After Your First Contract

Your First Contract ends with two parties, one signature rule, and a witness that lets either of them sign. The pages below are what you do next. Each one adds one idea and one use case, and each one ends on a commit you cause to be refused.

Read them in order. Each page starts its own directory, so a mistake on an earlier page does not block the next one. When a page shows a modality block, that block is the file model/default.modality. Replace the file with it before the commit that follows. Formulas come from the formula cookbook. Models come from the model cookbook.

	You learn	You use it to
1. The commit that used to work	A rule stays	Freeze a note the parties already posted
2. States, not one room	A commit has to be a step	Accept an offer only after it is made
3. A move that never happens	A box: every matching step	Let members write, and membership change only together
4. A finish that stays possible	Reachability	Keep a way to mark the offer done
5. The rule that looks right	A box and a diamond	Require a memo before an invoice changes
6. A key, not a person's name	Who signs is a posted key	Take turns
7. Two of three	A threshold	Move a treasury
8. Pay someone	Create, send, receive	Pay an invoice
9. Too strong, then too weak	A rule can miss the request	Break a membership rule both ways, then repair it
10. On the testnet	A sequenced commit	Let a stranger open the contract
11. Get paid	A wallet is a contract	Receive and send MOD
12. Someone else's word	A fact has to be posted	Release an escrow after delivery is attested
13. Their state, in yours	A repost is a snapshot	Bind to a price they already posted
14. Commit, then show	A hash, then the body	Seal terms, then open them
15. The program and the invariant	A program computes	Swap, inside the pool's rules
16. An agent may edit, and may not land	The rule binds the tool	Land a change only on the path
17. Hand it over	Replay	Check a log you did not write

Contract Hub, hub assets, and the JavaScript SDK are how you do the testnet and repost lessons with another person or from code.