output, done=True, saved=True)
+
+        # Quit
+        if command == "q":
+            if self.dirty:
+                return EditorResponse(
+                    output=(
+                        "Unsaved changes! Use :wq to save and quit, "
+                        "or :q! to force quit"
+                    ),
+                    done=False,
+                )
+            return EditorResponse(output="", done=True)
+
+        # Force quit
+        if command == "q!":
+            return EditorResponse(output="", done=True)
+
+        # Unknown command
+        return EditorResponse(output=f"Unknown command: :{command}", done=False)

src/mudlib/player.py

@@ -1,10 +1,16 @@
 """Player state and registry."""
 
-from dataclasses import dataclass, field
-from typing import Any
+from __future__ import annotations
 
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Any
+
+from mudlib.caps import ClientCaps
 from mudlib.entity import Entity
 
+if TYPE_CHECKING:
+    from mudlib.editor import Editor
+
 
 @dataclass
 class Player(Entity):
@@ -14,12 +20,19 @@ class Player(Entity):
     reader: Any = None  # telnetlib3 TelnetReader for reading input
     flying: bool = False
     mode_stack: list[str] = field(default_factory=lambda: ["normal"])
+    caps: ClientCaps = field(default_factory=lambda: ClientCaps(ansi=True))
+    editor: Editor | None = None
 
     @property
     def mode(self) -> str:
         """Current mode is the top of the stack."""
         return self.mode_stack[-1]
 
+    @property
+    def color_depth(self) -> str:
+        """Best available color mode: truecolor, 256, or 16."""
+        return self.caps.color_depth
+
     async def send(self, message: str) -> None:
         """Send a message to the player via their telnet writer."""
         self.writer.write(message)

src/mudlib/render/ansi.py

@@ -24,7 +24,68 @@ BRIGHT_MAGENTA = "\033[95m"
 BRIGHT_CYAN = "\033[96m"
 BRIGHT_WHITE = "\033[97m"
 
-# terrain color mapping
+
+def fg_256(n: int) -> str:
+    """Generate 256-color foreground escape code.
+
+    Args:
+        n: Color index (0-255). Values outside range are clamped.
+
+    Returns:
+        ANSI escape sequence for 256-color foreground.
+    """
+    clamped = max(0, min(255, n))
+    return f"\033[38;5;{clamped}m"
+
+
+def bg_256(n: int) -> str:
+    """Generate 256-color background escape code.
+
+    Args:
+        n: Color index (0-255). Values outside range are clamped.
+
+    Returns:
+        ANSI escape sequence for 256-color background.
+    """
+    clamped = max(0, min(255, n))
+    return f"\033[48;5;{clamped}m"
+
+
+def fg_rgb(r: int, g: int, b: int) -> str:
+    """Generate truecolor foreground escape code.
+
+    Args:
+        r: Red component (0-255). Values outside range are clamped.
+        g: Green component (0-255). Values outside range are clamped.
+        b: Blue component (0-255). Values outside range are clamped.
+
+    Returns:
+        ANSI escape sequence for truecolor foreground.
+    """
+    r_clamped = max(0, min(255, r))
+    g_clamped = max(0, min(255, g))
+    b_clamped = max(0, min(255, b))
+    return f"\033[38;2;{r_clamped};{g_clamped};{b_clamped}m"
+
+
+def bg_rgb(r: int, g: int, b: int) -> str:
+    """Generate truecolor background escape code.
+
+    Args:
+        r: Red component (0-255). Values outside range are clamped.
+        g: Green component (0-255). Values outside range are clamped.
+        b: Blue component (0-255). Values outside range are clamped.
+
+    Returns:
+        ANSI escape sequence for truecolor background.
+    """
+    r_clamped = max(0, min(255, r))
+    g_clamped = max(0, min(255, g))
+    b_clamped = max(0, min(255, b))
+    return f"\033[48;2;{r_clamped};{g_clamped};{b_clamped}m"
+
+
+# terrain color mapping (16-color baseline)
 TERRAIN_COLORS = {
     ".": GREEN,  # grass
     "^": BRIGHT_BLACK,  # mountain
@@ -35,19 +96,63 @@ TERRAIN_COLORS = {
     "*": BOLD + BRIGHT_RED,  # other entity
 }
 
+# 256-color terrain palette
+TERRAIN_COLORS_256 = {
+    ".": fg_256(34),  # grass - richer green
+    "^": fg_256(242),  # mountain - gray
+    "~": fg_256(27),  # water - deeper blue
+    "T": fg_256(22),  # forest - darker green
+    ":": fg_256(221),  # sand - warm yellow
+    "@": BOLD + fg_256(231),  # player - bright white
+    "*": BOLD + fg_256(196),  # other entity - bright red
+}
+
+# truecolor terrain palette
+TERRAIN_COLORS_RGB = {
+    ".": fg_rgb(76, 175, 80),  # grass - material green
+    "^": fg_rgb(96, 125, 139),  # mountain - blue-gray
+    "~": fg_rgb(33, 150, 243),  # water - material blue
+    "T": fg_rgb(27, 94, 32),  # forest - dark green
+    ":": fg_rgb(255, 235, 59),  # sand - bright yellow
+    "@": BOLD + fg_rgb(255, 255, 255),  # player - pure white
+    "*": BOLD + fg_rgb(244, 67, 54),  # other entity - material red
+}
+
+
+def colorize_terrain(char: str, color_depth: str = "16") -> str:
+    """Return ANSI-colored version of terrain character.
+
+    Args:
+        char: Terrain character to colorize
+        color_depth: Color mode - "16", "256", or "truecolor"
+
+    Returns:
+        ANSI-colored character with reset code, or unchanged char if no color mapping.
+    """
+    if color_depth == "truecolor":
+        color = TERRAIN_COLORS_RGB.get(char, "")
+    elif color_depth == "256":
+        color = TERRAIN_COLORS_256.get(char, "")
+    else:
+        color = TERRAIN_COLORS.get(char, "")
 
