Follow-up to #2304 (the "note" part discussed there).
When the selected page disappears from the page list,
`createPagesSnapshot()` silently re-selects the first page. The agent
gets no signal: if its next call is `list_pages` (which is what the
closed-page error message recommends), the listing already shows the new
selection and every subsequent tool call runs against a page the agent
never picked.
This PR records the automatic fallback and surfaces it as a one-line
note in the pages section of the same response:
```
## Pages
Note: the previously selected page was closed. Page 1 is now selected.
1: about:blank [selected]
```
For a selected page that is missing from the list without being closed,
the note reads "is no longer listed" instead. If the expectation from
#2304 holds (a page stays listed as long as it is not closed), that
wording never renders; if the transient case discussed there does occur
in the wild, the note will make it visible.
The fallback behavior itself is unchanged (as discussed in #2304, closed
tabs keep the browser-like auto-selection). No note is emitted on first
connect, when nothing was selected before.
Tests: two unit tests for the fallback bookkeeping (closed page, regular
selection), one for the missing-but-open case via a stubbed page list,
and the one affected snapshot updated (`close_page` now includes the
note).
Refs: #2304
## Motivation
`list_pages` shows each page's URL but not its title, which is painful
when multiple pages share a host — e.g. several tabs under
`app.example.com/u/0/`, `/u/1/`, `/u/2/`. There's no way to tell which
is which without visiting each one, even though every page has a usable
`document.title`.
Fixes#2156.
Closes#2175
## What this changes
- `list_pages` text output now shows the title before the URL when
available: `1: My Page (https://example.com) [selected]`. If the page
has no title (e.g. `about:blank`), the format is unchanged.
- The structured content entry for each page now includes a `title`
field alongside `id`, `url`, and `selected`.
- `page.title()` is awaited with a `.catch(() => '')` so a closed or
erroring page silently falls back to the URL-only format.
- `format()` is made `async` to support the `await` inside the page
loop; `createStructuredPage()` likewise becomes `async`.
## Testing
Start the MCP server with multiple tabs open. Call `list_pages` — pages
with titles now display as `id: Title (url)`. Pages without titles
(`about:blank`, data URLs) display as before.
---------
Co-authored-by: Piotr Paulski <31672205+zyzyzyryxy@users.noreply.github.com>
This is the first part of adding tests for checking tool behavior when a
dialog is already open (related to #1069)
In future CL, I will be focusing on tools which currently get blocked
due to open dialogs. As part of those CLs, proactive rejection of tool
execution will be implemented.
Thomas Bachem