Nuxt CLI 4.0 reserves its agent-ready error overlay for apps on Nuxt 4.6

Dev-time errors now render with my-bad, which replaces youch ^[3]. The CLI only does this in full on Nuxt 4.6, the framework release it ships alongside ^[1][7]. On an older Nuxt, my-bad handles the failures the CLI sees itself, such as startup and config errors, and every other error goes to youch as before ^[7]. A team that bumps the CLI and leaves the framework alone gets the new config-error page and keeps its old request errors.

The agent feature sits inside the overlay that needs 4.6. Expanded, the overlay shows the code frame in the developer's own file, a call stack with framework frames folded away, the chain of Vue components involved, details of the request with its environment, and the server log output from before the failure ^[4]. Its Copy error button offers several formats. One of them is a prompt meant to be handed straight to an AI agent ^[5]. For a team that already debugs with an AI coding tool, the failure and its context are one copy away from that tool. The release notes do not say how much time this saves.

CLI 4.0 is a major version with more than 200 commits since v3.37 ^[2], and the highlights do not list what breaks. According to the release notes, the work centred on nuxt dev: how quickly it starts, the information it shows and what happens when something goes wrong ^[13]. The maintainers also say it resolves almost all open issues ^[2]. CI output stays plain by design. The new terminal panel falls back to a stream of logs in CI, when output is not a terminal, when a debugger is attached or when the window is too small, and `--no-tui` or `NUXT_TUI=plain` restores the classic output ^[11].

The error channel now lives in the CLI itself, mounted at devServer.errorChannel with a default path of /__nuxt_dev__/error ^[6]. Because the CLI owns it, the channel survives restarts of the app process and can report errors before Nuxt is up at all ^[6]. Only loopback peers get it in full. On a dev server exposed to the network, remote peers see a scoped view without request details or error history ^[8].

Moving the framework to 4.6 alongside the CLI is the only route to the overlay, the source-mapped SSR traces and the component traces ^[7]. I think that pairing is the decision for this quarter. Next quarter's work falls to module authors. The CLI adds three primitives for modules that want to work with the new terminal panel, withTerminal(), startTask() and notify(), and a module needs @nuxt/kit v4.6 as a dependency to use them ^[10]. The panel fills in as those dependencies move.