-def colorize_terrain(char: str) -> str:
-    """Return ANSI-colored version of terrain character."""
-    color = TERRAIN_COLORS.get(char, "")
     if color:
         return f"{color}{char}{RESET}"
     return char
 
 
-def colorize_map(grid: list[list[str]]) -> str:
-    """Colorize a 2D grid of terrain and return as string."""
+def colorize_map(grid: list[list[str]], color_depth: str = "16") -> str:
+    """Colorize a 2D grid of terrain and return as string.
+
+    Args:
+        grid: 2D list of terrain characters
+        color_depth: Color mode - "16", "256", or "truecolor"
+
+    Returns:
+        Newline-separated string of colorized terrain rows.
+    """
     lines = []
     for row in grid:
-        colored_row = "".join(colorize_terrain(char) for char in row)
+        colored_row = "".join(colorize_terrain(char, color_depth) for char in row)
         lines.append(colored_row)
     return "\n".join(lines)

src/mudlib/render/highlight.py

@@ -0,0 +1,78 @@
+"""Syntax highlighting using Pygments with ANSI color depth awareness."""
+
+from pygments import highlight as pygments_highlight
+from pygments.formatters.terminal import TerminalFormatter
+from pygments.formatters.terminal256 import Terminal256Formatter
+from pygments.lexers import get_lexer_by_name
+from pygments.util import ClassNotFound
+
+
+def highlight(
+    code: str,
+    language: str = "python",
+    color_depth: str = "16",
+    line_numbers: bool = False,
+) -> str:
+    """Highlight code with syntax coloring appropriate for client's terminal.
+
+    Args:
+        code: Source code to highlight
+        language: Language name (python, toml, etc.)
+        color_depth: Client color capability ("truecolor", "256", or "16")
+        line_numbers: Whether to prefix lines with line numbers
+
+    Returns:
+        ANSI-colored code string, or original code if language is unknown.
+        Trailing newlines are stripped for clean telnet display.
+    """
+    if not code:
+        return ""
+
+    # Try to get the appropriate lexer
+    try:
+        lexer = get_lexer_by_name(language)
+    except ClassNotFound:
+        # Unknown language, return original text
+        return code
+
+    # Choose formatter based on color depth
+    # Use 256-color formatter for both "256" and "truecolor"
+    # Pygments doesn't have a true truecolor formatter, 256 is the best we have
+    formatter = TerminalFormatter() if color_depth == "16" else Terminal256Formatter()
+
+    # Apply syntax highlighting
+    result = pygments_highlight(code, lexer, formatter)
+
+    # Strip trailing newline that Pygments adds
+    if result.endswith("\n"):
+        result = result[:-1]
+
+    # Add line numbers if requested
+    if line_numbers:
+        result = _add_line_numbers(result)
+
+    return result
+
+
+def _add_line_numbers(highlighted_code: str) -> str:
+    """Add line numbers to highlighted code using ANSI dim styling.
+
+    Args:
+        highlighted_code: ANSI-colored code string
+
+    Returns:
+        Code with line numbers prefixed to each line
+    """
+    lines = highlighted_code.split("\n")
+    numbered_lines = []
+
+    # ANSI dim styling for line numbers
+    dim = "\033[2m"
+    reset = "\033[0m"
+
+    for i, line in enumerate(lines, start=1):
+        # Format: dim line number, reset, then the code
+        numbered_line = f"{dim}{i:3d}{reset} {line}"
+        numbered_lines.append(numbered_line)
+
+    return "\n".join(numbered_lines)

src/mudlib/server.py

@@ -11,10 +11,12 @@ import telnetlib3
 from telnetlib3.server_shell import readline2
 
 import mudlib.commands
+import mudlib.commands.edit
 import mudlib.commands.fly
 import mudlib.commands.look
 import mudlib.commands.movement
 import mudlib.commands.quit
+from mudlib.caps import parse_mtts
 from mudlib.combat.commands import register_combat_commands
 from mudlib.combat.engine import process_combat
 from mudlib.content import load_commands
@@ -267,6 +269,16 @@ async def shell(
         reader=_reader,
     )
 
+    # Parse and store client capabilities from MTTS
+    ttype3 = _writer.get_extra_info("ttype3")
+    player.caps = parse_mtts(ttype3)
+    log.debug(
+        "%s capabilities: %s (color_depth=%s)",
+        player_name,
+        player.caps,
+        player.color_depth,
+    )
+
     # Register player
     players[player_name] = player
     log.info(
@@ -286,7 +298,11 @@ async def shell(
     # Command loop
     try:
         while not _writer.is_closing():
-            _writer.write("mud> ")
+            # Show appropriate prompt based on mode
+            if player.mode == "editor" and player.editor:
+                _writer.write(f"  {player.editor.cursor + 1}> ")
+            else:
+                _writer.write("mud> ")
             await _writer.drain()
 
             inp = await readline2(_reader, _writer)
@@ -294,11 +310,20 @@ async def shell(
                 break
 
             command = inp.strip()
-            if not command:
+            if not command and player.mode != "editor":
                 continue
 
-            # Dispatch command
-            await mudlib.commands.dispatch(player, command)
+            # Handle editor mode
+            if player.mode == "editor" and player.editor:
+                response = await player.editor.handle_input(inp)
+                if response.output:
+                    await player.send(response.output)
+                if response.done:
+                    player.editor = None
+                    player.mode_stack.pop()
+            else:
+                # Dispatch normal command
+                await mudlib.commands.dispatch(player, command)
 
             # Check if writer was closed by quit command
             if _writer.is_closing():

tests/test_ansi.py

@@ -1,4 +1,12 @@
-from mudlib.render.ansi import RESET, colorize_map, colorize_terrain
+from mudlib.render.ansi import (
+    RESET,
+    bg_256,
+    bg_rgb,
+    colorize_map,
+    colorize_terrain,
+    fg_256,
+    fg_rgb,
+)
 
 
 def test_colorize_terrain_grass():
@@ -45,3 +53,109 @@ def test_colorize_map():
 
