Fixes#50526
Fixes https://github.com/zed-industries/zed/issues/42841
Fixes https://github.com/zed-industries/zed/issues/49875
### Summary
Fix `autosave: on_focus_change` not firing reliably when leaving editors
with nested focus targets (e.g. multibuffer/search flows).
### Root cause
Autosave on focus change was wired to `on_blur` of the item focus
handle.
`on_blur` only fires when that exact handle is the focused leaf, which
misses common descendant-to-outside focus transitions.
## Fix
In `crates/workspace/src/item.rs`, switch autosave subscription from:
- `cx.on_blur(&self.read(cx).focus_handle(cx), ...)`
to:
- `cx.on_focus_out(&self.read(cx).focus_handle(cx), ...)`
Autosave behavior and guards remain unchanged:
- only for `AutosaveSetting::OnFocusChange`
- only when focus truly left the item (`!contains_focused`)
- skipped when modal is active (`!has_active_modal`)
### Impact
- Fixes missed autosaves when moving focus from item descendants to
other UI (terminal, file tree, search inputs, etc.).
- No behavior change for other autosave modes (`off`, `after_delay`,
`on_window_change`).
### Video
[Screencast from 2026-03-04
15-23-07.webm](https://github.com/user-attachments/assets/81135999-320f-40f3-9673-7c0460e5a14a)
Release Notes:
- Fixed an issue where `"autosave": "on_focus_change"` would not
reliably work in multibuffers.
---------
Co-authored-by: MrSubidubi <finn@zed.dev>
