fix(mcp): Allow several tool groups in btw_mcp_server()

The R file detection chained `is.character(tools) && file.exists(tools)`,
which errors under R >= 4.3 when `tools` names more than one tool group.
Use `is_string()` so the file branch only considers a single path.

Fixes #206

Author: taekop

NEWS.md

@@ -1,5 +1,7 @@
 # btw (development version)
 
+* `btw_mcp_server()` no longer errors when `tools` is a character vector naming more than one tool group, e.g. `btw_mcp_server(c("docs", "env", "sessioninfo"))` (@taekop, #206).
+
 # btw 1.5.0
 
 ## New features

R/mcp.R

@@ -165,7 +165,7 @@
 btw_mcp_server <- function(tools = NULL) {
   # If given a path to an R script, we'll pass it on to mcp_server()
   is_likely_r_file <-
-    is.character(tools) &&
+    is_string(tools) &&
     file.exists(tools) &&
     grepl("[.]r$", tools, ignore.case = TRUE)
 

tests/testthat/test-mcp.R

@@ -12,6 +12,16 @@ test_that("btw_mcp_server errors informatively with bad `tools`", {
   )
 })
 
+test_that("btw_mcp_server works with a character vector of multiple tool groups", {
+  local_enable_tools()
+  local_mocked_bindings(
+    mcp_server = function(...) "mocked",
+    .package = "mcptools"
+  )
+
+  expect_equal(btw_mcp_server(tools = c("docs", "env")), "mocked")
+})
+
 test_that("btw_mcp_tools() excludes skills group by default", {
   local_enable_tools()
   tools <- btw_mcp_tools()