What happened?

Follow-up to #5292, scoped to extension-provided OAuth login flows.

When an extension OAuth provider calls OAuthLoginCallbacks.onPrompt() more than once in the same login dialog, the current prompt's live input can also render in earlier prompt rows.

I reproduced this with a local extension provider named Prompt Repro: the first prompt asks for First prompt: with placeholder first-value, then the second prompt asks for Second prompt:. After submitting the first prompt and typing second-secret-demo into the second prompt, the first prompt row also shows > second-secret-demo.

The submitted values are still captured sequentially. The bug is visual/TUI-only, but it can reveal a secret such as an API key in a previous prompt slot.

Steps to reproduce

1. Install or load an extension that registers an OAuth provider whose oauth.login(callbacks) does:

   await callbacks.onPrompt({ message: "First prompt:", placeholder: "first-value" });
   await callbacks.onPrompt({ message: "Second prompt:" });

2. Start Pi and run /login.

3. Select Use a subscription.

4. Select the extension provider, for example Prompt Repro.

5. Submit the first prompt.

6. Type into the second prompt without submitting.

Observed:

First prompt:
e.g., first-value
> second-secret-demo

Second prompt:
> second-secret-demo

The original real-world flow was a LiteLLM extension that asks for a base URL, then an API key.

Expected behavior

Only the active prompt should render a live input. Previous prompt rows should remain visible as stable submitted text or otherwise stop rendering the active input value.

A fix should preserve auth content already shown by onAuth() before onPrompt(); the whole login dialog should not be cleared between prompts.

Version

0.78.1