fix(channels): read a channel and its open thread when returning to it - #1835

…pen conversation, describe toolbar badges (#2275)

## Summary

AIDA-2353. This PR has been cut down so it doesn't overlap two open PRs:
- **#2337** owns the Inbox unread count. tulsi left design feedback
there.
- **#2401** and its stack own finding replies in your threads and old
roots.

The badge, older-thread discovery and the 30-day discovery window that
used to be here were dropped in favor of those PRs. What's left is what
neither of them covers, plus one reading fix from beta feedback:

- **Solo chats in Inbox.** Ordinary incoming top-level responses in a
Solo chat appear as one flat conversation under All. They stay out of
DMs, matching the sidebar's separate Solo and Direct messages sections.
Its nested threads stay separate, and agent-only coordination and system
events stay out. A fresh Solo response reopens an archived flat row, the
same way ordinary DM activity does. Opening the flat row reads it in one
save (`markTimelineRead`): the channel catch-up mark covers ordinary
responses, as at the live bottom, and mentions get individual marks, so
thread rows stay unread. (`unread.ts` evidence filter and
`markTimelineRead`, `InboxItem.timeline`, `archive.ts` ordinary-activity
check.)
- **Toolbar page badges are announced.** In the toolbar placement a
page's badge sits beside its icon-only button, not inside it.
`PageNavigation` now points the button's `aria-describedby` at the
badge, so focusing the button announces its count. This applies to
#2337's Inbox count and Reminders' due count.
- **Live replies in the open conversation are read.** Reported in beta
feedback: a conversation open in the Inbox reader kept showing unread
after a new reply arrived. Opening a row leaves focus on the list, and
the reader's focus gate (`use-reading.ts`) only granted side-pane
reading to Channels' plain visits (`data-reading-thread`, #1835).
`PageTabs` now sets the same grant while the page shows its own content
in the main pane and a selected tab in the side pane. A tab moved to the
main pane still reads only by its own focus, and the reply must still be
in view. New `inbox-live-read.spec.mjs` fails without the fix.
- **Selection survives page navigation (tests only).** This behavior is
already on main. New regression coverage:
- `inbox-restoration.spec.mjs` (real shell) leaves Inbox for Messages
and Reminders and comes back.
  - An RTL check that restoring the page doesn't replay the row's read.

## Tests

- Full Vitest, `tsc --noEmit` and `biome check` pass.
- `inbox-live-read` passes 10/10 repeated in Chromium and WebKit, and
fails in both without the `PageTabs` change.
- Chromium: `inbox-live-read`, `inbox-restoration`, `inbox`,
`thread-unread` and `page-placement` pass. Vitest for
`bundled/channels`, `bundled/inbox` and `use-reading` passes.
- Toolbar description:
- Chromium's AX tree (via CDP) reports name "Inbox" and description "3
unread conversations".
  - Playwright's `toHaveAccessibleDescription` passes in WebKit.
- jsdom's accname reads the wrapper text instead, so the unit test
asserts the `aria-describedby` association.

## Checklist

- Agent review: an independent review of the reading grant found no
defects (closed or kept-mounted panes, inert retained tabs and main-pane
tabs never get the grant; only Inbox uses `ui.Tabs`).
- Agent exercise: Playwright journeys above, in Chromium and WebKit.
- Human test: tulsi tested Solo rows under All and the open-conversation
read in the desktop dev app (2026-11-04).

buzz-review-completed

## Not covered

- Older Solo activity outside the retained unread evidence isn't fetched
here. #2401's per-channel windows cover it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: tulsi <[email protected]>
Co-authored-by: BasilBot <399581b6165ab01343e3a1324774b1024d76942aea563468f93c975e5ee5193c@buzz.block.builderlab.xyz>
Co-authored-by: Claude Opus 5.5 <[email protected]>