The built-in sign-ins that come back to a port on this machine (Codex,
ChatGPT API, Devin, Kiro, Zed, Gemini, Antigravity) already took the
pasted address. Their plugins didn't: a subscription moved onto its plugin
(Devin, Kiro, Zed) or a plugin's own browser sign-in (Trae) showed only
"the account shows up here as soon as you're done", and a browser on
another computer than magpie's ended on a page that won't load with no way
to finish.
Now a plugin's "auto" sign-in whose page names a port on this machine to
come back to (redirect_uri, auth_callback_url, callback on localhost, or
Zed's native_app_port: loopbackPorts) sets pasteCallback, so the GUI shows
the same Callback URL field as the built-ins, and `magpie plugin login` /
`magpie accounts add` ask for it too. SubmitSignInCallback opens the pasted
address on 127.0.0.1 at that port, never through a proxy, so the plugin's
own listener finishes the sign-in as it would for the browser; an address
on another port or host is refused, a page that sends the browser on to a
page that comes back to the same port (Kiro's AWS sign-in) becomes the next
page to open. Command Code's page posts its key from script, which leaves
no address to paste, so it keeps offering the plugin's API key way.
Verified: TestPluginSignInTakesAPastedCallback (fake plugin with a loopback
sign-in, $FAKE_LOOPBACK) fails without the wiring in pluginBegin ("a
sign-in that comes back to a port here takes no pasted address:
{... PasteCallback:false ...}") and passes with it, -race -count=10;
TestLoopbackPorts covers the community plugins' page addresses.
go test -race ./internal/provider ./internal/plugin and the root package's
Plugin|Login|SignIn tests pass; vet, gofmt, darwin/linux nogui/windows
builds pass. With the real community Devin, Zed and Kiro plugins in a
sandbox HOME, each sign-in offered the field and a pasted address reached
the plugin's listener and the vendor (bogus code refused by Devin 401, Zed
"couldn't be decrypted", Kiro 400). signin-paste-plugin.test.cjs (new),
signin-callback and signin-paste-codex pass in Chromium and WebKit, en and
zh, at 360px; no new strings. Not tried: a real successful sign-in from a
browser on another computer.