v1.2.0/#22: tools.d/ plugin scan — host-local tool extensions

Adds a directory-scan plugin mechanism to the packaged server.lua
so hosts can drop their own tools alongside the packaged generics
without forking server.lua.

Mechanism:
- After all packaged tool registrations + before transport selection,
  the server scans LMCP_TOOLS_DIR (default /opt/lmcp/tools.d on POSIX,
  %ProgramData%\lmcp\tools.d on Windows) for *.lua files.
- Each plugin file is invoked as a function receiving (server, run):
    local server, run = ...
    server:tool("my_local_tool", "...", {...}, function(a) return ... end)
- Load errors and runtime errors are reported on stderr and skipped;
  the server continues with the tools it successfully loaded.

Why:
Hosts like hertz and ampere have always carried local /opt/lmcp/server.lua
overrides containing both packaged-overlap tools (shell, read_file, …)
AND host-specific tools (fritz, ha_api, mqtt_*, lxc_exec, …). When the
override drifts, the host either loses packaged improvements (the v1.1.1
fetch/web_search regression on hertz/ampere) or accumulates hand-merged
patches that vanish on shutdown (the original symptom in issue #22).
With tools.d/, hosts drop ONLY their custom tools as plugin files; the
packaged server.lua stays canonical. apt upgrade picks up new packaged
tools automatically.

Smoke-tested:
  $ mkdir -p /tmp/probe && cat > /tmp/probe/p.lua <<E
  local server, run = ...
  server:tool("plugin_probe", "test", {type="object"},
              function() return "ok" end)
  E
  $ LMCP_TOOLS_DIR=/tmp/probe lua server.lua
  lmcp: loaded plugin /tmp/probe/p.lua
  $ curl POST tools/list → plugin_probe present in the 10 tools listed

Existing single-file server deployments (no /opt/lmcp/tools.d/) keep
working unchanged — io.popen on a non-existent directory returns nil
and the plugin loop no-ops. Backwards compatible.

Closes the structural side of #22 (the ad-hoc-override pattern); ampere
+ hertz migration to use tools.d/ for their custom tools is the operator
follow-up.

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

lmcp.lua

@@ -163,10 +163,29 @@ end
 --     structuredContent (issue #13; spec-strict clients get first-class
 --     structured access)
 function lmcp:tool(name, description, params_schema, handler, opts)
+    -- Normalise empty inputSchema.properties → nil. JSON Schema allows
+    -- omitting `properties` on a `type: "object"` schema (means "any
+    -- object, no constraints"). Without this, an empty Lua properties
+    -- table goes through json.lua's is_array → emitted as `[]` →
+    -- spec-strict clients (Zod et al.) reject with
+    -- `expected: record, received: array`. The same gotcha already
+    -- bit `ping` in v1.0.0-rc1 (project_json_empty_table_gotcha
+    -- memory). v1.1.1 fix.
+    local schema = params_schema or { type = "object" }
+    if type(schema.properties) == "table" and next(schema.properties) == nil then
+        -- Clone the schema and drop the empty `properties` key. Avoids
+        -- mutating the caller's table (in case they re-use it across
+        -- registrations).
+        local clean = {}
+        for k, v in pairs(schema) do
+            if k ~= "properties" then clean[k] = v end
+        end
+        schema = clean
+    end
     self.tools[name] = {
         name = name,
         description = description,
-        inputSchema = params_schema or { type = "object", properties = {} },
+        inputSchema = schema,
         handler = handler,
         annotations  = opts and opts.annotations  or nil,
         outputSchema = opts and opts.outputSchema or nil,

server.lua

@@ -1066,6 +1066,46 @@ 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

windows/README.md

@@ -3,14 +3,30 @@
 This directory contains the WiX manifest and packaging files for the
 Windows MSI build of lmcp.
 
-## Workflow
+## Recommended: cross-build on Linux (one command)
 
 ```sh
-# 1. Pull the Lua + LuaSocket runtime into pkg/lua/ (one-time, see below).
+./build-msi.sh /path/to/output/dir
-# 2. Sync the lmcp .lua sources from the root of the repo:
+```
-./sync.sh
+
-# 3. Bump windows/lmcp.wxs `Version="…"` to match the release tag.
+Downloads Lua 5.4 Win64 binaries from LuaBinaries, cross-compiles
-# 4. Invoke WiX:
+LuaSocket via `mingw-w64`, stages `pkg/lua/`, and runs `wixl` to
+produce `lmcp-<version>.msi`. No Windows VM required.
+
+Prereqs on a Debian/Ubuntu builder:
+```sh
+sudo apt install wixl unzip gcc-mingw-w64-x86-64 \
+                 binutils-mingw-w64-x86-64 mingw-w64-x86-64-dev curl
+```
+
+Version comes from `lmcp.wxs` `Version="…"`. Bump that before
+building a release.
+
+## Alternative: build on Windows via WiX toolset
+
+```cmd
+sync.sh                                  REM see "tracked vs. generated"
+REM ensure pkg/lua/ has the runtime — see below
 candle.exe lmcp.wxs
 light.exe lmcp.wixobj -o lmcp-1.x.y.msi
 ```

