Severe CPU usage caused by repeated file-watcher re-registration

### Describe the Bug

I encountered a severe CPU issue with Pyrefly 1.1.1 in VS Code 1.129.0 on macOS 26.5.2 (M1
Pro, 16 GB RAM).

In a workspace containing over 20,000 files, including approximately 10,000 Python files,
the VS Code extension host continuously consumed 155–230% CPU. The system load average
reached 30–41, causing the machine to become extremely hot.

Process sampling showed repeated uv_fs_poll and uv_fs_stat activity. The Pyrefly log
continuously repeated this sequence:

DidChangeWatchedFiles
Re-registering file watchers
Invalidated state, prepare to recheck open files

The log grew by approximately 6.7 KB in 12 seconds, with 24 watcher re-registration cycles
in the last 240 lines.

After disabling Pyrefly:

- The Pyrefly process exited and its log stopped growing.
- VS Code extension-host CPU dropped to 4.6–6.6%.
- CPU idle time increased to approximately 70%.
- The one-minute load average dropped from 41 to 11 and continued decreasing.

This strongly suggests a feedback loop involving DidChangeWatchedFiles and file-watcher re-
registration. Please investigate this behavior. I can provide the full logs and process
sample if needed.

### Sandbox Link

_No response_

### (Only applicable for extension issues) IDE Information

_No response_

Reproduce the issue in a VS Code workspace with more than 20,000 files and inspect the Pyrefly log for repeated DidChangeWatchedFiles and watcher re-registration cycles. Trace the file-watcher handling from those log events; done means re-registration no longer loops and CPU usage remains low in the large workspace.

Written by the indexing model from the issue text.