Mastodon on Spinel

The goal has a two-part success condition: Mastodon — a real, large, heavily-deployed Rails application — passes its own test suite when compiled by Spinel, and the build step earns the status of a supported configuration. That second half deserves precision. Mastodon is deployed widely, and it isn't important that all Mastodon deployments run on the same runtime. But "supported configuration" is a deliberately higher bar than where JRuby and TruffleRuby sit today — "it might work, but is unsupported" — which is precisely why no operator bets production on them. Supported means checkable artifacts: a CI job in the matrix, a documented deployment option, issues that get triaged rather than closed as "unsupported runtime." It's a bar someone else decides you've cleared, so the deadline — end of 2026 — binds what's mine to control: the suite passing, the evidence assembled, the ask credibly made. Behind the headline sits the project's real question, unchanged since the beginning: how much of Rails transpiles, honestly accounted, with a per-target ledger of what doesn't rather than a demo reel of what does. .