fix(learn): fixed-side negatives only where the fixed side declares the function

A pair now gives a fixed-side negative only when the fixed side's source declares the
labelled function (the excerpt builder's matcher; a name on a code line where the matcher
resolves neither side), or when a deterministic rename at a distinct fix commit replaces it
(one new function, same parameter list, changed body: provenance fixed_side_moved). Anything
else is counted under pair_fixed_side.absent_fixed_side, not labelled.

108 pair labels lose their negative: 80 seeded pointer pairs whose fixed side is a guard
helper of the same commit, and 28 Real-Vuln-Benchmark traps whose fixed side is a sibling
handler of the same snapshot (4 of those handlers are labelled positives themselves). The
memory build no longer substitutes the catalog's fix_function on the fixed side. The pair
cache is an allowed label-source tree so pointer sides are read through the guard.

Snapshot: benchmarks/measurements/2026-10-01-decision-engine-labels (counts only).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/learn/cli.py

@@ -211,7 +211,6 @@ def _memory_build(args: argparse.Namespace) -> int:
     try:
         build = build_examples(
             labels, records_by_key(rows), reader, sources=sources, store=store, profile=args.profile, license_of=reader.license,
-            function_of=reader.function,
         )  # fmt: skip
     except ExampleBuildError as exc:
         print(f"learn memory build: {exc}", file=sys.stderr)