     # should have ANSI codes
     assert "\033[" in result
+
+
+def test_fg_256_basic():
+    """Generate 256-color foreground code."""
+    assert fg_256(0) == "\033[38;5;0m"
+    assert fg_256(15) == "\033[38;5;15m"
+    assert fg_256(42) == "\033[38;5;42m"
+    assert fg_256(255) == "\033[38;5;255m"
+
+
+def test_bg_256_basic():
+    """Generate 256-color background code."""
+    assert bg_256(0) == "\033[48;5;0m"
+    assert bg_256(15) == "\033[48;5;15m"
+    assert bg_256(42) == "\033[48;5;42m"
+    assert bg_256(255) == "\033[48;5;255m"
+
+
+def test_fg_256_clamping():
+    """Clamp 256-color values to valid range (0-255)."""
+    assert fg_256(-1) == "\033[38;5;0m"
+    assert fg_256(256) == "\033[38;5;255m"
+    assert fg_256(999) == "\033[38;5;255m"
+
+
+def test_bg_256_clamping():
+    """Clamp 256-color values to valid range (0-255)."""
+    assert bg_256(-1) == "\033[48;5;0m"
+    assert bg_256(256) == "\033[48;5;255m"
+    assert bg_256(999) == "\033[48;5;255m"
+
+
+def test_fg_rgb_basic():
+    """Generate truecolor foreground code."""
+    assert fg_rgb(0, 0, 0) == "\033[38;2;0;0;0m"
+    assert fg_rgb(255, 255, 255) == "\033[38;2;255;255;255m"
+    assert fg_rgb(128, 64, 192) == "\033[38;2;128;64;192m"
+
+
+def test_bg_rgb_basic():
+    """Generate truecolor background code."""
+    assert bg_rgb(0, 0, 0) == "\033[48;2;0;0;0m"
+    assert bg_rgb(255, 255, 255) == "\033[48;2;255;255;255m"
+    assert bg_rgb(128, 64, 192) == "\033[48;2;128;64;192m"
+
+
+def test_fg_rgb_clamping():
+    """Clamp RGB values to valid range (0-255)."""
+    assert fg_rgb(-1, 0, 0) == "\033[38;2;0;0;0m"
+    assert fg_rgb(0, 300, 0) == "\033[38;2;0;255;0m"
+    assert fg_rgb(0, 0, 999) == "\033[38;2;0;0;255m"
+    assert fg_rgb(-10, 300, 500) == "\033[38;2;0;255;255m"
+
+
+def test_bg_rgb_clamping():
+    """Clamp RGB values to valid range (0-255)."""
+    assert bg_rgb(-1, 0, 0) == "\033[48;2;0;0;0m"
+    assert bg_rgb(0, 300, 0) == "\033[48;2;0;255;0m"
+    assert bg_rgb(0, 0, 999) == "\033[48;2;0;0;255m"
+    assert bg_rgb(-10, 300, 500) == "\033[48;2;0;255;255m"
+
+
+def test_colorize_terrain_default_16color():
+    """Default color_depth uses 16-color palette."""
+    result = colorize_terrain(".")
+    assert "\033[32m" in result  # GREEN
+    assert "." in result
+    assert RESET in result
+
+
+def test_colorize_terrain_256color():
+    """color_depth=256 uses 256-color palette."""
+    result = colorize_terrain(".", "256")
+    assert "\033[38;5;" in result  # 256-color code
+    assert "." in result
+    assert RESET in result
+
+
+def test_colorize_terrain_truecolor():
+    """color_depth=truecolor uses RGB palette."""
+    result = colorize_terrain(".", "truecolor")
+    assert "\033[38;2;" in result  # truecolor code
+    assert "." in result
+    assert RESET in result
+
+
+def test_colorize_map_default_16color():
+    """colorize_map with default uses 16-color palette."""
+    grid = [[".", "~"], ["^", "T"]]
+    result = colorize_map(grid)
+    assert "\033[32m" in result  # GREEN for grass
+    assert "\033[34m" in result  # BLUE for water
+
+
+def test_colorize_map_256color():
+    """colorize_map with color_depth=256 uses 256-color palette."""
+    grid = [[".", "~"]]
+    result = colorize_map(grid, "256")
+    assert "\033[38;5;" in result  # 256-color codes present
+
+
+def test_colorize_map_truecolor():
+    """colorize_map with color_depth=truecolor uses RGB palette."""
+    grid = [[".", "~"]]
+    result = colorize_map(grid, "truecolor")
+    assert "\033[38;2;" in result  # truecolor codes present

