Custom entries in the Servers list: named URLs with paths, other hosts and per-worktree ports

[danielhusar]

What I'd like

Let a project add its own entries to the Servers list in thread details: a name and a URL, where the URL can take the port T3 detected and add a path, query string or a different host.

Why

The Servers list is useful, but it only shows what port discovery finds: localhost:<port> and "Terminal · node". When I click a server I almost never want that bare address:

• Signing in automatically. My app's dev setup signs in a test user at /login?dev_user=true. That's the URL I open nearly every time, not /.
• A specific page. A local data explorer at /cdn-cgi/local/explorer, or a demo page at /demo/....
• The same port on another host. One demo page has to be on a different origin than the iframe it embeds, so it opens at http://[::1]:<port>/demo/sandbox while the frame stays on localhost. The same applies to 127.0.0.1 or a *.localhost subdomain.
• Telling servers apart. One pnpm dev starts the app, the marketing site and an inspector port. The list shows each one as "Terminal · node", so I can't tell which is which.
• Fixed URLs. Staging or a preview deployment would be handy in the same list.

The port also isn't fixed. Several worktrees of the same repo run at once, so the dev script takes the next free port in each (5173, 5174, …). That's why a project action's Preview URL doesn't help: it's a fixed string, so it points at the wrong worktree's app.

A possible shape

A file checked into the repo (or the same thing in project settings), for example .t3/servers.json:

[
  // {port} and {origin} come from the detected server this entry matched
  { "name": "App (signed in)", "match": { "port": 5173 }, "url": "{origin}/login?dev_user=true" },
  { "name": "Local data", "match": { "port": 5173 }, "url": "{origin}/cdn-cgi/local/explorer" },
  { "name": "Sandbox demo", "match": { "port": 5173 }, "url": "http://[::1]:{port}/demo/sandbox" },
  { "name": "Marketing site", "match": { "port": 8787 }, "url": "{origin}" },
  // no match: always shown
  { "name": "Staging", "url": "https://staging.example.com" }
]

• match.port would mean "the first port at or above this one that belongs to this thread", so each worktree gets its own app with no changes to the file. Matching on the command line, or on the URL the server printed in the terminal, would work too.
• An entry with a match shows only while that server is running. An entry without one is always there.
• Detected ports that match nothing stay listed as they are today, or can be hidden with a setting.
• On a remote environment, the URLs get the same forwarding that detected ports already get.

Another option: give the dev script a way to tell T3 its URLs while it runs, such as a t3 command or a file it writes. Then the script that picks the port also names the links.

Related: #15238 (the sidebar doesn't show a thread's dev servers) and #4746 (the browser lists local servers awkwardly).