Previously, when a file change event arrived while a build was in progress
(i.e., client stage was not Success/Failed/Aborted), the event was logged
and silently discarded. This caused issues with tools like stylance,
tailwind watch, or sass --watch that generate output files in response
to source file changes.
The typical failure case:
1. User saves a .module.scss file
2. dx starts rebuilding
3. stylance CLI (watching the same file) regenerates stylance.css
4. dx receives the stylance.css change event but discards it
5. Build completes with stale CSS
Now, file changes that arrive during a build are queued in a
pending_file_changes vector and processed after the build completes.
Amos Wenger
e5a98d094d