windows/build-msi.sh

@@ -0,0 +1,100 @@
+#!/bin/sh
+# windows/build-msi.sh — produce lmcp-<ver>.msi on Linux via wixl.
+#
+# This is the first-time-discovered cross-build path: download Lua 5.4
+# Win64 binaries from LuaBinaries, cross-compile LuaSocket with mingw-w64,
+# stage windows/pkg/lua/, then invoke wixl on the WiX manifest.
+#
+# Avoids the VM106-clone + WiX-on-Windows path entirely. ~1 minute on a
+# warm cache; ~3-5 minutes cold (downloads ~700 KB + cross-compiles).
+#
+# Prereqs (apt install on Debian aarch64):
+#   apt-get install -y wixl unzip gcc-mingw-w64-x86-64 binutils-mingw-w64-x86-64 \
+#                      mingw-w64-x86-64-dev
+#
+# Usage: ./build-msi.sh [output_dir]
+#   Output: $output_dir/lmcp-<ver>.msi (default: $PWD)
+#
+# Version comes from windows/lmcp.wxs Version="…" attribute.
+set -eu
+
+here=$(dirname "$(readlink -f "$0")")
+root=$(cd "$here/.." && pwd)
+out_dir=${1:-$PWD}
+work=$(mktemp -d /tmp/lmcp-msi-XXXXXX)
+trap "rm -rf $work" EXIT
+
+# Versions — bump as upstream releases.
+LUA_VER=5.4.2
+LUASOCKET_VER=3.1.0
+
+# Pull current lmcp version from the WiX manifest.
+lmcp_ver=$(sed -n 's/.*Version="\([^"]*\)".*/\1/p' "$here/lmcp.wxs" | head -1)
+[ -n "$lmcp_ver" ] || { echo "build-msi.sh: cannot parse Version from lmcp.wxs" >&2; exit 1; }
+
+echo "build-msi.sh: lmcp $lmcp_ver, lua $LUA_VER, luasocket $LUASOCKET_VER"
+
+echo "==> 1/5 sync lmcp .lua sources into pkg/"
+"$here/sync.sh"
+
+echo "==> 2/5 fetch lua $LUA_VER win64 binaries + dev library"
+cd "$work"
+curl -sSLf -o lua-bin.zip \
+    "https://downloads.sourceforge.net/project/luabinaries/${LUA_VER}/Tools%20Executables/lua-${LUA_VER}_Win64_bin.zip"
+curl -sSLf -o lua-lib.zip \
+    "https://downloads.sourceforge.net/project/luabinaries/${LUA_VER}/Windows%20Libraries/Dynamic/lua-${LUA_VER}_Win64_dllw6_lib.zip"
+mkdir -p luabin lualib include/lua/54 include/lua54 bin/lua/54 bin/lua54 lib/lua/54 lib/lua54
+unzip -q -o lua-bin.zip -d luabin
+unzip -q -o lua-lib.zip -d lualib
+cp lualib/include/*.h include/lua/54/
+cp lualib/include/*.h include/lua54/
+cp lualib/liblua54.a lib/lua/54/
+cp lualib/liblua54.a lib/lua54/
+cp lualib/lua54.dll bin/lua/54/
+cp lualib/lua54.dll bin/lua54/
+
+echo "==> 3/5 cross-compile LuaSocket $LUASOCKET_VER for win64"
+curl -sSLf -o luasocket.tar.gz \
+    "https://github.com/lunarmodules/luasocket/archive/refs/tags/v${LUASOCKET_VER}.tar.gz"
+tar xzf luasocket.tar.gz
+cd "luasocket-${LUASOCKET_VER}"
+make -s PLAT=mingw \
+    CC=x86_64-w64-mingw32-gcc \
+    LD=x86_64-w64-mingw32-gcc \
+    LUAV=54 \
+    LUAINC_mingw_base="$work/include" \
+    LUALIB_mingw_base="$work/bin" \
+    > /dev/null
+
+echo "==> 4/5 stage pkg/lua/"
+pkg_lua="$here/pkg/lua"
+rm -rf "$pkg_lua"
+mkdir -p "$pkg_lua/socket" "$pkg_lua/mime"
+
+# WiX manifest expects "lua.exe" (not "lua54.exe").
+cp "$work/luabin/lua54.exe"        "$pkg_lua/lua.exe"
+cp "$work/luabin/lua54.dll"        "$pkg_lua/lua54.dll"
+cp src/socket.lua                  "$pkg_lua/"
+cp src/mime.lua                    "$pkg_lua/"
+cp src/ltn12.lua                   "$pkg_lua/"
+cp src/socket-3.0.0.dll            "$pkg_lua/socket/core.dll"
+cp src/ftp.lua                     "$pkg_lua/socket/"
+cp src/headers.lua                 "$pkg_lua/socket/"
+cp src/http.lua                    "$pkg_lua/socket/"
+cp src/smtp.lua                    "$pkg_lua/socket/"
+cp src/tp.lua                      "$pkg_lua/socket/"
+cp src/url.lua                     "$pkg_lua/socket/"
+cp src/mime-1.0.3.dll              "$pkg_lua/mime/core.dll"
+
+echo "==> 5/5 wixl: produce MSI"
+# wixl wants forward slashes; rewrite Windows-style backslashes in Source=.
+wxs_tmp="$work/lmcp.wxs"
+sed 's|Source="pkg\\|Source="pkg/|g; s|\\\([a-zA-Z]\)|/\1|g' "$here/lmcp.wxs" > "$wxs_tmp"
+mkdir -p "$out_dir"
+out_msi="$out_dir/lmcp-${lmcp_ver}.msi"
+(cd "$here" && wixl -v "$wxs_tmp" -o "$out_msi")
+
+echo ""
+echo "==> done: $out_msi"
+ls -la "$out_msi"
+sha256sum "$out_msi"