1. What cost the most: learning the AST and walker API that Nikaia tools code uses. That took about six read turns: the Stmt, Expr, FnArg and BinaryOp shapes, id_of, the check_visit_* helpers, written_expression, and the fact that the interner is parsed.interner. After that, one Rust borrow conflict cost a rewrite before the first build: calling self.blocked_* inside the visit_stmt closure clashed with self.seen. The build cycle went through on the first try.
2. What the brief could have handed me:
   • That tools/check_visit.nika (check_visit_preorder, check_visit_stmt, check_visit_stmt_blocks) is the walker to reuse.
   • That id_of in ast.nika gives a node’s id.
   • That written_expression(words, e) prints an expression as written, and Rust passes the interner as &parsed.interner.
   • That bounds_basic.nika already shows a similar per-statement binding walk (statement_says, any_symbol).
   • Which it modules run --bounds; I found them with a grep.
3. Checks run:
   • Each paid off: one lower-std, build, lower-std cycle; the brief’s probe with check --bounds; lower-std --bounds with proved.nika; seven it modules (65 tests); cargo fmt; clippy on 1.97 and on 1.99.1 (installed, cold build in a separate target dir, then deleted); pre-push-check.sh, then the badge.
   • Wasted: cargo test --lib bounds_report:: (0 tests exist), and the grep of three it files that matched only on the word “checked: “.
   • The 1.99.1 clippy was the most expensive check. It was needed only because of the toolchain gap, and found nothing.
4. One change that would save the most: a builder-facts entry, “Walking a body in tools/*.nika”, listing those helpers (check_visit_*, id_of, written_expression, words.resolve) with a five-line example. Also, a brief that adds parameters to a Nikaia function called from Rust could say “build a small Copy context struct before the closure”, which would avoid the borrow trap.
   • Second: preinstall CI’s stable toolchain with clippy on the machine, so no builder pays for the cold 1.99.1 build.

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