bootstrap packages: tap casks using the appdir DSL fail metadata evaluation

[Guria]

mise bootstrap packages fails on tap casks that use the appdir DSL

brew-cask: packages from a third-party tap fail the packages phase when the cask interpolates appdir (e.g. binary "#{appdir}/..."). mise's lightweight tap-cask metadata evaluator defines binary, app, version, etc., but not appdir, so method_missing raises and — since third-party taps have no published API metadata to fall back on — evaluation hard-fails and the whole bootstrap packages phase fails.

appdir is a very common cask idiom (it's how casks reference the real /Applications path for binaries inside an app bundle), and the install-time shim already defines it (cask_shim.rb has def appdir; MISE_BREW_CASK_APPDIR; end) — it's only missing from the metadata evaluator (tap_cask_metadata.rb) and CaskFlightSteps.

Repro

A tap with this cask:

cask "demo" do
  version "1.0"
  sha256 :no_check

  url "https://example.com/demo-#{version}.dmg"
  name "demo"

  app "demo.app"
  binary "#{appdir}/demo.app/Contents/MacOS/demo", target: "demo"
end

[bootstrap.packages]
"brew-cask:<owner>/<tap>/demo" = "latest"

$ mise run bootstrap:packages
-e:298:in 'CaskMetadata#method_missing': unsupported cask metadata DSL `appdir` (RuntimeError)
	from Casks/demo.rb:8:in 'block in <main>'
mise ERROR published cask metadata was unavailable (failed to fetch Homebrew cask 'demo') and mise could not evaluate Casks/demo.rb
mise ERROR failed to evaluate Casks/demo.rb
mise ERROR sandbox-exec exited with non-zero status: exit code 1

Observed vs expected

• Observed: metadata extraction raises unsupported cask metadata DSL 'appdir', and since tap casks never have published API metadata, the packages phase errors out entirely.
• Expected: appdir resolves (as in the install shim / real Homebrew) and metadata extraction succeeds.

Notes from a real-world hit

Cask in question: umputun/apps/agterm (binary "#{appdir}/agterm.app/Contents/MacOS/agtermctl"). It also uses appdir inside postflight_steps → run (via the {{appdir}} template, which 2026.9.6 handles — #13060), so the top-level binary interpolation is the remaining blocker there.

Suggested fix: define appdir on CaskMetadata (and CaskFlightSteps for defense) in src/system/packages/brew/tap_cask_metadata.rb, mirroring cask_shim.rb's MISE_BREW_CASK_APPDIR-backed method.

Verified against 2026.9.5 and 2026.9.6 on macOS arm64; main's tap_cask_metadata.rb still lacks appdir.

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This report was prepared with AI assistance (pi coding agent), based on hands-on debugging of the failure.

[Guria]

Opened a fix: #13138 — defines appdir on CaskMetadata/CaskFlightSteps in tap_cask_metadata.rb, interpolating the relocatable $APPDIR marker (which the installer already resolves against the real, MISE_BREW_CASK_OPT_APPDIR-aware appdir) rather than baking a literal path. Verified against the umputun/apps/agterm cask from this report: metadata evaluation now succeeds and emits installer-valid artifacts.