Scope

viv covers the Composer commands you run every day. Everything else stays with Composer, and the composer shim passes those commands through.

Commands viv runs itself, with the same output as Composer:

Start and resolve: init, new (create-project), install, update, update-lock, add (require), rm (remove), dump-autoload, normalize.
Inspect: show, tree, why, outdated, audit, validate.
Maintain: lock (convert, merge, export), workspace (list, init, add).
Run: run, exec, php (install, list), the lifecycle scripts, and the cache commands.
diagnose prints viv's own report, not Composer's.
isolate prefixes a plugin's bundled libraries with php-scoper, which Composer has no command for, and completions prints a bash, zsh or fish completion script.

Commands that stay with Composer: search, config, global, self-update, licenses, depends and the rest.

Works with

Repositories: Packagist, Private Packagist and Satis, including a local file:// mirror, path, vcs, git, GitHub and package (inline declarations) sources; redirects are followed.
Packages: zip and tar dists, a git checkout when there is no dist, preferred-install: source, sha1 checks, credentials from auth.json and COMPOSER_AUTH.
Autoload: PSR-4, PSR-0, classmap and files; --optimize-autoloader and --classmap-authoritative; platform_check.php; vendor/bin proxies; lifecycle scripts.
Commands: install, full and partial update including --minimal-changes and Composer's default blocking of versions with a security advisory (--no-blocking to allow them), add, rm, dump-autoload, and offline mode with --offline or COMPOSER_DISABLE_NETWORK. install refuses before writing anything when the lock needs a PHP version, extension or library the detected platform lacks, honouring config.platform, --ignore-platform-reqs and --ignore-platform-req.
Plugins: the ones with native adapters, listed under Plugins.