[mikemaccana]

The book taught checks-effects-interactions as protection against a token hook, or an upgraded callee, re-entering a program mid-transfer and double-withdrawing. On Solana that call can't happen. solana-program-runtime returns InstructionError::ReentrancyNotAllowed when a program already on the call stack is invoked by anything other than itself. A failed call also undoes the whole transaction. So the order in which a handler writes its own state and calls other programs doesn't open an attack.

This follows quicknode/solana-program-examples#189, which removes the same claim from the companion programs' comments and READMEs.

After this merges, the book's prose, glossary and figures no longer mention checks-effects-interactions. The only remaining mentions are the example sentences in the comment on the lint rule in scripts/lint-manuscript.mjs, which quote the old wording to show what the rule rejects.

Changes

• The Adversary: the paragraph that taught the rule now states the runtime's re-entry rule and the transaction's atomicity, then introduces the three boundary checks that do matter (validate what a CPI returns, re-read what a CPI changed, assume the instructions after yours are hostile). "follow the same rule" → "do this". In the checklist, "Apply checks-effects-interactions at every boundary" → "Make every invariant hold at the end of your own instruction".
• Order Book: the settle_funds() paragraph says what the handler does: it zeroes the counters and pays out the snapshot, so a user who calls settle_funds() again is paid nothing, and a failed transfer undoes the zeroing. The summary bullet says the same.
• Fundraiser: removed the checks-effects-interactions sentence. The double-refund explanation (the receipt is closed) stays.
• Managed Fund: removed the "(checks-effects-interactions, as in every chapter)" aside.
• Betting Market: "Two orderings in this handler close attacks", with its re-entry bullet, is now one paragraph: the claim removes the bet from the index and closes the account, and the closed account stops a double claim (test_double_claim_fails).
• Options: "Then the effects come before the transfer" → "Then, before the transfer, the handler makes these changes in order".
• Perpetual Futures: removed checks-effects-interactions from the summary's list of concepts already covered.
• Glossary: removed the checks-effects-interactions entry. Nothing linked to it.
• Figures: in order-book-settle.svg, the caption "checks-effects-interactions, so a re-entrant caller finds nothing left" → "the handler zeroes the counters and pays out what they held, so a user who settles again is paid nothing". In betting-alice-claim.svg, removed the "effects before interactions" label and "first" from "1. index entry removed first".

Checks

npm run lint, node scripts/check-figure-geometry.mjs and npm run build-pdf pass. Both changed figures were rendered and checked by eye.

This branch was reset to main after #243 merged. A commit had been pushed to it after that merge, and it now sits on top of main here.

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https://claude.ai/code/session_014pXG1pw56BE99p4A8qmrQk