# iter eob.1 — Effect-op args walked as Borrow; heap-Str RC discipline closes

**Date:** 2026-05-12
**Started from:** b5b0c2d7dcd8bec1819801257de7731edc542e0f
**Status:** DONE
**Tasks completed:** 7 of 7

## Summary

Land the language rule that `Term::Do.args[*]` are walked in
`Position::Borrow` by the uniqueness and linearity passes, plus the
two heap-Str-specific shape fixes (`ret_mode: Own` for `int_to_str`
/ `float_to_str`; Str carve-out in the App arm of
`drop_symbol_for_binder`) that make the existing RED tests at
`crates/ail/tests/e2e.rs` flip to GREEN under `--alloc=rc`. Both
arg-position rules (Ctor = Consume, Do = Borrow) are anchored in
DESIGN.md §Decision 10. The heap-str-abi milestone closes here:
WhatsNew entry shipped, roadmap P1 entry checked off, downstream
Post-22-Prelude `depends on:` line removed.

The five plan layers landed first-shot in lockstep — no review
re-loops fired on any of the 7 tasks. The pre-existing RED tests
(`int_to_str_drop_balances_rc_stats`,
`str_field_in_adt_drops_heap_str_correctly`) flipped to GREEN with
the predicted concrete numbers (`allocs == 1, frees == 1, live == 0`
and `allocs == 2, frees == 2, live == 0`). Two new positive tests
pin the rule's coverage at the primitive boundary (Int through
`io/print_int`: zero RC traffic) and at the linearity boundary
(heap-Str through two sequential `io/print_str` calls: allocs == 1,
frees == 1, live == 0). Workspace test --workspace + cross_lang.py
+ compile_check.py all green. check.py shows the same noisy
latency-max + bump_s cluster the audit-cma and audit-ms journals
both left pristine ("not coupled to milestone, baseline left
untouched for second consecutive audit") — same precedent applies
here; baseline left as-is.

## Per-task notes

- iter eob.1.1: Term::Do arg-walks flip Consume → Borrow in both
  uniqueness.rs:289 and linearity.rs:506; linearity.rs:42 doc
  comment split into two bullets matching the new code shape.
  Inline clarifying comment added on the linearity-side flip
  mirroring the Ctor-arm convention. cargo build + workspace
  check-crate tests green.
- iter eob.1.2: builtins.rs `float_to_str` (:200) + `int_to_str`
  (:210) and synth.rs `float_to_str` (:172) + `int_to_str` (:179)
  all flip `ret_mode: Implicit` → `ret_mode: Own` in lockstep.
  Workspace build clean. Target test now reports the predicted
  link-error shape "undefined value @drop_int_to_str_drop_rc_Str"
  — exactly the gap Task 3 closes.
- iter eob.1.3: drop.rs App arm of `drop_symbol_for_binder` gets
  the Str carve-out `if name == "Str" return ailang_rc_dec`,
  symmetric to `field_drop_call`'s existing Str arm. The
  comment block mirrors `field_drop_call`'s wording. cargo build
  clean.
- iter eob.1.4 (observational): both RED tests flip to GREEN with
  the predicted concrete numbers (allocs == 1, frees == 1 / allocs
  == 2, frees == 2; live == 0 on both). Full e2e suite (79 tests)
  all green — no other fixture's RC trace shifted unexpectedly.
- iter eob.1.5: two new fixtures
  (`examples/int_to_print_int_borrow.ail.json`,
  `examples/heap_str_repeated_print_borrow.ail.json`) + two new
  e2e tests (`int_arg_to_effect_op_does_not_rc_track`,
  `heap_str_repeated_print_balances_rc_stats`) appended near
  e2e.rs:2625. Both new tests PASS first-shot with exact predicted
  RC stats.
- iter eob.1.6: DESIGN.md §Decision 10 gets a new subsection
  `#### Arg-position policy for compound AST nodes` after the
  `ret_mode` block. The two arg-position rules (Ctor = Consume,
  Do = Borrow) are anchored together as language rules, not
  per-op annotations. One added linking paragraph explains how
  the Do = Borrow rule cooperates with the `ret_mode == Own`
  letbinder-trackability rule above to balance heap-Str RC
  discipline — within the plan's "Boss judgement on placement"
  carve-out.
- iter eob.1.7: WhatsNew.md entry appended at bottom (user-facing
  wording, no internals). roadmap.md heap-Str ABI entry flipped
  `[ ]` → `[x]`. Post-22 Prelude `depends on:` line removed (the
  only dep was Heap-Str, which has shipped). cargo test workspace
  + cross_lang.py + compile_check.py all green. check.py noisy
  latency cluster left pristine per audit-cma/audit-ms precedent.

## Concerns

(none — all 7 tasks DONE without review re-loops)

## Known debt

- check.py shows recurring noisy `latency.implicit_at_rc.max_us`
  / `latency.explicit_at_rc.max_us` tail-jitter, plus
  `throughput.bench_list_sum.bump_s` swinging +11-15% across
  back-to-back runs (with reciprocal `gc_over_bump` improvement
  on the same fixture). Neither family is reachable from this
  iter's changes (bump_s on bench_list_sum has no effect-ops; the
  list-sum hot path has no int_to_str / float_to_str calls). The
  audit-cma and audit-ms journals already document the same
  noise cluster as "not coupled to milestone, baseline left
  pristine for two consecutive audits" — same precedent applies;
  baseline untouched.

## Files touched

Code:
- crates/ailang-check/src/uniqueness.rs (Term::Do Consume → Borrow)
- crates/ailang-check/src/linearity.rs (Term::Do Consume → Borrow + doc-block split)
- crates/ailang-check/src/builtins.rs (int_to_str / float_to_str ret_mode → Own)
- crates/ailang-codegen/src/synth.rs (int_to_str / float_to_str ret_mode → Own)
- crates/ailang-codegen/src/drop.rs (App-arm Str carve-out)

Tests + fixtures:
- crates/ail/tests/e2e.rs (2 new positive tests appended)
- examples/int_to_print_int_borrow.ail.json (new)
- examples/heap_str_repeated_print_borrow.ail.json (new)

Docs:
- docs/DESIGN.md (Decision 10: arg-position policy subsection)
- docs/WhatsNew.md (heap-str-abi milestone close entry)
- docs/roadmap.md (Heap-Str ABI P1 closed; Post-22 Prelude
  depends-on line removed)

## Stats

bench/orchestrator-stats/2026-05-12-iter-eob.1.json
