repl: validate MCP tool names against Bedrock regex (closes #32)

Anthropic-via-Bedrock enforces ^[a-zA-Z0-9_-]{1,128}$ on tool names.
We already moved the alias separator from "." to "__" (commit f26cbd9),
but a future MCP server could still register a tool whose name (or whose
combination with the alias) contains characters outside that class —
silently breaking calls to strict providers.

connect_mcp now warns at startup for:
  - aliases containing "__" (would misparse on tool dispatch)
  - emitted alias__name strings that violate the regex or exceed 128 chars

Behavior preserved: validation is informative-only. tools_schema() still
emits the offending tool; local llama.cpp users accept lenient names
and shouldn't be penalized for downstream strictness.

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

repl.lua

@@ -142,6 +142,22 @@ function M.run(config)
         if sess.version_warning then
             renderer.status("mcp " .. alias .. ": " .. sess.version_warning)
         end
+        -- Tool-name validation (issue #32): Anthropic via Bedrock enforces
+        -- ^[a-zA-Z0-9_-]{1,128}$. We use "__" as the alias separator, so the
+        -- emitted name is alias__tool. Warn at startup; emit anyway so local
+        -- llama.cpp users aren't penalized for lenient downstreams.
+        if alias:find("__", 1, true) then
+            renderer.status(("mcp %s: alias contains '__' (used as separator); "
+                .. "tool dispatch will misparse"):format(alias))
+        end
+        for _, t in ipairs(sess:list_tools()) do
+            local full = alias .. "__" .. (t.name or "")
+            if #full > 128 or full:find("[^%w_-]") then
+                renderer.status(("mcp %s: tool name '%s' violates "
+                    .. "^[a-zA-Z0-9_-]{1,128}$ (will fail with strict providers "
+                    .. "e.g. anthropic via Bedrock)"):format(alias, full))
+            end
+        end
         return true, #sess:list_tools()
     end