## Homebrew on Apple Silicon — the official default prefix is /opt/homebrew

On Apple Silicon Macs, Homebrew installs to /opt/homebrew by default — not /usr/local. The official docs and the Aura CLI both expect this prefix.

On Apple Silicon (M1, M2, M3, M4), **Homebrew's default prefix is `/opt/homebrew`**. This is documented in the [official Homebrew Installation guide](https://docs.brew.sh/Installation): Apple Silicon installs there because `/usr/local` is the Intel-mac convention and the two prefixes are intentionally separated to avoid silent ABI mixing.

## Why Aura cares

Aura's install script and the `aura doctor` health check both detect the prefix automatically — but several agent-generated install scripts hard-code `/usr/local/bin` for the binary location, which silently fails on Apple Silicon. If `aura` is missing from your PATH after install, this is the most common reason.

## Quick check

```
# Confirm the prefix
brew --prefix
# /opt/homebrew  on Apple Silicon
# /usr/local     on Intel

# Confirm aura is installed under it
ls "$(brew --prefix)/bin/aura"

# If your shell can't find aura:
echo 'eval "$($(brew --prefix)/bin/brew shellenv)"' >> ~/.zprofile
source ~/.zprofile
```

## Why two prefixes exist at all

Homebrew's formulae are compiled per-architecture. Mixing an Intel-built bottle with an arm64 binary at runtime is undefined behaviour. The split prefix lets a single machine host both (helpful when you’re running an x86_64 Rosetta shell for legacy tools) without bottle-version collisions.

## Aura's rule

Aura assumes `/opt/homebrew` on Apple Silicon, `/usr/local` on Intel, and respects `$HOMEBREW_PREFIX` as an override. Anything else fails fast with a readable error from `aura doctor`.