feat(channels): move diagnostics into Channel Settings - #163

…search-send

* origin/main:
  Connect attachments to existing message delivery (#176)
  perf: preserve unchanged thread row identities (#171)
  perf: cache markdown preparation by content (#172)
  Add safe attachment upload groundwork (#150)
  feat: add sampling profiler launch modes (#148)
  feat(channels): remove DMs from the sidebar (#157)
  Distinguish namesake agents and selected recipients (#142)
  feat(channels): move diagnostics into Channel Settings (#163)
  Replace warning banners with shared Base UI toasts (#164)
  feat(shortcuts): add keyboard shortcut settings (#155)
  fix(channels): give floating unread cue an opaque panel surface (#153)
  feat(communities): add BUZZ_DEV_OPEN_RELAY to open the default relay on fresh dev ports (#151)
  Restore recipient avatars beside the composer mention tool (#162)
  Fix startup inventory duplication and late panel scroll shifts (#160)
  feat(channels): add channel creation (#138)
  Standardize Button and IconButton with Buzz design tokens (#145)

Signed-off-by: Zach Marley <[email protected]>

## Why

Clicking an image in a channel timeline cleared Channel settings and
unmounted the whole side pane for the length of the review. When the
viewer closed, Channel settings was gone with no announcement, and any
side panel that clears state on unmount had lost it: the native Huddle
chat panel releases files you had attached but not sent. The side thread
only survived because its text draft is saved per keystroke.

The `setSettings(undefined)` in `openMediaReview` dates from #163, when
settings was a transient panel auto-closed by any other opening. #413
made it a retained tab and added the dock guards but left that clear
behind.

## What

- `openMediaReview` no longer clears Channel settings.
- The side pane stays mounted under the viewer. `PanelDock` already
renders a closed dock as `hidden`, `inert` and `aria-hidden` when
`keepMounted` holds, so `keepMounted` now also holds during a review
(only when there is a panel to keep) and the pane's child guard no
longer unmounts on it. Settings, side plugin panels (Huddle) and the
Solo companion keep their state.
- Side thread tabs still leave during a review, via a new `hostPanes`
option on `useConversationTabs`. This is load-bearing, not a leftover:
the viewer's comment composer reads the thread draft when it mounts and
the thread composer reads the viewer's edits back when it remounts, so
keeping the side thread mounted would hand back a stale draft. Threads
moved to the main pane keep rendering through a review, as they did
before.

## Before / after

Left: `main` (3a1eb56). Right: this branch. Same steps: open ⋯
Channel actions → View channel details, click the image, press Escape.


https://github.com/user-attachments/assets/564548a1-7479-4855-9eb4-4090bfa1a844

![Final frame: on main the timeline stretches to the window edge with no
pane; on the branch Channel settings is still docked beside the timeline
with its tab
selected](https://github.com/user-attachments/assets/e7ecb1a5-ed99-4008-ac5d-655f770b85c4)

## Tests

- New browser journey in `tests/browser/channel-settings.spec.mjs`:
Channel settings stays open with its tab selected and focus returns to
the tile after Escape; the dock is `hidden` and `inert` under the modal;
a side-thread draft reaches the viewer's comment composer and comes back
edited; a thread moved to the main pane keeps the same composer element
connected through the review. Fails on `main` at the first pane
assertion.
- New `useConversationTabs` case: `hostPanes: ["main"]` withholds only
the side host and re-hosts it afterwards, including a tab the visit
showed but no longer selects.
- `channel-settings.spec.mjs` and the existing "media review hands off
the thread draft" journey pass in Chromium and WebKit; `tsc --noEmit`,
Biome and Vitest for `src/bundled/channels` and `src/features/panels`
are clean.

Not verified here: the native-only Huddle case (attached-but-unsent
files surviving a review) needs a manual check in the native app.

## Notes

- Merges with #2942 as a one-line, same-meaning conflict: that PR writes
`open={docked}`; keep that plus this branch's `keepMounted`.
- The other three `setSettings(undefined)` sites (Reply/open thread,
opening a link into a side panel, opening a bottom drawer) are unchanged
and belong in a follow-up once Channel settings is treated as a fully
retained tab.
- A main-pane thread on the same root as the reviewed image still keeps
its pre-viewer draft, as on `main`; the composer's conflict banner
surfaces it on the next keystroke. Unmounting only the reviewed root's
thread is a possible follow-up.

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

---------

Signed-off-by: mtoohey <[email protected]>
Co-authored-by: Claude Fable 5.1 <[email protected]>