tests/test_caps.py

@@ -0,0 +1,117 @@
+"""Tests for MTTS capability parsing."""
+
+from mudlib.caps import parse_mtts
+
+
+def test_parse_mtts_tintin():
+    """Parse tintin++ MTTS 2825 correctly.
+
+    2825 in binary = 0b101100001001
+    Bits set: 0, 3, 8, 9, 11
+    = ANSI(1) + 256colors(8) + truecolor(256) + MNES(512) + SSL(2048)
+    """
+    caps = parse_mtts("MTTS 2825")
+    assert caps.ansi is True
+    assert caps.vt100 is False
+    assert caps.utf8 is False
+    assert caps.colors_256 is True
+    assert caps.mouse_tracking is False
+    assert caps.osc_color_palette is False
+    assert caps.screen_reader is False
+    assert caps.proxy is False
+    assert caps.truecolor is True
+    assert caps.mnes is True
+    assert caps.mslp is False
+    assert caps.ssl is True
+    assert caps.color_depth == "truecolor"
+
+
+def test_parse_mtts_basic():
+    """Parse MTTS 137 (ANSI + 256colors + proxy)."""
+    # 137 = 1 (ANSI) + 8 (256colors) + 128 (proxy)
+    caps = parse_mtts("MTTS 137")
+    assert caps.ansi is True
+    assert caps.utf8 is False
+    assert caps.colors_256 is True
+    assert caps.proxy is True
+    assert caps.truecolor is False
+    assert caps.color_depth == "256"
+
+
+def test_parse_mtts_zero():
+    """Parse MTTS 0 (nothing supported)."""
+    caps = parse_mtts("MTTS 0")
+    assert caps.ansi is False
+    assert caps.utf8 is False
+    assert caps.colors_256 is False
+    assert caps.truecolor is False
+    assert caps.color_depth == "16"
+
+
+def test_parse_mtts_256_colors_only():
+    """Parse MTTS with JUST 256 colors (no truecolor)."""
+    # 9 = 1 (ANSI) + 8 (256colors)
+    caps = parse_mtts("MTTS 9")
+    assert caps.ansi is True
+    assert caps.utf8 is False
+    assert caps.colors_256 is True
+    assert caps.truecolor is False
+    assert caps.color_depth == "256"
+
+
+def test_parse_mtts_utf8_no_colors():
+    """Parse MTTS with UTF-8 but no extended colors."""
+    # 5 = 1 (ANSI) + 4 (UTF-8)
+    caps = parse_mtts("MTTS 5")
+    assert caps.ansi is True
+    assert caps.utf8 is True
+    assert caps.colors_256 is False
+    assert caps.truecolor is False
+    assert caps.color_depth == "16"
+
+
+def test_parse_mtts_empty():
+    """Handle empty string gracefully."""
+    caps = parse_mtts("")
+    assert caps.ansi is False
+    assert caps.utf8 is False
+    assert caps.color_depth == "16"
+
+
+def test_parse_mtts_none():
+    """Handle None gracefully."""
+    caps = parse_mtts(None)
+    assert caps.ansi is False
+    assert caps.utf8 is False
+    assert caps.color_depth == "16"
+
+
+def test_parse_mtts_non_mtts():
+    """Handle non-MTTS ttype3 strings (e.g., UNKNOWN-TERMINAL)."""
+    caps = parse_mtts("UNKNOWN-TERMINAL")
+    assert caps.ansi is False
+    assert caps.utf8 is False
+    assert caps.color_depth == "16"
+
+
+def test_parse_mtts_malformed():
+    """Handle malformed MTTS strings."""
+    caps = parse_mtts("MTTS")
+    assert caps.ansi is False
+    assert caps.utf8 is False
+    assert caps.color_depth == "16"
+
+
+def test_color_depth_priority():
+    """Verify color_depth returns best available mode."""
+    # truecolor wins
+    caps = parse_mtts("MTTS 2825")
+    assert caps.color_depth == "truecolor"
+
+    # 256 wins over 16
+    caps = parse_mtts("MTTS 9")
+    assert caps.color_depth == "256"
+
+    # fallback to 16
+    caps = parse_mtts("MTTS 5")  # 1 (ANSI) + 4 (UTF-8)
+    assert caps.color_depth == "16"

tests/test_commands.py

@@ -138,6 +138,11 @@ async def test_movement_updates_position(player, mock_world):
     movement.world = mock_world
     look.world = mock_world
 
+    # Clear players registry to avoid test pollution
+    from mudlib.player import players
+
+    players.clear()
+
     original_x, original_y = player.x, player.y
     await movement.move_north(player, "")
 

