Cask upgrade fails: `It seems there is already an App at '/Applications/X.app'`

Symptom: bootstrap.sh upgrade reports Some greedy cask upgrades failed, and brew upgrade --cask --greedy ends with Error: Problems with multiple casks: naming an app (or a binary, e.g. already a Binary at '/opt/homebrew/bin/dnx'). Homebrew reverts the upgrade, so the same failure repeats every run.

Root cause: Homebrew refuses to overwrite an artifact it doesn’t have a receipt for. Two ways an auto-updating cask gets there:

Upstream renames the app bundle. The cask’s app stanza changes name, the self-updater has already written the new bundle, and brew’s receipt still points at the old one — so brew tries to create a file that exists. This is what codex-app did: OpenAI folded the Codex desktop app into ChatGPT and renamed Codex.app → ChatGPT.app (same com.openai.codex bundle ID). The codex-app cask is deprecated with chatgpt as its replacement, and the auto-migration leaves an orphan Caskroom/codex-app/ directory behind, so brew list --cask still shows it while brew info says “Not installed”.
A leftover symlink from a previous install. dnx pointing into /usr/local/share/dotnet/ blocked every dotnet-sdk upgrade.

Confirm:

1
brew outdated --cask --greedy               # which casks are stuck
2
ls /opt/homebrew/Caskroom/<cask>            # receipt version vs the running app
3
/usr/libexec/PlistBuddy -c "Print :CFBundleIdentifier" /Applications/X.app

Two apps printing the same bundle ID means one is a stale copy under the old name, not a second product.

Fix: brew install --cask <name> --force — it overwrites the unmanaged artifact, removes the old-named bundle, and re-establishes the receipt at the current version. Delete any orphan Caskroom/<old-cask>/ directory (it holds only a symlink and metadata; rm -rf on it does not follow the symlink) and remove stray binaries before retrying. For a renamed cask, also update packages/Brewfile to the replacement name.