Feature: network route --delay <ms> to hold a matching request before continuing, aborting, or fulfilling it

[finnan444]

Use case

Agent-driven QA of a web app on a local dev server. Several checks need one request to be slow while everything else stays fast:

• Loading and skeleton states. On localhost an API call completes in 30 to 60 ms, so the state the team built never appears on a screenshot.
• Request ordering. A page that fires the same endpoint several times (for example a list and a widget both calling /api/content-issue/list) should either serialize or cancel the stale one. You can only observe that by delaying one of the calls.
• Timeout and retry paths in the client.

network route today can only abort a request or replace its response. Both produce an instant result, so none of the cases above are reachable from the CLI.

Today's options

• set offline on and --abort are instant. They test the failure branch, not the slow branch.
• Overriding window.fetch with an init script (--init-script) that reads rules from sessionStorage works for fetch and survives client-side navigation and reload. It does not see XHR, sendBeacon, resource loads, or server-side requests, and every project has to carry and maintain the shim.
• Adding a setTimeout to the server route handler is invasive and is easy to leave behind.

Proposed

agent-browser network route "**/api/content-issue/list" --delay 2000
agent-browser network route "**/api/i18n/list" --delay 5000 --abort
agent-browser network route "**/api/i18n/list" --delay 500 --body '{"items":[]}'

--delay <ms> holds the paused request for the given time and then applies the rest of the rule: continue unchanged when no other flag is set, abort with --abort, or fulfill with --body. Routes that match the same URL keep their current precedence.

A related gap, probably a separate change: RouteEntry.response already carries status, contentType, and headers in the daemon, but the CLI only exposes --body. A --status <code> flag would cover the "API returns 500" case without a custom body.

Implementation hint

Routes are matched in the Fetch.requestPaused handler in cli/src/native/actions.rs. A delay: Option<u64> field on RouteEntry, parsed in handle_route from a delay parameter, and a tokio::time::sleep before the existing Fetch.continueRequest / Fetch.failRequest / Fetch.fulfillRequest call should be enough. The handler is a background task that consumes Fetch.requestPaused events in a loop, so the sleep needs its own spawned task per request; otherwise one delayed request would hold back every other paused request.

The CLI parser for network route is in cli/src/commands.rs next to --abort and --body. type already has a --delay <ms> flag with number validation that can be reused.

Environment

agent-browser 0.41.0, macOS (darwin arm64), Chrome via agent-browser install. Checked against a SvelteKit app and a Next.js app on localhost.