tests/test_editor.py

@@ -0,0 +1,436 @@
+"""Tests for the text editor."""
+
+import pytest
+
+from mudlib.editor import Editor
+
+
+@pytest.mark.asyncio
+async def test_create_editor_with_empty_buffer():
+    """Editor starts with empty buffer."""
+    editor = Editor()
+    assert editor.buffer == []
+    assert editor.cursor == 0
+    assert editor.dirty is False
+
+
+@pytest.mark.asyncio
+async def test_create_editor_with_initial_content():
+    """Editor can be initialized with content."""
+    editor = Editor(initial_content="line 1\nline 2\nline 3")
+    assert editor.buffer == ["line 1", "line 2", "line 3"]
+    assert editor.dirty is False
+
+
+@pytest.mark.asyncio
+async def test_append_line():
+    """Typing text that isn't a command appends to buffer."""
+    editor = Editor()
+    response = await editor.handle_input("hello world")
+    assert response.output == ""
+    assert response.done is False
+    assert editor.buffer == ["hello world"]
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_append_multiple_lines():
+    """Multiple lines can be appended."""
+    editor = Editor()
+    await editor.handle_input("line 1")
+    await editor.handle_input("line 2")
+    await editor.handle_input("line 3")
+    assert editor.buffer == ["line 1", "line 2", "line 3"]
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_view_buffer():
+    """':' shows the entire buffer with line numbers."""
+    editor = Editor(initial_content="line 1\nline 2\nline 3")
+    response = await editor.handle_input(":")
+    assert "1  line 1" in response.output
+    assert "2  line 2" in response.output
+    assert "3  line 3" in response.output
+
+
+@pytest.mark.asyncio
+async def test_view_empty_buffer():
+    """':' on empty buffer shows appropriate message."""
+    editor = Editor()
+    response = await editor.handle_input(":")
+    assert "empty" in response.output.lower() or response.output == ""
+
+
+@pytest.mark.asyncio
+async def test_view_specific_line():
+    """':5' shows line 5 with context."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 11)]))
+    response = await editor.handle_input(":5")
+    # Should show lines 2-8 (3 lines of context on each side)
+    assert "5  line 5" in response.output
+    assert "2  line 2" in response.output
+    assert "8  line 8" in response.output
+
+
+@pytest.mark.asyncio
+async def test_view_specific_line_at_start():
+    """Viewing line near start shows available context."""
+    editor = Editor(initial_content="line 1\nline 2\nline 3")
+    response = await editor.handle_input(":1")
+    assert "1  line 1" in response.output
+
+
+@pytest.mark.asyncio
+async def test_insert_at_line():
+    """':i 5 text' inserts 'text' at line 5."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 6)]))
+    await editor.handle_input(":i 3 inserted text")
+    assert editor.buffer[2] == "inserted text"
+    assert editor.buffer[3] == "line 3"
+    assert len(editor.buffer) == 6
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_insert_at_end():
+    """':i' can insert at end of buffer."""
+    editor = Editor(initial_content="line 1\nline 2")
+    await editor.handle_input(":i 3 line 3")
+    assert editor.buffer[2] == "line 3"
+
+
+@pytest.mark.asyncio
+async def test_delete_single_line():
+    """':d 5' deletes line 5."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 6)]))
+    await editor.handle_input(":d 3")
+    assert editor.buffer == ["line 1", "line 2", "line 4", "line 5"]
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_delete_range():
+    """':d 5 8' deletes lines 5 through 8."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 11)]))
+    await editor.handle_input(":d 3 6")
+    expected = ["line 1", "line 2", "line 7", "line 8", "line 9", "line 10"]
+    assert editor.buffer == expected
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_delete_invalid_line():
+    """Deleting invalid line shows error."""
+    editor = Editor(initial_content="line 1\nline 2")
+    response = await editor.handle_input(":d 10")
+    assert "error" in response.output.lower() or "invalid" in response.output.lower()
+    assert editor.buffer == ["line 1", "line 2"]
+
+
+@pytest.mark.asyncio
+async def test_replace_line():
+    """':r 5 text' replaces line 5 with 'text'."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 6)]))
+    await editor.handle_input(":r 3 replaced text")
+    assert editor.buffer[2] == "replaced text"
+    assert len(editor.buffer) == 5
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_search_and_replace_first():
+    """':s old new' replaces first occurrence."""
+    editor = Editor(initial_content="hello world\nhello again\nhello there")
+    await editor.handle_input(":s hello hi")
+    assert editor.buffer[0] == "hi world"
+    assert editor.buffer[1] == "hello again"
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_search_and_replace_all():
+    """':sa old new' replaces all occurrences."""
+    editor = Editor(initial_content="hello world\nhello again\nhello there")
+    await editor.handle_input(":sa hello hi")
+    assert editor.buffer[0] == "hi world"
+    assert editor.buffer[1] == "hi again"
+    assert editor.buffer[2] == "hi there"
+    assert editor.dirty is True
+
+
+@pytest.mark.asyncio
+async def test_search_replace_no_match():
+    """Search/replace with no match shows message."""
+    editor = Editor(initial_content="hello world")
+    response = await editor.handle_input(":s foo bar")
+    assert (
+        "not found" in response.output.lower() or "no match" in response.output.lower()
+    )
+
+
+@pytest.mark.asyncio
+async def test_undo():
+    """':u' undoes last buffer change."""
+    editor = Editor(initial_content="line 1\nline 2")
+    await editor.handle_input("line 3")
+    assert len(editor.buffer) == 3
+    response = await editor.handle_input(":u")
+    assert editor.buffer == ["line 1", "line 2"]
+    assert "undo" in response.output.lower()
+
+
+@pytest.mark.asyncio
+async def test_undo_multiple_times():
+    """Undo can be called multiple times."""
+    editor = Editor(initial_content="line 1")
+    await editor.handle_input("line 2")
+    await editor.handle_input("line 3")
+    await editor.handle_input(":u")
+    await editor.handle_input(":u")
+    assert editor.buffer == ["line 1"]
+
+
+@pytest.mark.asyncio
+async def test_undo_when_empty():
+    """Undo with no history shows message."""
+    editor = Editor()
+    response = await editor.handle_input(":u")
+    assert (
+        "nothing to undo" in response.output.lower()
+        or "no undo" in response.output.lower()
+    )
+
+
+@pytest.mark.asyncio
+async def test_save():
+    """':w' calls save callback."""
+    saved_content = None
+
+    async def save_callback(content: str):
+        nonlocal saved_content
+        saved_content = content
+
+    editor = Editor(initial_content="line 1\nline 2", save_callback=save_callback)
+    await editor.handle_input("line 3")
+    response = await editor.handle_input(":w")
+    assert response.saved is True
+    assert response.done is False
