🤖 AGENTS.md: todo-spinel

The one rule: this app is Ruby compiled ahead of time, and nothing else runs in production. Everything the server does is written in the Spinel-compilable subset of Ruby (app.rb, via tep) or in the small C shims tep already ships. No Ruby interpreter, no shared library beyond libc, no client framework, no JS build step.

Tenancy

• One instance for the whole app. A single process and a single SQLite file (--db) serve every visitor.
• Each visitor's list is kept separately by an anonymous cookie. The first visit sets tid=<22 base64url characters> (128 bits from the kernel's getrandom), HttpOnly; SameSite=Lax; Path=/, plus Secure over https. Every query is scoped by that value; an id from someone else's list is a 404. The visitors table holds every token the server has issued; any other cookie value is replaced with a fresh one.
• No sign-in. There are no accounts, passwords or e-mail addresses.
• Trust class C. Todo text is stored as plain text in SQLite. That's a deliberate choice for a demo app: nothing in it is meant to be secret, and the platform's at-rest protection of the database is the only protection it gets.

Working here

• Work only in apps/spinel/. BRIEF.md and CONTRACT.md at the repo root are binding.
• The toolchain checkouts (spinel, tep, spinelkit) are read-only. The Makefile copies tep into .cache/ and applies patches/*.patch there.
• Servers bind 127.0.0.1 only. Scratch goes in $TMPDIR. No sudo.