I came across this while tackling another block map sync issue.

When a block is anchored past the point where its line soft wraps,
inserting or removing it invalidated the wrong range of rows. Inserting
such a block alone could silently not show it, and removing it could
leave the block on screen.

To reproduce: 

```sh
SEED=113 ITERATIONS=1 cargo test -p editor test_random_blocks
```

Release Notes:

- Fixed inline assistant prompt sometimes not appearing, or lingering
after dismissal, when that line was soft-wrapped.