+    assert saved_content == "line 1\nline 2\nline 3"
+    assert editor.dirty is False
+
+
+@pytest.mark.asyncio
+async def test_save_without_callback():
+    """':w' without callback shows error."""
+    editor = Editor(initial_content="line 1")
+    response = await editor.handle_input(":w")
+    assert (
+        "cannot save" in response.output.lower() or "no save" in response.output.lower()
+    )
+
+
+@pytest.mark.asyncio
+async def test_save_and_quit():
+    """':wq' saves and quits."""
+    saved_content = None
+
+    async def save_callback(content: str):
+        nonlocal saved_content
+        saved_content = content
+
+    editor = Editor(initial_content="line 1", save_callback=save_callback)
+    response = await editor.handle_input(":wq")
+    assert response.saved is True
+    assert response.done is True
+    assert saved_content == "line 1"
+
+
+@pytest.mark.asyncio
+async def test_quit_when_dirty_warns():
+    """':q' when dirty warns and doesn't quit."""
+    editor = Editor(initial_content="line 1")
+    await editor.handle_input("line 2")
+    response = await editor.handle_input(":q")
+    assert response.done is False
+    assert "unsaved" in response.output.lower() or "save" in response.output.lower()
+
+
+@pytest.mark.asyncio
+async def test_quit_when_clean():
+    """':q' when clean quits successfully."""
+    editor = Editor(initial_content="line 1")
+    response = await editor.handle_input(":q")
+    assert response.done is True
+
+
+@pytest.mark.asyncio
+async def test_force_quit():
+    """':q!' quits without saving."""
+    editor = Editor(initial_content="line 1")
+    await editor.handle_input("line 2")
+    response = await editor.handle_input(":q!")
+    assert response.done is True
+    assert response.saved is False
+
+
+@pytest.mark.asyncio
+async def test_dot_saves_and_quits():
+    """'.' on its own line saves and quits (MOO convention)."""
+    saved_content = None
+
+    async def save_callback(content: str):
+        nonlocal saved_content
+        saved_content = content
+
+    editor = Editor(initial_content="line 1", save_callback=save_callback)
+    await editor.handle_input("line 2")
+    response = await editor.handle_input(".")
+    assert response.done is True
+    assert response.saved is True
+    assert saved_content == "line 1\nline 2"
+
+
+@pytest.mark.asyncio
+async def test_dirty_flag_tracking():
+    """Dirty flag is properly tracked."""
+    editor = Editor(initial_content="line 1")
+    assert editor.dirty is False
+
+    await editor.handle_input("line 2")
+    assert editor.dirty is True
+
+    # Mock save
+    saved_content = None
+
+    async def save_callback(content: str):
+        nonlocal saved_content
+        saved_content = content
+
+    editor.save_callback = save_callback
+    await editor.handle_input(":w")
+    assert editor.dirty is False
+
+
+@pytest.mark.asyncio
+async def test_help():
+    """':h' shows help."""
+    editor = Editor()
+    response = await editor.handle_input(":h")
+    assert ":w" in response.output
+    assert ":q" in response.output
+    assert ":i" in response.output
+    assert ":d" in response.output
+
+
+@pytest.mark.asyncio
+async def test_undo_stack_size_limit():
+    """Undo stack is capped at 50 entries."""
+    editor = Editor()
+    # Add 60 lines
+    for i in range(60):
+        await editor.handle_input(f"line {i}")
+    # Undo stack should be capped
+    assert len(editor.undo_stack) <= 50
+
+
+@pytest.mark.asyncio
+async def test_line_numbers_padded():
+    """Line numbers in view are left-padded."""
+    editor = Editor(initial_content="\n".join([f"line {i}" for i in range(1, 12)]))
+    response = await editor.handle_input(":")
+    # Line 1 should have padding, line 11 should not have extra padding
+    lines = response.output.split("\n")
+    # Find lines with numbers
+    assert any(" 1  line 1" in line for line in lines)
+    assert any("11  line 11" in line for line in lines)
+
+
+# Syntax highlighting tests
+
+
+@pytest.mark.asyncio
+async def test_view_buffer_with_python_includes_ansi():
+    """Viewing buffer with content_type=python includes ANSI codes."""
+    editor = Editor(
+        initial_content="def foo():\n    return 42",
+        content_type="python",
+        color_depth="16",
+    )
+    response = await editor.handle_input(":")
+    # Should contain ANSI escape codes from syntax highlighting
+    assert "\033[" in response.output
+    # Should contain the code
+    assert "def" in response.output
+    assert "foo" in response.output
+
+
+@pytest.mark.asyncio
+async def test_view_buffer_with_text_no_ansi():
+    """Viewing buffer with content_type=text does NOT include ANSI codes."""
+    editor = Editor(
+        initial_content="plain text line 1\nplain text line 2", content_type="text"
+    )
+    response = await editor.handle_input(":")
+    # Should NOT contain ANSI escape codes (plain line numbers)
+    assert "\033[" not in response.output
+    # Should contain plain line numbers
+    assert "1  plain text line 1" in response.output
+    assert "2  plain text line 2" in response.output
+
+
+@pytest.mark.asyncio
+async def test_view_specific_line_with_python_includes_ansi():
+    """Viewing a specific line with python content includes ANSI codes."""
+    content = "\n".join([f"def func{i}():\n    return {i}" for i in range(10)])
+    editor = Editor(
+        initial_content=content,
+        content_type="python",
+        color_depth="16",
+    )
+    response = await editor.handle_input(":5")
+    # Should contain ANSI escape codes from syntax highlighting
+    assert "\033[" in response.output
+    # Should contain code from the context window
+    assert "def" in response.output
+
+
+@pytest.mark.asyncio
+async def test_color_depth_passed_to_highlight():
+    """Color depth is passed through to highlight function."""
+    editor = Editor(
+        initial_content="x = 1\ny = 2",
+        content_type="python",
+        color_depth="256",
+    )
+    response = await editor.handle_input(":")
+    # Should contain ANSI codes (256-color formatter)
+    assert "\033[" in response.output
+    # Should contain the code
+    assert "x" in response.output
+    assert "y" in response.output
+
+
+@pytest.mark.asyncio
+async def test_empty_buffer_with_python_content_type():
+    """Empty buffer with content_type=python still works."""
+    editor = Editor(content_type="python", color_depth="16")
+    response = await editor.handle_input(":")
+    # Should show empty buffer message
+    assert "empty" in response.output.lower()
+
+
+@pytest.mark.asyncio
+async def test_undo_past_save_marks_dirty():
+    """Undoing after save should mark buffer dirty again."""
+    saved = []
+
+    async def cb(content: str):
+        saved.append(content)
+
+    editor = Editor(initial_content="line 1", save_callback=cb)
+    await editor.handle_input("line 2")  # dirty
+    await editor.handle_input(":w")  # clean
+    assert not editor.dirty
+    await editor.handle_input(":u")  # undo the append - should be dirty
+    assert editor.dirty

