1. What cost the most turns:
   • The three older parser_grammar_* tests broke once the grammar called number_at, float_end and ledger.nika’s slice. I found this only in the full tests/compiler run, then fixed all three and re-ran them, which took another cycle.
   • float_end as a lowercase rule skipped whitespace before its first element, so 1.5 G was refused. That cost a debugging round.
   • The (digit | "_")* probe hit the known defect #1001 before I wrote it with alternatives.
2. What the brief could have handed me:
   • Tools files share one namespace, so a test that copies parser_grammar.nika also needs parse_numbers.nika and slice.
   • The API of parse_numbers.nika (the Number enum, number_at, float_end).
   • An action that throws gets normal priority (Diagnostics::external), while the Rust refusal used PRIO_STRUCTURAL.
   • The it filter errors:: is what runs tests/errors.
   • The test runner’s root() only works when run from the repository directory.
3. Checks I ran:
   • The bound-peek probe, then lower-std and its fixpoint.
   • it filtered on parse, grammar, span, range_spelling and shipped_ledger (163 passed), and errors:: (38 passed).
   • tests/compiler --both-settings (591 passed, 3 failed), then the 4 parser tests re-run singly.
   • clippy, cargo fmt and pre-push.
   • Partly wasted: the full tests/compiler run. Grepping for the tests that copy parser_grammar.nika would have found the 3 breakages in seconds.

4. Found in the tooling: commit.nika writes Fixes: into the message but dropped Part: #557. I put it back with git commit --amend, which changed only the message of my local, unpushed commit. I also corrected one wrong phrase in the body (“wrong character” for “offending character”).

5. One change that would save the most: the brief should list the files that copy or consume the file being changed (here the three older parser_grammar_* tests) and the new cross-file dependencies (parse_numbers.nika and slice). Alternatively, builder.md could say: before the suite, grep -l the tests that read the file you change, and run them first.

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