What is the evidence that Allah holds us accountable for what we write, by analogy with the noble verse: "He utters no word but there is a [watcher] by him ready [to record]"?

Man is held accountable for his sayings and actions, not for his sayings alone. The sacred texts indicate this, including Allah's saying: "So woe to those who write the book with their own hands, then say, 'This is from Allah,' to exchange it for a small price. Woe to them for what their hands have written and woe to them for what they earn." And His saying: "And the book will be placed [for judgment], and you will see the criminals fearful of that within it, and they will say, 'Oh, woe to us! What is this book that leaves neither a small thing nor a large thing except that it has enumerated it?' And they will find what they did present [before them]. And your Lord wrongs no one." The verse mentioned in Surah Qaf includes both sayings and actions together.