tests/test_editor_integration.py

@@ -0,0 +1,167 @@
+"""Tests for editor integration with the shell and command system."""
+
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from mudlib import commands
+from mudlib.commands.edit import cmd_edit
+from mudlib.editor import Editor
+from mudlib.player import Player
+
+
+@pytest.fixture
+def mock_writer():
+    writer = MagicMock()
+    writer.write = MagicMock()
+    writer.drain = AsyncMock()
+    return writer
+
+
+@pytest.fixture
+def mock_reader():
+    return MagicMock()
+
+
+@pytest.fixture
+def player(mock_reader, mock_writer):
+    return Player(name="TestPlayer", x=5, y=5, reader=mock_reader, writer=mock_writer)
+
+
+@pytest.mark.asyncio
+async def test_edit_command_enters_editor_mode(player):
+    """Test that edit command sets up editor mode."""
+    assert player.mode == "normal"
+    assert player.editor is None
+
+    await cmd_edit(player, "")
+
+    assert player.mode == "editor"
+    assert player.editor is not None
+    assert isinstance(player.editor, Editor)
+    assert player.mode_stack == ["normal", "editor"]
+
+
+@pytest.mark.asyncio
+async def test_edit_command_sends_welcome_message(player, mock_writer):
+    """Test that edit command sends welcome message."""
+    await cmd_edit(player, "")
+
+    assert mock_writer.write.called
+    output = "".join([call[0][0] for call in mock_writer.write.call_args_list])
+    assert "editor" in output.lower()
+    assert ":h" in output
+
+
+@pytest.mark.asyncio
+async def test_edit_command_sets_save_callback(player):
+    """Test that edit command sets up a save callback."""
+    await cmd_edit(player, "")
+
+    assert player.editor is not None
+    assert player.editor.save_callback is not None
+
+
+@pytest.mark.asyncio
+async def test_editor_handle_input_preserves_whitespace(player):
+    """Test that editor receives input with whitespace preserved."""
+    await cmd_edit(player, "")
+
+    # Simulate code with indentation
+    response = await player.editor.handle_input("    def foo():")
+
+    assert player.editor.buffer == ["    def foo():"]
+    assert response.done is False
+
+
+@pytest.mark.asyncio
+async def test_editor_done_clears_editor_and_pops_mode(player):
+    """Test that when editor returns done=True, mode is popped and editor cleared."""
+    await cmd_edit(player, "")
+
+    assert player.mode == "editor"
+    assert player.editor is not None
+
+    # Quit the editor
+    response = await player.editor.handle_input(":q")
+    assert response.done is True
+
+    # Simulate what the shell loop should do
+    player.editor = None
+    player.mode_stack.pop()
+
+    assert player.mode == "normal"
+    assert player.editor is None
+
+
+@pytest.mark.asyncio
+async def test_editor_save_callback_sends_message(player, mock_writer):
+    """Test that save callback sends confirmation to player."""
+    await cmd_edit(player, "")
+    mock_writer.reset_mock()
+
+    await player.editor.handle_input("test line")
+    response = await player.editor.handle_input(":w")
+
+    assert response.saved is True
+    # Save callback should have sent a message
+    assert mock_writer.write.called
+    output = "".join([call[0][0] for call in mock_writer.write.call_args_list])
+    assert "saved" in output.lower()
+
+
+@pytest.mark.asyncio
+async def test_edit_command_only_works_in_normal_mode(player):
+    """Test that edit command has mode='normal' restriction."""
+    # Push a different mode onto the stack
+    player.mode_stack.append("combat")
+
+    # Try to invoke edit command through dispatch
+    await commands.dispatch(player, "edit")
+
+    # Should be blocked by mode check
+    assert player.mode == "combat"
+    assert player.editor is None
+
+
+@pytest.mark.asyncio
+async def test_mode_stack_push_and_pop(player):
+    """Test mode stack mechanics for editor mode."""
+    assert player.mode_stack == ["normal"]
+    assert player.mode == "normal"
+
+    # Enter editor mode
+    player.mode_stack.append("editor")
+    assert player.mode == "editor"
+    assert player.mode_stack == ["normal", "editor"]
+
+    # Exit editor mode
+    player.mode_stack.pop()
+    assert player.mode == "normal"
+    assert player.mode_stack == ["normal"]
+
+
+@pytest.mark.asyncio
+async def test_empty_input_allowed_in_editor(player):
+    """Test that empty lines are valid in editor mode (for blank lines in code)."""
+    await cmd_edit(player, "")
+
+    # Empty line should be appended to buffer
+    response = await player.editor.handle_input("")
+    assert response.done is False
+    assert player.editor.buffer == [""]
+
+
+@pytest.mark.asyncio
+async def test_editor_prompt_uses_cursor(player):
+    """Test that editor prompt should show line number from cursor."""
+    await cmd_edit(player, "")
+
+    # Add some lines
+    await player.editor.handle_input("line 1")
+    await player.editor.handle_input("line 2")
+
+    # After appending, cursor should be at the last line (1 in 0-indexed)
+    # This test verifies the cursor field exists and can be used for prompts
+    assert player.editor.cursor == 1
+    # Shell loop prompt: f"  {player.editor.cursor + 1}> " = "  2> "

