[timfennis]

Groundwork for making Any explicit (#331): these built-ins gave Any that nobody wrote, which would need a cast at every use once Any only comes out through as.

• panic(message) stops the program with the message and has type Never, so it can end a branch whose other branches give a value: if c { 1 } else { panic("no such thing") } is an Int. assert(false) can't do this, as assert returns when its condition holds.
• combinations(xs, k) and permutations(xs, k) now give lists rather than tuples, as k is only known when the program runs: Iterator<List<T>> and List<List<T>> instead of Any. Destructuring them works as before; they print as [1,2] rather than (1,2). On the advent-of-brian day 8 solution, nothing in the pair loop is picked as the program runs any more, which made part 2 about a third faster.
• find_subsequence returned the index or (), typed Any. It now returns an Int and fails when the subsequence isn't there, and the new find_subsequence? returns an Option<Int>, like first/first?. An empty subsequence is found at 0 instead of panicking.

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[chatgpt-codex-connector]

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-13T21:12:40.272815Z	84f7d9a	PR opened

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