Harden /ask helper, UDP replies and run_lua in multiplayer

- Pass the /ask question to claude on stdin so it can't be parsed as a CLI option.
- Block run_lua in multiplayer unless an admin enables the new
  "Allow Lua queries in multiplayer" map setting.
- Ignore UDP packets that don't come from the game's port, in both the
  MCP server and the ask helper.
- Build the screenshot path from our own name instead of the game's reply,
  and restrict screenshot names in the mod.
- Validate ask packets, cap question length and limit concurrent claude runs.
- Replace hard-coded home paths in the README and systemd unit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -33,20 +33,21 @@ The game only listens on 127.0.0.1.
 
 **3. Register the MCP server.** Requires [uv](https://docs.astral.sh/uv/).
 
-Claude Code:
+Claude Code (run from this repo's root):
 
 ```bash
-claude mcp add factorio --scope user -e FACTORIO_UDP_PORT=34200 -- uv run --directory /home/faab/Documents/Code/Factorio/claude-co-engineer/server claude-co-engineer-mcp
+claude mcp add factorio --scope user -e FACTORIO_UDP_PORT=34200 -- uv run --directory "$PWD/server" claude-co-engineer-mcp
 ```
 
-Claude Desktop — add to `claude_desktop_config.json` (Settings → Developer → Edit Config), then restart it:
+Claude Desktop — add to `claude_desktop_config.json` (Settings → Developer → Edit Config), with
+`/path/to/claude-co-engineer` replaced by where you cloned this repo, then restart it:
 
 ```json
 {
   "mcpServers": {
     "factorio": {
       "command": "uv",
-      "args": ["run", "--directory", "/home/faab/Documents/Code/Factorio/claude-co-engineer/server", "claude-co-engineer-mcp"],
+      "args": ["run", "--directory", "/path/to/claude-co-engineer/server", "claude-co-engineer-mcp"],
       "env": { "FACTORIO_UDP_PORT": "34200" }
     }
   }
@@ -86,6 +87,10 @@ default, and are purely visual.
 your world changes, turn off **Allow Lua queries** in Settings → Mod settings → Map. Every query is
 logged to `factorio-current.log`.
 
+In multiplayer, `run_lua` is off unless an admin also turns on **Allow Lua queries in multiplayer**:
+the Lua runs for everyone, and text other players put in the world (station names, labels) ends up
+in what Claude reads, so it could be talked into changing things.
+
 ## Asking from inside the game
 
 Type `/ask <question>` in the game chat (e.g. `/ask why is my green science slow?`). The answer
@@ -100,16 +105,17 @@ the places it mentions get highlighted. Follow-up questions continue the same co
 This needs:
 
 - the `claude` CLI logged in with your subscription (`claude auth login`, once);
-- the helper running. Either start it by hand:
+- the helper running. Either start it by hand from this repo's root:
 
   ```bash
-  ~/Documents/Code/Factorio/claude-co-engineer/server/.venv/bin/claude-co-engineer-ask
+  uv run --directory server claude-co-engineer-ask
   ```
 
-  or install it as a systemd user service that starts at login:
+  or install it as a systemd user service that starts at login (from this repo's root; this fills in
+  its path):
 
   ```bash
-  cp server/claude-co-engineer-ask.service ~/.config/systemd/user/ && systemctl --user daemon-reload && systemctl --user enable --now claude-co-engineer-ask
+  uv sync --directory server && mkdir -p ~/.config/systemd/user && sed "s|/path/to/claude-co-engineer|$PWD|" server/claude-co-engineer-ask.service > ~/.config/systemd/user/claude-co-engineer-ask.service && systemctl --user daemon-reload && systemctl --user enable --now claude-co-engineer-ask
   ```
 
   Its log shows each question and answer: `journalctl --user -u claude-co-engineer-ask -f`.
@@ -120,7 +126,7 @@ your plan's usage. It's per player, so in multiplayer everyone picks their own.
 
 The dropdown entries are aliases, which the `claude` CLI resolves to the newest model of that name,
 so a new Sonnet or Opus is used automatically. To force any other model, uncomment
-`FACTORIO_ASK_MODEL_OVERRIDE` in `server/claude-co-engineer-ask.service` (an alias or a full model ID)
+`FACTORIO_ASK_MODEL_OVERRIDE` in `~/.config/systemd/user/claude-co-engineer-ask.service` (an alias or a full model ID)
 and run `systemctl --user daemon-reload && systemctl --user restart claude-co-engineer-ask`. It wins
 over the in-game setting for everyone.
 
@@ -128,7 +134,8 @@ Claude only gets the Factorio tools in these sessions: no shell, files or web. I
 running, the game tells you after 3 seconds. The helper's port is a map setting (Ask helper port, default 34201).
 Helper environment variables: `FACTORIO_ASK_PORT`, `FACTORIO_ASK_MODEL` (model when the game doesn't
 send one, default `sonnet`), `FACTORIO_ASK_MODEL_OVERRIDE` (always use this model),
-`FACTORIO_ASK_TIMEOUT` (300 s), `FACTORIO_ASK_CLAUDE` (path to the CLI).
+`FACTORIO_ASK_TIMEOUT` (300 s), `FACTORIO_ASK_MAX_CONCURRENT` (Claude runs at once across all players,
+default 2), `FACTORIO_ASK_CLAUDE` (path to the CLI). The helper only accepts packets from the game's UDP port.
 
 ## Ratio calculator