Strengthen the two hs.4-shipped RC-stats E2E assertions back to the
plan-original `live == 0` + `allocs == frees` invariants:
- int_to_str_drop_balances_rc_stats: `let s = int_to_str(42) in
do io/print_str(s)` allocates a heap-Str (allocs=1) but the let-arm
dec at scope close does not fire (frees=0, live=1).
- str_field_in_adt_drops_heap_str_correctly: `Box(int_to_str(42))`
pattern-matched and printed allocates the ADT cell + the heap-Str
slab (allocs=2). The match-arm pattern walk calls
field_drop_call's Str arm on the extracted field (frees=1), but
the outer ADT cell's let-binder is not trackable (frees=1, live=1).
Root cause is the effect-op arg-mode gap surfaced during hs.4: the
uniqueness analyser at uniqueness.rs:289-292 walks every Term::Do arg
in Position::Consume, gating off the let-arm dec at lib.rs:1440
(consume_count == 0 required). EffectOpSig has no param_modes field
to override the Consume-by-default walk. The fix is structural and
queued as the next iter.
These tests were shipped GREEN in hs.4 (134441b) with weakened
`allocs >= N` asserts; that was a fixture-adapted-to-bug anti-pattern.
Asserts restored to the language invariant; tests now RED, locking
in the fix obligation.
Brummel
592d87bf11