downstream Bazel@HEAD failures: "Received more bytes than Content-length"

There are a number of downstream projects failing with Bazel@HEAD, and culprit finder is no help. Perhaps some infrastructure change?

Error occurs while downloading repository dependencies, and is of the form:
```
Received more bytes than Content-Length. Bytes read 4897 but wanted 4723
```

This is affecting:
[Kythe](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/2169#2429ff6c-a566-4f3e-bbf0-ffe67870a65e)
[rules_docker](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/2169#79c4dac2-2e02-4419-a6ed-84825731e224)
[rules_haskell](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/2169#c4572702-2cf3-40c0-a5d6-b63a4161647b)
[rules_jvm_external](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/2169#8580ae9d-9cd3-4bc9-8a19-664ed995c7ef)
[rules_kotlin](https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/2169#408ec837-c657-4b54-a627-dc1906b2d1f0)

Start with the linked Buildkite downstream failures for Kythe, rules_docker, rules_haskell, rules_jvm_external, and rules_kotlin, then compare their repository-dependency download errors. Done means identifying whether a shared CI or infrastructure change causes the Content-Length mismatch and restoring successful downstream builds.

Written by the indexing model from the issue text.