SYM-20 Fix libcrypto canonical evaluation contract and add repo-local Codex skill

[iskindar]

Summary

• add a repo-local canonical libcrypto evaluation workflow for SYM-20
• distinguish authoritative gtBlock.pb compare from historical sidecar-union / old-binary results
• record fresh canonical baseline and optimized metrics plus caveats

What Changed

• add .codex/skills/runnable-libcrypto-canonical-eval/
• add scripts/libcrypto_bench_paths.py and scripts/validate_libcrypto_ground_truth.py
• add unit coverage for the new path resolvers and compare guards
• add docs/exp/2026-05-10-libcrypto-canonical-eval-contract.md and index it from docs/exp/topics.md
• add repo-local Symphony issue/follow-up skill scaffolding used to manage this workflow cleanly

Canonical Result

• baseline: precision=0.9523329079813952, recall=0.7765067563788988
• optimized: precision=0.9302727358917905, recall=0.7797547041527227
• verdict: recall improves slightly, precision regresses materially, so the canonical result is mixed

Validation

• python3 -m unittest tests.test_libcrypto_bench_paths tests.test_validate_libcrypto_ground_truth
• python3 scripts/libcrypto_bench_paths.py binary --must-exist
• python3 scripts/libcrypto_bench_paths.py groundtruth-pb --must-exist
• python3 scripts/libcrypto_bench_paths.py text-start
• python3 scripts/validate_libcrypto_ground_truth.py gap-audit --out-dir runs/groundtruth_validation/canonical_gap_audit
• python3 scripts/validate_libcrypto_ground_truth.py cmp --ll runs/runnable-dev-2026-0429-textstart-serial/libcrypto.so.3.entry_0x500cef80.ll --out-dir runs/groundtruth_validation/textstart_serial_cmp --examples 10
• python3 scripts/validate_libcrypto_ground_truth.py cmp --ll runs/runnable-dev-2026-0501-textstart-dynamic-reapfix/libcrypto.so.3.entry_0x500cef80.dynamic.ll --out-dir runs/groundtruth_validation/textstart_dynamic_cmp --examples 10
• python3 scripts/validate_libcrypto_ground_truth.py cmp --ll runs/validate-libcrypto-llm-agent-current/docker_exec/baseline/libcrypto.so.3.entry_0x500cf000.ll --out-dir runs/groundtruth_validation/canonical_baseline_cmp --examples 10 --allow-low-metrics

Refs SYM-20