After leg 1, a tail call wrapped in a trailing `(let ...)` / `(seq ...)`
still leaked: `arm_body_is_tail_call` matched only a direct
App/Do{tail:true} arm body, so for an MTerm::Let/Seq body the gate was
false and both pre-tail-call drops (the scrutinee-husk shallow-dec and
the leg-1 owned-param dec) were skipped — while lower_term still
descended through the wrapper and emitted the inner call as musttail.
The fix replaces the one-level match with a local recursive
`tail_position_is_tail_call` that peels through a trailing Let-body /
Seq-rhs chain to its tail-position sub-term. This is a contained fix:
the predicate feeds only the two drop-emission gates, never the
musttail-emission decision (which is independent, in lower_term off
App{tail:true}), so widening it restores the drops without changing
which calls are tail calls. The let-bound value's scope-close drop is
gated on `!block_terminated` and stays correctly skipped, so the
forwarded let binding is not double-freed.
Verified: the leg-2 pin goes green (live=0, was live=4); the leg-1 pin
stays green; full `cargo test --workspace` 0 failures, no double-free /
underflow / IR-snapshot delta; lockstep pairs untouched.
examples/series_sma.ail drops from live=8 to live=2 with unchanged
stdout (3.0 / 5.33333 / 5.66667 / 5.33333).
Not yet leak-clean: the residual live=2 is a THIRD, distinct leg — an
(own) heap param consumed on one match arm but live on a sibling
base-case (non-tail fall-through) arm is not dropped there, because the
fn-return Own-param dec gates on the per-fn AGGREGATE consume_count
(>=1 here, from the recursive arm) rather than per-arm liveness. Routed
as its own RED-first bugfix.
refs #63
Brummel
e3a9065aa7