v1.2.1/#22: LMCP_HOST + LMCP_CONF env support

Adds two env vars to the packaged server.lua so hosts can switch
fully to the packaged entrypoint (combined with v1.2.0's tools.d/
plugin scan):

  LMCP_HOST — interface to bind on (default 0.0.0.0). Hosts that
              need .18-only binding (hertz) or similar single-NIC
              constraints set this. Threaded into lmcp.new opts.host.
  LMCP_CONF — path to a conf file with bearer-token entries (e.g.
              /opt/herding/etc/hertz-tools.conf). Read by lmcp.lua's
              read_conf; the `.godparticle` entry becomes the bearer
              token. Threaded into lmcp.new opts.conf.

Both unset → unchanged behavior (binds 0.0.0.0, no conf file).

Together with v1.2.0's tools.d/ scan, this lets a host like hertz
ship NO override server.lua — just an /opt/lmcp/tools.d/hertz.lua
plugin file and a systemd unit that points at the packaged
server.lua with LMCP_HOST=192.168.88.18 + LMCP_CONF=/opt/herding/
etc/hertz-tools.conf. apt upgrade then delivers all packaged
improvements automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server.lua

@@ -200,6 +200,13 @@ end
 local server_name = os.getenv("LMCP_NAME") or (WINDOWS and "windows-tools" or "linux-tools")
 local server = lmcp.new(server_name, {
     port = tonumber(os.getenv("LMCP_PORT") or arg[1]) or 8080,
+    -- LMCP_HOST: bind interface (default 0.0.0.0). Hosts that need
+    -- single-interface binding (hertz: 192.168.88.18 only) set this.
+    host = os.getenv("LMCP_HOST"),
+    -- LMCP_CONF: path to a conf file with bearer-token entries
+    -- (e.g. /opt/herding/etc/hertz-tools.conf). Read by lmcp.lua's
+    -- read_conf; the `.godparticle` entry becomes the bearer token.
+    conf = os.getenv("LMCP_CONF"),
 })
 
 -- ---- Tools ----
@@ -1066,6 +1073,46 @@ if WINDOWS then
     })
 end
 
+-- ---- host-local tool plugins (issue #22) ----
+-- Load every .lua file in LMCP_TOOLS_DIR (default /opt/lmcp/tools.d on POSIX,
+-- %ProgramData%\lmcp\tools.d on Windows). Each file is invoked as a function
+-- receiving the configured `server` instance and the `run` helper:
+--
+--     local server, run = ...
+--     server:tool("my_local_tool", "...", {...}, function(a) return run(...) end)
+--
+-- This is the standard plugin pattern (nginx conf.d/, systemd-tmpfiles.d, …).
+-- Hosts can ship their own tools alongside the packaged generics without
+-- forking the upstream server.lua.
+local plugin_dir = os.getenv("LMCP_TOOLS_DIR")
+    or (WINDOWS and (os.getenv("ProgramData") or "C:\\ProgramData") .. "\\lmcp\\tools.d"
+                 or "/opt/lmcp/tools.d")
+local list_cmd = WINDOWS
+    and ('dir /b "' .. plugin_dir .. '\\*.lua" 2>nul')
+    or  ('ls -1 "'  .. plugin_dir ..  '"/*.lua 2>/dev/null')
+local lh = io.popen(list_cmd)
+if lh then
+    for path in lh:lines() do
+        -- On Windows `dir /b` emits bare filenames; prefix the dir.
+        local full = path:match("[/\\]") and path
+                  or (plugin_dir .. (WINDOWS and "\\" or "/") .. path)
+        local chunk, err = loadfile(full)
+        if chunk then
+            local ok, perr = pcall(chunk, server, run)
+            if ok then
+                io.stderr:write("lmcp: loaded plugin " .. full .. "\n")
+            else
+                io.stderr:write("lmcp: plugin " .. full .. " errored: "
+                    .. tostring(perr) .. "\n")
+            end
+        else
+            io.stderr:write("lmcp: plugin " .. full .. " load error: "
+                .. tostring(err) .. "\n")
+        end
+    end
+    lh:close()
+end
+
 local transport = os.getenv("LMCP_TRANSPORT") or "http"
 if transport == "stdio" then
     if os.getenv("LMCP_PORT") then