cli: upgrade fails to detect Homebrew install from homebrew-core #52699

Summary

Installation-method detection fails for OpenCode installed from homebrew-core (brew install opencode), so /update and opencode upgrade abort with installation method not found even though brew is a supported --method.

Environment

• opencode version: v2.0.20
• OS: Darwin 25.6.0 (darwin arm64)
• Terminal: WezTerm (TERM=xterm-256color, COLORTERM=truecolor)
• Shell: /opt/homebrew/bin/bash
• Install/channel: release, Homebrew formula opencode from homebrew-core
• Active plugins: None found in config

Reproduction

1. brew install opencode (the homebrew-core formula, not the opencode-beta/opencode-v2 tap)
2. which opencode → /opt/homebrew/bin/opencode
3. readlink /opt/homebrew/bin/opencode → ../Cellar/opencode/2.0.20/bin/opencode
4. Run opencode upgrade, or /update inside the TUI

Expected Behavior

Detection returns brew and the upgrade runs brew upgrade opencode.

Actual Behavior

CLI:

Could not detect the installation method. Pass --method to choose how to upgrade OpenCode.

TUI /update:

update skipped: installation method not found
Installation method not found

opencode upgrade --method brew works, so only auto-detection is broken.

Additional Context

The Homebrew branch of the detector only matches two tap names:

const p = await fs.realpath(process.execPath)
if (["opencode-beta", "opencode-v2"].some(v => p.includes(`${path.sep}Cellar${path.sep}${v}${path.sep}`)))
  return "brew"
if (!packageName) return // → undefined → "installation method not found"

The homebrew-core formula installs to a third path that is not covered:

/opt/homebrew/Cellar/opencode/2.0.20/bin/opencode
                      ^^^^^^^^^^^ not matched

/Cellar/opencode/<version>/ matches neither opencode-beta nor opencode-v2, so the check falls through. The subsequent npm/pnpm/bun/yarn/vp probes never run because packageName is only derived from a neighbouring package.json, which does not exist for a standalone Homebrew binary — so the detector returns undefined.

Suggested fix: also match ${path.sep}Cellar${path.sep}opencode${path.sep}, or derive brew from brew --prefix opencode / a HOMEBREW_PREFIX env check.

Reproducible every time on this machine. Workaround: run opencode upgrade --method brew from a terminal (/update in the TUI has no --method option).