Brummel
3113258680
Resolves the architect's drift report on the 18g sub-arc: - DESIGN.md: ratify mode-metadata's codegen role. param_modes / ret_mode were already on Type::Fn since 18a; with 18d.4 / 18g they became load-bearing for drop-emission decisions in codegen. The new 'Mode metadata is load-bearing for codegen' subsection records the four seams (Iter A + Iter B + 18g.1 + 18g.2) and names the let-alias-of-borrow carve-out the gates do not propagate through. - bench/run.sh: post-throughput, invoke bench/latency_harness.py on the three canonical arms (Implicit @ gc, explicit @ rc, Implicit @ rc control). The Boehm-retirement bench numbers are now reproducible by anyone running the harness, not just by hand on a specific host. - Negative coverage: examples/rc_let_implicit_returning_app + alloc_rc_let_binder_for_implicit_returning_app_does_not_drop pin the asymmetry to the (own)-ret-mode test (live=0 there, live=1 here). The Borrow-ret-mode case is covered by the language design itself — typechecker rejects 'borrow- passthrough' shapes with consume-while-borrowed. JOURNAL entry records four items as deferred known debt: emit_inlined_partial_drop dynamic-tag fallback, carve-out diagnostics surface, bench-number stat-of-N, and the cross-family ordering observation about CLAUDE.md's tidy-iter rule. The 18-arc is formally closed with this tidy. Next iter is the orchestrator's Boehm-retirement decision (Path A vs Path B from JOURNAL 2026-05-08 18f entry, joined by the post-18g.2 re-bench numbers).