1. What cost the most turns: three things outside the main work, which was the members lowering itself.
   • match T::kind refused Struct(_) (NK1250). I fixed it in check_core_pilot, emit_core_match and grammar_types.
   • A lowering defect: a Keep frame plus BTreeMap.get gave rustc error E0277. I avoided it by passing the value directly, and reported it under Found:.
   • Two small refusals, each costing an extra cycle: null is a reserved field name, and NK2105 (a value used after it was moved).

   Designing the helper rules (Option<Option<T>> per member, choosing the value rule by member_index, failing from an action with Cut) took several reads of the winnow-grammar backend.

2. What the brief could have handed me:
   • How a winnow-grammar action fails with a custom error: ErrMode::Cut with Diagnostics::external.
   • That rules can take value parameters and guards.
   • That grammar_types copies rules only for generic grammars, so a non-generic grammar using members needs a hook.
   • That T::kind arms refused _ parts.
   • That null cannot be an AST field name.
   • That ParseError carries only the rendered text, so the tests must print its first line.
3. Checks run:
   • The 5 new tests: they failed on the old binary and passed --both-settings on the new one.
   • All 44 *grammar* tests and the 7 other ::kind tests.
   • The lower-std fixpoint, cargo fmt, clippy and pre-push-check.sh.

   Wasted:

   • The parser:: and grammar:: unit-test runs: there are no unit tests in those modules.
   • One Struct(_) probe written with k[i64?](), which the language doesn’t accept there, so it needed a second run.

   Not done as the rules ask:

   • Clippy ran only on stable 1.97. 1.99.1 is out and was not installed.
   • The report says Gate: none because I ran no gate; the driver’s suite run decides.
4. One change that would save the most: a short Backend recipes section in the brief or builder-facts.md. It would cover:
   • how a grammar construct lowers to helper rules
   • how an action fails with a custom error
   • value-parameter rules and guards
   • when grammar_types copies a rule

   That would have saved most of the reading turns.

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