6b3ff3bbed
First half of the post-18-arc tidy-iter (per the new CLAUDE.md iter-cycle rule). Architect's drift review flagged module-doc headers describing 18b's leak-everything snapshot or 18c.x's "deferred" debt that has since shipped. Doc-only changes; cargo build clean, cargo test --workspace green at e2e=61, no behavioural change. - runtime/rc.c top-of-file header: rewrote from "Iter 18b deliberately stops at the layout and the alloc... programs leak every allocation" (false post-18c.3) to a stage summary spanning 18b–18e. Fixed `--memory=rc` reference (renamed to `--alloc=rc` in 18b's CLI work). Updated ailang_rc_inc / ailang_rc_dec block comments to point at `drop_<m>_<T>` and the worklist as the cascade owners, not at "18c will wire this up". - ailang-check uniqueness.rs module-doc: replaced the "deferred to later iters" block (which named 18c.4 + 18d as future work, both shipped) with a current "what this pass does NOT do" block. Cross-fn reasoning is still genuinely deferred; per-type drop fns and recursive cascades are NOT this pass's job by design (codegen does them, not the inference). - ailang-codegen emit_drop_fn_for_type doc + in-body comment: rewrote "Iter 18e replaces the recursive call with an iterative worklist free" to describe the actual shipped behaviour — the 18e (drop-iterative) annotation routes annotated types through emit_iterative_drop_fn_for_type; unannotated types stay recursive by orchestrator design (cheaper IR, no worklist alloc). Held back for the second half of the tidy-iter (pending the ailang-bencher determinism result): - DESIGN.md Decision 10 line 700 says modes are "mandatory" but lines 940–952 admit they're opt-in with deferred mandatoriness. The bench result either supports tightening the mandatoriness claim or backs down to "opt-in with performance benefit" — orchestrator-level decision blocked on the bench data. - Dynamic-tag partial-drop debt is captured in JOURNAL but should be surfaced in DESIGN as a known precision gap.