tests/test_highlight.py

@@ -0,0 +1,125 @@
+"""Tests for syntax highlighting module."""
+
+from mudlib.render.highlight import highlight
+
+
+def test_highlight_python_returns_ansi_codes():
+    """Test that Python code returns string with ANSI escape codes."""
+    code = "def foo():\n    return 42"
+    result = highlight(code, language="python")
+    # Should contain ANSI escape codes
+    assert "\033[" in result
+    # Should contain the original code somewhere
+    assert "def" in result
+    assert "foo" in result
+
+
+def test_highlight_toml_returns_ansi_codes():
+    """Test that TOML code returns string with ANSI escape codes."""
+    code = '[section]\nkey = "value"'
+    result = highlight(code, language="toml")
+    # Should contain ANSI escape codes
+    assert "\033[" in result
+    # Should contain the original code somewhere
+    assert "section" in result
+    assert "key" in result
+
+
+def test_highlight_truecolor_depth():
+    """Test with color_depth=truecolor uses appropriate formatter."""
+    code = "x = 1"
+    result = highlight(code, language="python", color_depth="truecolor")
+    # Should contain ANSI codes (either 256-color or truecolor format)
+    assert "\033[" in result
+    # Should contain the code
+    assert "x" in result
+
+
+def test_highlight_256_depth():
+    """Test with color_depth=256 uses 256-color formatter."""
+    code = "x = 1"
+    result = highlight(code, language="python", color_depth="256")
+    # Should contain ANSI codes
+    assert "\033[" in result
+    # Should contain the code
+    assert "x" in result
+
+
+def test_highlight_16_depth():
+    """Test with color_depth=16 uses basic terminal formatter."""
+    code = "x = 1"
+    result = highlight(code, language="python", color_depth="16")
+    # Should contain ANSI codes
+    assert "\033[" in result
+    # Should contain the code
+    assert "x" in result
+
+
+def test_highlight_unknown_language_returns_original():
+    """Test unknown language returns original text unmodified (no crash)."""
+    code = "some random text"
+    result = highlight(code, language="unknown_language_xyz")
+    # Should return original text unchanged
+    assert result == code
+    # Should not contain ANSI codes
+    assert "\033[" not in result
+
+
+def test_highlight_empty_string():
+    """Test empty string input returns empty string."""
+    result = highlight("", language="python")
+    assert result == ""
+
+
+def test_highlight_no_extra_trailing_newlines():
+    """Test that output doesn't end with extra newlines."""
+    code = "x = 1"
+    result = highlight(code, language="python")
+    # Pygments tends to add a trailing newline, we should strip it
+    # The original code has no trailing newline, so neither should the result
+    assert not result.endswith("\n\n")
+    # A single trailing newline might be ok if original had one,
+    # but our test input doesn't, so result shouldn't either
+    assert not result.endswith("\n")
+
+
+def test_highlight_with_line_numbers():
+    """Test highlighting with line numbers enabled."""
+    code = "def foo():\n    return 42\n    return 99"
+    result = highlight(code, language="python", line_numbers=True)
+    # Should contain line numbers
+    assert "1" in result
+    assert "2" in result
+    assert "3" in result
+    # Should still contain ANSI codes
+    assert "\033[" in result
+    # Should contain the code (split by ANSI codes, so check separately)
+    assert "def" in result
+    assert "foo" in result
+    assert "return" in result
+    assert "42" in result
+
+
+def test_highlight_line_numbers_use_ansi_dim():
+    """Test that line numbers use ANSI dim/gray styling."""
+    code = "x = 1\ny = 2"
+    result = highlight(code, language="python", line_numbers=True)
+    # Line numbers should have some ANSI styling
+    # We'll check that there are escape codes before the digits
+    assert "\033[" in result
+    # This is a bit fragile, but we can check that the result
+    # starts with an escape code (for line number 1)
+    lines = result.split("\n")
+    # First line should start with escape code or digit
+    assert lines[0][0] in ("\033", "1", " ")
+
+
+def test_highlight_preserves_code_with_trailing_newline():
+    """Test code with trailing newline is handled correctly."""
+    code = "x = 1\n"
+    result = highlight(code, language="python")
+    # Should contain the code
+    assert "x" in result
+    # Should not accumulate extra newlines beyond what Pygments naturally adds
+    # We strip the trailing newline, so even input with \n shouldn't get extra
+    assert not result.endswith("\n\n")

tests/test_player_caps.py

@@ -0,0 +1,48 @@
+"""Tests for Player client capabilities integration."""
+
+from mudlib.caps import ClientCaps
+from mudlib.player import Player
+
+
+def test_player_default_caps():
+    """Player has default 16-color ANSI caps when created without explicit caps."""
+    player = Player(name="TestPlayer", x=0, y=0)
+    assert player.caps.ansi is True
+    assert player.caps.colors_256 is False
+    assert player.caps.truecolor is False
+    assert player.color_depth == "16"
+
+
+def test_player_caps_truecolor():
+    """Player with truecolor caps reports truecolor depth."""
+    caps = ClientCaps(ansi=True, utf8=True, colors_256=True, truecolor=True)
+    player = Player(name="TestPlayer", x=0, y=0, caps=caps)
+    assert player.color_depth == "truecolor"
+
+
+def test_player_caps_256():
+    """Player with 256-color caps reports 256 depth."""
+    caps = ClientCaps(ansi=True, utf8=True, colors_256=True, truecolor=False)
+    player = Player(name="TestPlayer", x=0, y=0, caps=caps)
+    assert player.color_depth == "256"
+
+
+def test_player_caps_16():
+    """Player with basic ANSI caps reports 16 depth."""
+    caps = ClientCaps(ansi=True, utf8=True)
+    player = Player(name="TestPlayer", x=0, y=0, caps=caps)
+    assert player.color_depth == "16"
+
+
+def test_player_caps_property_delegates():
+    """Player.color_depth delegates to caps.color_depth."""
+    player = Player(name="TestPlayer", x=0, y=0)
+    # Modify caps and verify color_depth reflects the change
+    player.caps = ClientCaps(ansi=True, colors_256=True, truecolor=True)
+    assert player.color_depth == "truecolor"
+
+    player.caps = ClientCaps(ansi=True, colors_256=True, truecolor=False)
+    assert player.color_depth == "256"
+
+    player.caps = ClientCaps(ansi=True)
+    assert player.color_depth == "16"

uv.lock

@@ -108,6 +108,7 @@ name = "mudlib"
 version = "0.1.0"
 source = { editable = "." }
 dependencies = [
+    { name = "pygments" },
     { name = "telnetlib3" },
 ]
 
@@ -121,7 +122,10 @@ dev = [
 ]
 
 [package.metadata]
-requires-dist = [{ name = "telnetlib3", directory = "../../../../src/telnetlib3" }]
+requires-dist = [
+    { name = "pygments", specifier = ">=2.17.0" },
+    { name = "telnetlib3", directory = "../../src/telnetlib3" },
+]
 
 [package.metadata.requires-dev]
 dev = [