[Elieser007]

Summary

• Fixes the shell install steps (fish/zsh/nushell) on Arch/Fedora/Debian when a package is not available in the native package manager repositories.
• The installer now checks per-package availability against the native manager (pacman -Si / dnf info / apt-cache show) before running the install transaction, which previously aborted entirely when a single package was unknown.
• Packages the native manager cannot provide are installed from GitHub instead: carapace (binary from carapace-bin releases, verified against the official asset digest from the GitHub API — the same SHA256 the project publishes in its checksums.txt) and zsh-theme-powerlevel10k (cloned to /usr/share/powerlevel10k, a path the bundled .zshrc already sources).

Motivation

On vanilla Arch and Fedora, carapace is not in the official repositories, and zsh-theme-powerlevel10k is only present in some repositories (e.g. CachyOS). Running pacman -S --needed --noconfirm fish carapace zoxide atuin starship fails entirely with error: no se ha encontrado el paquete: carapace, aborting the whole shell install step.

The runtime availability check means distros that DO provide the packages (CachyOS provides zsh-theme-powerlevel10k) install them natively; others fall back to GitHub — no hardcoding per distro and no AUR helper dependency.

Changes

File	Change
installer/internal/tui/installer.go	Add GitHub field to platformPackages; per-package availability check (packageAvailableInRepo) with graceful degrade to the native manager; installNativeWithGitHubFallback; installCarapaceBinary (latest release resolved via GitHub API, verified against the official digest); installPowerlevel10k; tar.gz binary extraction helper.
installer/internal/tui/platform_packages_test.go	Mocks now model the real system.Run contract; tests for missing→GitHub, CachyOS-style native p10k, infra degrade, apt quirks, missing-without-fallback error, and brew fallback.

Test Plan

• go build ./... passes
• go vet ./... passes
• go test ./installer/... -skip 'Golden' passes (TestOSSelectGolden is a pre-existing environmental failure on Linux — the golden was generated on macOS; it fails on main without this change too)
• End-to-end: carapace asset download + digest verification against the official GitHub API digest
• Manual validation on real CachyOS: fish step installs carapace from GitHub and the zsh step installs zsh-theme-powerlevel10k natively from the cachyos repo; installer completes successfully