AILang/docs/journals/2026-05-12-audit-23.md

audit-23 — Milestone 23 close

Date: 2026-05-12 Started from: 3fed372 Status: DONE — milestone 23 closed (1 ratify + 1 nit-fix) Skill: audit (architect + bencher)

Summary

Milestone-close audit for Milestone 23 (Eq/Ord prelude). Architect clean on substance — all 8 acceptance criteria of docs/specs/2026-05-11-23-eq-ord-prelude.md met, no out-of-scope creep, DESIGN.md two-arm-fixpoint description (line 1513-1556) matches mono.rs::collect_mono_targets observable behaviour, roadmap split internally consistent. Bencher found and ratified one structural compile-time shift; the iter-23.5 journal's "one sub-ms noise-band metric" framing was wrong on both counts (4 metrics, not 1; consistent +18-20% cohort shift, not noise).

Architect — drift items

• [important] docs/DESIGN.md:1692-1693 — sentence collision: "Milestone 22 ships no built-in Prelude classes. The original An earlier draft committed to …". Pre-existing since commit 613d4d8 (2026-05-10, design-md-consolidation 1.4 fixup) which edited 22a draft → An earlier draft and left the dangling fragment The original on the previous line. NOT introduced in iter 23.5; architect's attribution corrected. Boss-fixed inline: the dangling fragment removed.
• [minor] crates/ailang-check/src/lib.rs:884-894 — workspace- sibling linearity construction is O(N²) over module count. Bounded for today's 2-module workspace; named here so a future Nx-module workspace doesn't re-discover it. Bencher confirmed below that the iter-23.5 H1 cost is negligible at N=2. No action.
• [minor] crates/ailang-check/src/mono.rs:703-712 — contains_rigid_var discriminates rigid vs. metavar by Type::Var.name.starts_with("$m"). The journal already named this as a future-fragility; a structural discriminator (separate Type::Meta variant) would be the principled fix. Carry-on; not blocking.
• [nit] crates/ailang-check/src/lib.rs:709-726 — Float-NoInstance addendum mutates d.message directly. The codebase has no with_hint / extend_message convention yet, so this isn't pre-existing drift, but the next class-specific addendum (e.g. partial-Float compare) would compound to_diagnostic into a conditional chain. Carry-on; refactor when a second addendum arrives.

Bencher — compile_check regression diagnosis

Bench-rerun at HEAD 3fed372 showed 4/12 check_ms metrics above the 25% tolerance, with all 12 metrics in the +7 to +45% band — a coherent cohort shift, not the journal-claimed "one sub-ms noise metric".

Two hypotheses tested via 5-run medians over 60 samples each across four states (23.4 HEAD, 23.5 HEAD, 23.4 checker + 23.5 prelude, 23.5 checker + 23.4 prelude):

• H1 (linearity workspace-visibility + contains_rigid_var): refuted. 23.5-checker + 23.4-prelude returns to baseline noise (median +1.84% vs. baseline noise floor).
• H2 (5 new polymorphic prelude Def::Fn bodies cost real typecheck work): confirmed. 23.4-checker + 23.5-prelude reproduces the full HEAD regression (median +18.62% vs. HEAD's +18.74%; gap bounds the H1 interaction at <1%).

Cost source: each workspace check now typechecks 5 additional polymorphic Def::Fns (each carrying forall + 1 class constraint

• a match or small not (eq …) body) plus their constraint resolution. ~0.2-0.3ms median additional work per ail check subprocess; the ~5-10ms subprocess-spawn floor inflates the relative-percent figure.

Verdict: Ratify. The regression is the user-visible feature iter 23.5 shipped — five prelude helpers — accurately surfacing in the bench as "typecheck does more work because the prelude has more work to do".

Resolution

• Ratify path applied: python3 bench/compile_check.py --update-baseline re-measured (1 run, default 5 samples) and wrote bench/baseline_compile.json with the new check_ms numbers. Post-update rerun: 0/24 regressed, 0/24 improved beyond tolerance.
• Important-drift fix applied: the dangling The original fragment removed from docs/DESIGN.md:1692. One-line tidy edit; no behavioural change.
• Minor / nit drift items: carry-on. Linearity O(N²) is observed-not-blocking; mono name-prefix discriminator is journal- flagged; NoInstance addendum mutation pattern revisit when a second class-specific addendum arrives.

Concerns

• The iter-23.5 journal's bench framing was incorrect. The implementer asserted "one sub-ms metric, two others stayed inside on rerun" — fresh-rerun showed 4 above tolerance with consistent cohort shift. Implementer-phase bench rerun count was likely too small to see the cohort; orchestrator-audit pattern of running bench 5× back-to-back at milestone close is the correct granularity, and the 1-sample bench-check inside implement is not.
• Implication for future iters: when compile_check.py exits 1 during implement, the implementer should NOT classify it as noise-band without doing the same multi-run, multi-state isolation the bencher did here. Defer to audit if the framing is uncertain. This is a soft convention — encoding it as a hard skill rule would slow implement when the regression genuinely is noise; the weaker form is "if bench exits 1, the journal Concerns must describe what additional evidence was gathered, not just give a hypothesis".

Known debt

• DESIGN.md sentence-collision had been on main for two days unnoticed. No drift-review ran between 613d4d8 (2026-05-10) and this audit (2026-05-12); the implement-skill diff scope (per-iter, narrow) does not catch unrelated pre-existing fragments. Acceptable: drift-review at milestone close is exactly the catch mechanism, and it caught it.

Files touched

• bench/baseline_compile.json — re-measured baseline; numbers reflect new prelude cost.
• docs/DESIGN.md:1692 — dangling fragment removed.
• docs/journals/2026-05-12-audit-23.md (this file).
• docs/journals/INDEX.md — append (Boss-side).

Stats

No stats file — audit is a Boss-direct skill, not an implement-orchestrator dispatch.