[## Context

Fixes a bug where the Bookmarks tab, opened via `editor: view
bookmarks`, showed a stale snapshot and had to be reopened to display
bookmarks added or removed while it was open.

Closes #56268

`view_bookmarks` built a one-time multibuffer and never subscribed to
`BookmarkStore`. The store also calls `cx.notify()` while resolving
serialized bookmarks into anchors, even though that bookkeeping does not
represent a user-visible bookmark change. Observing all notifications
would therefore feed resolution notifications back into the refresh
mechanism and cause redundant cancellation and requeue work. The store
now emits a dedicated `BookmarkStoreEvent::BookmarksChanged` from
bookmark mutation paths, while `resolve_all` deliberately does not emit
it.

Refresh state lives on a `BookmarksView` entity that holds the tab's
multibuffer. Split editors already share that multibuffer, so they share
the view as well. Each store event drives one reconciliation regardless
of how many split editors display it. The view remains alive as long as
any split retains it, so closing the original tab does not stop the
remaining split from refreshing.

Each refresh reconciles excerpts per path instead of rebuilding the
multibuffer: `set_excerpts_for_path` updates files that still contain
bookmarks, while `remove_excerpts` removes files whose final bookmark
was deleted. This follows the per-path reconciliation pattern used by
project diff views.

`view_bookmarks` creates the tab synchronously and populates it
asynchronously, following the existing patterns in
`ProjectDiagnosticsEditor::deploy` and
`ProjectSearchView::existing_or_new_search`. Repeated invocations focus
the existing Bookmarks tab instead of opening duplicates.

Video of the manual test:

[Screencast from 2026-05-11
02-03-38.webm](https://github.com/user-attachments/assets/8ac97245-09ff-4a79-9634-20cb8dfbb7eb)

## How to Review

**`crates/project/src/bookmark_store.rs`**

Adds `BookmarkStoreEvent::BookmarksChanged`, emitted from bookmark
mutation paths such as toggle, label edit, file rename or deletion,
clear, and deserialization, but not from anchor resolution. It also adds
`BookmarkStore::is_empty`.

**`crates/editor/src/bookmarks.rs`**

Adds `BookmarksView`, which holds the multibuffer, store subscription,
and in-flight refresh task. It reconciles excerpts and emits
`BookmarksViewEvent::Populated(ranges)` for per-editor highlights and
cursor placement. It also caches the latest populated ranges and replays
them when an editor attaches, allowing a split created after population
to display bookmark highlights immediately.

**`crates/editor/src/editor.rs`**

Adds the shared `bookmark_view`, a per-editor subscription to its
population events, and `bookmark_initial_selection_pending` for initial
cursor placement. `Editor::clone` attaches the split to the shared view
instead of creating another store subscription and refresh task.

**`crates/editor/src/editor_tests.rs`**

Adds five tests covering automatic addition and removal across multiple
files, removal of a file's path after its final bookmark is deleted,
initial cursor placement, a bookmark change racing initial population,
splitting while population is pending, cached highlights in a
late-attaching split, and continued refreshing after the original tab
releases its view handle.

## Self-Review Checklist

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the UI/UX checklist
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed Bookmarks tab not updating when bookmarks are added or removed
while the tab is open](https://github.com/zed-industries/zed/pull/56363)

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>