brew.env with brew install

[adam-moss]

Output of brew config

% brew config
HOMEBREW_VERSION: 5.0.14
ORIGIN: https://github.com/Homebrew/brew
HEAD: 6e88ffd4d26b5074cdbcad13f7dcff4222e8677f
Last commit: 2 days ago
Branch: stable
Core tap JSON: 10 Feb 11:19 UTC
Core cask tap JSON: 10 Feb 11:19 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_API_DOMAIN: <redact>
HOMEBREW_ARTIFACT_DOMAIN: <redact>
HOMEBREW_ARTIFACT_DOMAIN_NO_FALLBACK: set
HOMEBREW_CASK_OPTS: ["--require-sha --no-quarantine --appdir=/Users/adam.moss/Applications"]
HOMEBREW_DOCKER_REGISTRY_BASIC_AUTH_TOKEN: set
HOMEBREW_DOWNLOAD_CONCURRENCY: 24
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 12
HOMEBREW_NO_ANALYTICS: set
HOMEBREW_NO_ENV_HINTS: set
HOMEBREW_NO_INSECURE_REDIRECT: set
Homebrew Ruby: 3.4.8 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.8/bin/ruby
CPU: dodeca-core 64-bit arm_lobos
Clang: 17.0.0 build 1700
Git: 2.52.0 => /opt/homebrew/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.2-arm64
CLT: 26.2.0.0.1.1764812424
Xcode: N/A
Rosetta 2: false

Output of brew doctor

% brew doctor
Your system is ready to brew.

Description of issue

I have HOMEBREW_* env variables set in brew.env. There are being correctly shown when doing a brew config per the above, but when brew install is called they do not appear to be used.

If I export the variables directly via my .zshenv they are used.

Am I misunderstanding the purpose of brew.env? Are variables set this way being filtered out of the homebrew install environment?

I have verified that at

https://github.com/Homebrew/brew/blob/5457825968ba56db31de8a6fe9d7ec674e07055c/bin/brew#L312

${FILTERED_ENV[@]} does contain all of my entries from brew.env

Thanks