fix(dap): validate attach_endpoint's arguments up front

The helper dereferences config.port/host and opts.label/default_port; a
malformed call (nil opts, missing label) crashed with a low-level "attempt to
index" instead of an actionable message. Assert both shapes at the top — same
clear-config-time-error purpose the function exists for, matching M.resolve's
spec.configure assert precedent. Verified: the two internal callers (delve,
python) still pass; nil/label-less calls now error clearly.

Author: charliie-dev

lua/modules/utils/dap.lua

@@ -30,6 +30,10 @@ end
 ---@param opts { label: string, default_port?: integer } @default_port omitted = port required.
 ---@return string host, integer port
 function M.attach_endpoint(config, opts)
+	-- Actionable config-time errors beat an opaque "attempt to index" deeper in
+	-- (this helper's whole purpose): guard the two shapes it dereferences.
+	assert(type(config) == "table", "attach_endpoint: config must be a table")
+	assert(type(opts) == "table" and type(opts.label) == "string", "attach_endpoint: opts.label (string) is required")
 	local port = opts.default_port
 	if config.port ~= nil then
 		local n = tonumber(config.port)