docs(install): document Homebrew (#1946)

* docs(install): document Homebrew

* docs(install): clarify the Node prerequisite

README.md

@@ -122,7 +122,7 @@ Solo, OpenSpec keeps you and your AI honest on a single repo. On a team, the har
 
 ## Quick Start
 
-**Requires Node.js 20.19.0 or higher.**
+**Requires Node.js 20.19.0 or higher.** Homebrew installs it as a dependency.
 
 Install OpenSpec globally:
 
@@ -130,6 +130,12 @@ Install OpenSpec globally:
 npm install -g @fission-ai/openspec@latest
 ```
 
+Or install the official [Homebrew formula](https://formulae.brew.sh/formula/openspec) on macOS or Linux:
+
+```bash
+brew install openspec
+```
+
 Then navigate to your project directory and initialize:
 
 ```bash
@@ -137,7 +143,7 @@ cd your-project
 openspec init
 ```
 
-> **Want your AI to do it?** Paste the [setup prompt](docs/installation.md#install-with-your-ai-assistant) into your coding assistant — it installs the CLI, runs `openspec init`, and verifies the result.
+> **Want your AI to do it?** Paste the [setup prompt](docs-lab/start/installation.md#install-with-your-ai-assistant) into your coding assistant — it installs the CLI, runs `openspec init`, and verifies the result.
 
 Now talk to your AI:
 
@@ -151,7 +157,7 @@ Both are in the default profile. If you want the expanded workflow (`/opsx:new`,
 > [!NOTE]
 > Not sure if your tool is supported? [View the full list](docs/supported-tools.md) – we support 30+ tools and growing.
 >
-> Also works with pnpm, yarn, bun, and nix. [See installation options](docs/installation.md).
+> Also works with Homebrew, pnpm, yarn, bun, and Nix. [See installation options](docs-lab/start/installation.md).
 
 ## Docs
 
@@ -208,6 +214,12 @@ AI coding assistants are powerful but unpredictable when requirements live only
 npm install -g @fission-ai/openspec@latest
 ```
 
+If you installed OpenSpec with Homebrew:
+
+```bash
+brew upgrade openspec
+```
+
 **Refresh agent instructions**
 
 Run this inside each project to regenerate AI guidance and ensure the latest slash commands are active:

docs-lab/start/installation.md

@@ -5,7 +5,9 @@
 
 ## Prerequisites
 
-OpenSpec is a Node.js CLI. You need version 20.19.0 or newer.
+OpenSpec runs on Node.js 20.19.0 or newer. Homebrew installs Node.js as a
+dependency, and the Nix package includes the runtime. Check your installed version
+before using another install method.
 
 In your terminal:
 
@@ -13,7 +15,9 @@ In your terminal:
 node --version
 ```
 
-If that prints `v20.19.0` or higher, you're set. If not, install a newer Node from [nodejs.org](https://nodejs.org) or through your version manager (nvm, fnm, asdf, volta).
+If that prints `v20.19.0` or higher, you're set. If not, install a newer Node from
+[nodejs.org](https://nodejs.org) or through your version manager (nvm, fnm, asdf,
+volta). You can skip this check when you install with Homebrew or Nix.
 
 The workflow itself runs inside an AI coding tool: Claude Code, Cursor, or any other tool on the [supported list](../reference/supported-tools.md).
 
@@ -53,6 +57,16 @@ In your terminal:
 npm install -g @fission-ai/openspec@latest
 ```
 
+### Homebrew
+
+Homebrew installs OpenSpec and its Node.js dependency on macOS or Linux. In your terminal:
+
+```bash
+brew install openspec
+```
+
+The formula is published in [homebrew-core](https://formulae.brew.sh/formula/openspec), so you don't need to add a tap.
+
 ### Yarn
 
 `yarn global add` is Yarn Classic (1.x) only. Modern Yarn removed global installs, so use npm, pnpm, or bun instead. A global CLI doesn't have to share your project's package manager.
@@ -123,7 +137,7 @@ When a newer CLI is out, [`openspec update`](../reference/cli.md#openspec-update
 
 
 > [!WARNING]
-> On Deno, re-run the [Deno install](#deno) with `-f`; it won't overwrite the installed command without it. On Nix, use `nix profile upgrade openspec`.
+> On Homebrew, run `brew upgrade openspec`. On Deno, re-run the [Deno install](#deno) with `-f`; it won't overwrite the installed command without it. On Nix, use `nix profile upgrade openspec`.
 
 > [!NOTE]
 > A global npm install belongs to one Node installation. Switch Node versions with nvm and the `openspec` command doesn't come along, so install it again under the new version.
@@ -144,7 +158,7 @@ openspec completion uninstall
 npm uninstall -g @fission-ai/openspec
 ```
 
-On Deno: `deno uninstall --global openspec`. On Nix: `nix profile remove openspec`. Your shell should no longer find `openspec`.
+On Homebrew: `brew uninstall openspec`. On Deno: `deno uninstall --global openspec`. On Nix: `nix profile remove openspec`. Your shell should no longer find `openspec`.
 
 **3. Delete what's left, or keep it.**