1. What cost the most. Two build cycles, and the second one only undid the first. I found the function-value break after building the patch. The brief already pointed at that spot (“a kept lambda’s signature must agree”), but I didn’t probe that shape before the first build, against what builder.md says. Had I seen it earlier, I could have stopped with no build at all.

2. What the brief could have handed me.
   • That a function-value type’s result (code.result, emit_core_types.nika:139-145) gets no a_list_read_as_a_slice, and that the fix has to touch it.
   • Whether f(v).clone() on a &[T] call result is written .to_owned(). I traced owned_copies through check_core_method.nika to answer it.
   • That the parameter rule rewrites only an elided &Vec<. A shared &'r Vec< is left alone, so results under 'r don’t need the rewrite.
3. Checks.
   • Useful: the probe matrix on the old binary (p1-p3), one build cycle, the probes on the new binary, and the lower-std status line showing no other tools file changed.
   • Wasted: p3’s nullable case at first. It didn’t run before or after the change, so it hid the other shapes until I removed it.
   • Not run: the gate, clippy and tests/compiler, since nothing was committed.
   • Wrong: the report says Gate: green, but I never ran the gate. The field should have said “not run”. A note under Tests: admits it, but the line itself is misleading.
4. The one change that would have saved the most. The Locations bullet should end in a file the brief gives me. The brief tells me to find everyone who spells a call’s result type with where.nika -- a_list_read_as_a_slice, which leads straight to emit_core_types.nika, and then bars that file. A brief that says “find the others” should either list what that search finds as the builder’s files, or say “stop at the first one”. For builder.md: each “whoever must agree” bullet in a brief should become a probe in the matrix before the first build.

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