esbuild using non-negligible CPU time when nothing is happening

### What versions & operating system are you using?

```
System:
OS: Linux 6.14 Ubuntu 24.04.3 LTS 24.04.3 LTS (Noble Numbat)
CPU: (88) x64 Intel(R) Xeon(R) w9-3575X
Memory: 202.60 GB / 250.93 GB
Container: Yes
Shell: 5.2.21 - /bin/bash
Binaries:
Node: 22.13.0 - /home/kenton/.volta/tools/image/node/22.13.0/bin/node
npm: 10.9.2 - /home/kenton/.volta/tools/image/node/22.13.0/bin/npm
pnpm: 10.22.0 - /home/kenton/.volta/bin/pnpm
npmPackages:
wrangler: ^4.50.0 => 4.50.0
```

### Please provide a link to a minimal reproduction

N/A

### Describe the Bug

When `wrangler dev` is running, but no changes are being made, I often catch `esbuild` using 5%-25% CPU. Why is `esbuild` even running when there are no changes?

### Please provide any relevant error logs

_No response_

Start with the `wrangler dev` entry point and observe the `esbuild` process while no files change. The report has no minimal reproduction, named files, or tests, so first establish a reproducible idle-CPU case; done should identify why work continues without changes and verify that idle CPU usage is reduced.

Written by the indexing model from the issue text.