Brummel
b5b0c2d7dc
Single iter closes the milestone: language rule at three check-time sites (uniqueness.rs + linearity.rs + linearity.rs doc-comment), four lockstep ret_mode-Own edits (builtins.rs + synth.rs for int_to_str and float_to_str), one Str carve-out in drop_symbol_for_binder's App arm, RED→GREEN verification of the two existing pinning tests, two new positive tests (Int-arg primitive non-leak, repeated Str-arg borrow), DESIGN.md anchor under Decision 10 covering BOTH arg-position rules (Ctor=Consume, Do=Borrow), WhatsNew entry, roadmap close of the heap-Str ABI P1 milestone. Plan-recon DONE: lint-side-effect surface (over-strict-mode on (own T) params used solely via effect-ops) is empty for the current corpus, so no follow-up sweep iter needed. IR-snapshot regen confirmed no-op. Two inline IR-shape tests at codegen/src/lib.rs:4127-4205 stay green (ret_mode flip does not change their emitted-call assertions).