Add AGENTS.md (#312)

Adds `AGENTS.md` to document how AI agents should work in this Homebrew
tap repo:

- project overview + repo layout
- key formulae/casks + update scripts
- CI-aligned `brew test-bot` commands
- PR/commit expectations and common pitfalls (e.g., `sha256` ordering)

## Validation

- Not run locally (Homebrew `brew` is not available in this
environment). CI will run `brew test-bot` on the PR.

---
_Generated with [`mux`](https://github.com/coder/mux) • Model:
openai:gpt-5.2 • Thinking: xhigh_

Author: ThomasK33

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, macos-13]
+        os: [ubuntu-22.04, macos-15]
 
     runs-on: ${{ matrix.os }}
 

AGENTS.md

@@ -0,0 +1,148 @@
+You are an experienced, pragmatic software engineering AI agent. Do not over-engineer a solution when a simple one is possible. Keep edits minimal. If you want an exception to ANY rule, you MUST stop and get permission first.
+
+# Project Overview
+
+This repository is the **official Homebrew tap** for Coder. It contains Homebrew **formulae** (CLI tools) and **casks** (macOS packages) used by end-users via `brew install`.
+
+- **Primary tech:** Homebrew Formula/Cask DSL (Ruby).
+- **Other tech:** Bash helper scripts under `scripts/`.
+- **CI:** GitHub Actions runs `brew test-bot` (see `.github/workflows/test.yml`).
+
+Typical changes are version bumps (updating `version`, `url`, and `sha256`) and keeping tests/install stanzas aligned with Homebrew conventions.
+
+# Reference
+
+## Key directories
+
+- `Formula/`: Homebrew formulae (Ruby classes).
+- `Casks/`: Homebrew casks (Ruby DSL blocks).
+- `scripts/`: helper scripts for updating formula versions/hashes.
+- `.github/workflows/`: CI definition.
+
+## Key files
+
+- `Formula/coder.rb`: **Coder v2** CLI formula (macOS arm64/amd64 + Linux amd64).
+- `Formula/coder@1.rb`: **Coder v1** (legacy) CLI formula (`keg_only :versioned_formula`).
+- `Casks/coder-desktop.rb`: Coder Desktop (versioned pkg + pinned `sha256`).
+- `Casks/coder-desktop-preview.rb`: Deprecated preview cask (`sha256 :no_check`).
+- `formula_renames.json`: Maps historical formula names to current ones.
+- `scripts/update-v2.sh`: Updates `Formula/coder.rb` for a new v2 release.
+- `scripts/update-v1.sh`: Updates `Formula/coder@1.rb` for a new v1 release.
+
+# Essential commands
+
+> Prerequisite: most commands below require **Homebrew** (`brew`) to be installed.
+
+## Build
+
+- N/A: this is a tap repository (no compilation/build step in-repo).
+
+## Format
+
+- Format/style formulae & casks (Homebrew style checks):
+  ```sh
+  brew style
+  ```
+
+## Lint
+
+- Tap syntax checks (matches CI):
+  ```sh
+  brew test-bot --only-tap-syntax
+  ```
+
+## Test
+
+- Run the same test phase CI runs for pull requests:
+  ```sh
+  brew test-bot --only-formulae
+  ```
+
+> Note: `brew test-bot` is relatively heavy but is the most reliable way to match CI behavior for this repo.
+
+## Clean
+
+- CI cleanup phase (useful locally when iterating with `brew test-bot`):
+  ```sh
+  brew test-bot --only-cleanup-before
+  ```
+
+- CI setup phase (often needed after cleanup / on first run):
+  ```sh
+  brew test-bot --only-setup
+  ```
+
+## Development server
+
+- N/A.
+
+## Release/update helpers
+
+> Note: `scripts/update-*.sh` use GNU `sed` flags (`-z` and `-i` without a backup extension). They’re expected to run in a GNU `sed` environment (e.g., Linux). If you’re on macOS with BSD `sed`, run them in a Linux container or adjust the commands.
+
+- Update **Coder v2** formula (`Formula/coder.rb`):
+  ```sh
+  ./scripts/update-v2.sh "<version>" "<darwin-arm64-sha256>" "<darwin-amd64-sha256>" "<linux-amd64-sha256>"
+  ```
+
+- Update **Coder v1** formula (`Formula/coder@1.rb`):
+  ```sh
+  ./scripts/update-v1.sh "<version>" "<darwin-amd64-sha256>" "<linux-amd64-sha256>"
+  ```
+
+- Computing SHA256 for downloaded artifacts:
+  ```sh
+  # macOS
+  shasum -a 256 <file>
+
+  # Linux
+  sha256sum <file>
+  ```
+
+# Patterns
+
+## Version bumps (formulae)
+
+- Keep the `version` value and the `url` templates in sync.
+- For `Formula/coder.rb`, there are **three** `sha256` entries (macOS arm64, macOS amd64, Linux amd64).
+  - The update scripts replace the **1st/2nd/3rd** `sha256` occurrence; avoid reordering or inserting extra `sha256` lines without updating `scripts/update-v2.sh`.
+- Prefer **deterministic** `test do` blocks (fast, no external state). If tests must fail, use `shell_output(cmd, expected_exit_code)` like `Formula/coder.rb`.
+
+## Version bumps (casks)
+
+- Use a pinned `sha256` when the URL is versioned.
+- Use `sha256 :no_check` only when the URL is intentionally unversioned (as in the deprecated preview cask).
+
+# Anti-patterns
+
+- Don’t reorder `sha256` lines in formulae if you still rely on `scripts/update-*.sh` (they patch by “nth match”).
+- Don’t add network-dependent tests or long-running integration tests to formulae; Homebrew formula tests should be quick and reproducible.
+
+# Commit and Pull Request Guidelines
+
+## Before committing
+
+- Run at least:
+  ```sh
+  brew test-bot --only-tap-syntax
+  ```
+- If you changed formulae, also run:
+  ```sh
+  brew test-bot --only-formulae
+  ```
+
+## Commit messages
+
+Recent history uses concise, release-oriented subjects. Prefer:
+
+- `coder <version>` for `Formula/coder.rb` bumps (example: `coder 2.30.0`).
+- `coder@1 <version>` or similar for v1 bumps.
+- `Coder Desktop v<version>` for cask releases.
+
+## Pull requests
+
+In the PR description:
+
+- State **what changed** (which formula/cask + version).
+- Include **where the SHA256 values came from** (e.g., the upstream release artifacts you downloaded).
+- Include **what you ran** locally (or say “not run” if you couldn’t).