First implementation contact surfaced a plan defect: the
borrow-over-value reject cannot land green as a standalone pre-cutover
task. The prelude's polymorphic comparison builtins are
`(params (borrow a) …)` (eq/compare/lt/…); the mono pass
(apply_subst_to_type, subst.rs:165) specialises `a := Int/Bool/Float`
into `compare__Int(borrow Int, …)` — the language's OWN generated code
in the forbidden `(borrow value-type)` shape. The standalone check
broke compare_{int,bool}_mono_symbol_emits_branch_ladder.
Spec 0062's "value types always own" rule is universal, so generated
code must honour it too: the principled fix is a mono-pass coercion
`(borrow value-type) -> (own value-type)` (a no-op — value types carry
no RC, so own vs borrow emits no inc/dec and the branch-ladder IR is
unchanged). The check and the coercion are a matched pair and now live
together in Task 4 (Steps B1-B2), which touches the mono path anyway.
Pre-cutover green tasks are now Task 1 (borrow-return reject) + Task 3
(throwaway migration tool). Task 1's check_def destructure binds only
ret_mode (param_modes stays under `..`); Task 4 Step B2 widens it.
Spec gap to record at the next 0062 brainstorm touch: the
borrow-over-value rule needs its mono-coercion clause spelled out — the
spec tested only the authored case.
refs #55
Brummel
7dc21234f0