desktop-beta: Check for Updates fails — stable 2.0.1 zip has no ai.opencode.desktop.beta bundle

Summary

OpenCode Beta (ai.opencode.desktop.beta 0.0.0-beta-19425) Check for Updates finds stable 2.0.1, then fails with "Could not locate update bundle for ai.opencode.desktop.beta". The 2.0.1 arm64 zip contains OpenCode.app (ai.opencode.desktop), not the beta bundle.

Environment

• opencode version: opencode2 v0.0.0-beta-18866 (CLI); Desktop Beta 0.0.0-beta-19425
• OS: Darwin 25.6.0 arm64
• Terminal: xterm-256color
• Shell: /bin/zsh
• Install/channel: beta (/Applications/OpenCode Beta.app, bundle ai.opencode.desktop.beta)
• Active plugins: none found in config

Reproduction

1. Open OpenCode Beta 0.0.0-beta-19425 on macOS arm64
2. App menu -> Check for Updates (auto-check on launch also triggers it)
3. Update popup reports failure

Expected Behavior

Beta channel either offers a beta build containing ai.opencode.desktop.beta, or reports "up to date" instead of failing.

Actual Behavior

Updater state goes checking -> downloading -> error:
Error: Could not locate update bundle for ai.opencode.desktop.beta within file:///.../ai.opencode.desktop.beta.ShipIt/update.XXX/

Additional Context

• Updater config from main.log: channel: 'latest', allowPrerelease: false, allowDowngrade: true, currentVersion: '0.0.0-beta-19425', offered Found version 2.0.1 (url: .../2.0.1/opencode-desktop-mac-arm64.zip, ...).
• Pending zip ~/Library/Caches/@opencodedesktop-updater/pending/opencode-desktop-mac-arm64.zip top level is OpenCode.app/; its Info.plist: CFBundleIdentifier=ai.opencode.desktop, CFBundleShortVersionString=2.0.1.
• Full logs: ~/Library/Application Support/ai.opencode.desktop.beta/logs/20260912T141813/main.log (2 manual retries at 15:18:16 and 15:18:21), .../20260912T141401/main.log (failures at 15:14:14, 15:14:37 plus Cannot download differentially... Content-Type "multipart/byteranges" expected, got "application/zip").
• Reproducible consistently today (4 failures).