# AILang Roadmap Priority-ordered list of upcoming work — milestones, features, todos, and ideas. The orchestrator maintains this file. The user can request additions; the orchestrator chooses what to remove or reprioritise as work progresses. ## Conventions - One checkbox per entry. `- [ ]` is open; `- [~]` is in progress (work has started — a plan exists or commits are landing); `- [x]` is done. A finished entry may stay briefly for context, then is removed; the durable record stays in `git log`. - Each entry is tagged by **kind** and lives under a **priority** bucket: - **\[milestone\]** — big chunk that will get a `docs/specs/.md`. - **\[feature\]** — smaller addition inside a milestone, no full spec. - **\[todo\]** — concrete task that can run without a brainstorm (cleanup, doc fix, mechanical refactor, test backfill). - **\[idea\]** — not yet decision-ready, no commitment. - Optional `depends on:` line names another entry that has to land first. - Optional `context:` line points to the rationale: a spec file under `docs/specs/`, a commit hash (`git show `), or a `git log --grep=""` pointer for older entries. The roadmap is intentionally terse; rationale stays in those sources. - Priority buckets: - **P0** — in flight. Spec or plan already exists. - **P1** — next up. Decision made; not yet started. - **P2** — medium-term. Decided in principle, scheduled later. - **P3** — ideas. No commitment; may be cut. ## P0 — In flight - [x] **\[milestone\]** Remove `mut` / `var` / `assign` — CLOSED 2026-05-18. The local-mutable-state construct removed entirely and atomically (`Term::Mut`/`Term::Assign`/`MutVar`, the 3 Form-A keywords, the 4 `mut` `CheckError` variants, `mut_scope_stack`, every exhaustive `Term` arm across 17 src files) in lockstep with DESIGN.md + fixtures + drift trio + carve-out + roadmap; `loop`/ `recur` + `let`/`if` are the surviving forms. Justified by the feature-acceptance criterion applied inverted (clause 2 redundant, clause 3 IS the iterated-mutable-state bug class). Approach A: no deprecation window, JSON tags fail closed; shared codegen alloca machinery kept (loop reuses it, renamed `binder_allocas`) + the `Term::Lam` escape-guard loop half byte-equivalent. spec/plan/ iter (`d1ad50e`/`f355899`/`07f0802`), milestone-close `audit` clean (architect `[high]` form_a.md fixed in `.tidy` `4837871`; bench causally exonerated — HEAD vs pre-milestone bench binaries `cmp`-byte-identical, no ratify), `fieldtest` clean (4 fresh programs, all worked first try without mutable locals — the removal thesis empirically confirmed). Decoupled from Stateful-islands. Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-remove-mut-var-assign.md`; `docs/specs/2026-05-18-fieldtest-remove-mut-var-assign.md` - [x] **\[milestone\]** Prose `loop` binders — projection redesign — CLOSED 2026-05-18. Form-B prose now renders loop binders as a parenthesised init-list on the keyword (`loop(acc = 0, i = 1) { … }`, positionally isomorphic to `recur(...)`) instead of bare `name = init;` statements inside the body block (which misread as C/Rust re-init-every-iteration). Single-iteration, projection-only: one `ailang-prose` `write_term` `Term::Loop` arm + 2 committed byte-equality `.prose.txt` snapshots/tests; loop/recur AST, Form A, JSON-AST, typecheck, codegen, and the Form-A↔JSON round-trip invariant all byte-unchanged. brainstorm→plan→implement (`c657e74`/`6533134`/`c9355d7`); milestone-close `audit` clean (architect zero drift; bench carry-on — sole firing is the tracked P2 `*.bump_s` environmental staleness, latency-tail proven sampling noise by re-run); no fieldtest (projection-only, no authoring- surface change). Stays here briefly for context; remove once stale. - context: `docs/specs/2026-05-18-prose-loop-binders.md`; surfaced from the loop/recur prose review (2026-05-18 chat). - [x] **\[milestone\]** Standalone `loop` / `recur` — CLOSED 2026-05-18. Strictly-additive strict-iteration surface, `recur` tail-position-only, no totality claim. Shipped: iter 1 `a179ec3` (additive AST nodes), iter 2 `1566ce0` (typecheck), iter 3 `edd2558` (codegen + run-to-value E2E), tidy `39380d3`/`2ee9794` (lambda-captures-loop-binder rejected at check). Milestone-close `audit` clean (architect drift resolved, bench pristine 25/0 carry-on); `fieldtest` 2026-05-18 clean on all four milestone axes (0 bugs; diagnostics point-exact+self-fixing, recur-tail through match/let, loop-as-value-subexpr byte-stable, no-termination exact). Two orthogonal non-blocking findings routed to P2 todos (niladic `(app f)` — re-confirms mut-local F3; module `(doc)` diagnostic hint). Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-17-loop-recur.md`; `docs/specs/2026-05-18-fieldtest-loop-recur.md`; principles entry `docs/specs/2026-05-17-llm-surface-discipline.md` §6.2. - [x] **\[milestone\]** DESIGN.md / docs honesty lint — CLOSED 2026-05-18. `docs/DESIGN.md` + `docs/PROSE_ROUNDTRIP.md` now mirror ONLY the current state, present-tense: 14 DESIGN.md corrections (Wunschdenken stated-as-fact + non-citation post-mortem/doc- archaeology stripped) + the PROSE tool-use/MCP paragraph; genuine forward intent (LLM tool-use/MCP/LSP) relocated to P3. The two-pronged tense+modality discriminator is codified present-tense as a DESIGN.md `### What this document is …` meta-subsection (Approach A) the architect cites. Anti-regrowth two ways: a wrap-robust enumerated absent/present pin `crates/ailang-core/tests/docs_honesty_pin.rs` (a `norm()` whitespace-collapse helper structurally discharges the recurring grep/contains line-wrap failure family — strictly better than the effect-doc-honesty "keep-on-one-line" precedent) + wrap-robust advisory Sweep 5 in `architect_sweeps.sh` (contiguous-fragment regex) with full sweep-count lockstep + a new `ailang-architect.md` "DESIGN.md honesty drift" bullet. Procedural enumeration vindicated: the Task-4 Step-14 catch-all caught a genuine soft-wrapped extra FIX (Form-B prose-projection bullet) a frozen list + the spec's illustrative regex would both have missed. Single iter (`aff25cd`/`de66eb7`/`7580d43`); milestone-close `audit` CLEAN (architect clean, one `[medium]` advisory Sweep-5 self-match wart → P3 below; bench causally exonerated — HEAD vs `5bb7211`/`de66eb7` bench binaries `cmp`-byte-identical, NO ratify); no fieldtest (zero authoring-surface change). Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-docs-honesty-lint.md` (grounding-check PASS 10/10). ## P1 — Next - [x] **\[milestone\]** Embedding ABI — M1: linkable artifact + scalar C entrypoint + `main`-free lifecycle — CLOSED 2026-05-18. First of the five-milestone arc (M1–M5) making a compiled AILang kernel callable in-process from a concurrent Rust host. Shipped: additive `FnDef.export: Option` (hash-stable, ~85-site compile-driven thread); Form-A `(export "")` modifier (round-trip-gated); check-side scalar-only+effect-free export gate (`export-non-scalar-signature` / `export-has-effects` — the feature-acceptance clause-3 discriminator *in code*); codegen `Target::StaticLib` (suppresses `@main`+`MissingEntryMain`, emits one external `@` forwarder per export, decoupled from `ail__` mangling per Decision 2); CLI `ail build --emit=staticlib` (`lib.a` + separate `libailang_rt.a`). Coherent stop PROVEN: C host links both archives, calls the scalar kernel, typed return holds. spec `51160e9` (grounding-check PASS) → plan `b0bd7ef` (Repaired) → iter `818177d` (partial 1–3 + Boss plan Repair: a module≠stem fixture defect, resolved Option 2) + `e406d07` (DONE 4–7). Milestone-close `audit` `425c4eb` CLEAN (architect clean — Invariant 1 holds semantically, lockstep intact; sole `[low]` rustfmt-divergence evidence-adjudicated carry-on, 1137 pre-existing tree-wide divergences prove rustfmt is not a project convention; bench `check.py` exit 1 decisively causally exonerated — 21/21 bench binaries `cmp`-byte-identical vs pre-milestone, the two tracked-P2 noise families, NO ratify). `fieldtest` `6a4e866` substantiated the thesis (0 bugs; Int+Float positive E2E first-try clean = clause-1; both clause-3 rejections precise+self-correcting; 3 working) — 3 non-blocking findings routed to the two follow-up items directly below. Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-embedding-abi-m1.md`; `docs/specs/2026-05-18-fieldtest-embedding-abi-m1.md` - [x] **\[todo\]** form_a.md scalar-parameter mode carve-out — docs- honesty tidy (M1 fieldtest friction + spec_gap#1, shared root) — CLOSED 2026-05-18. `crates/ailang-core/specs/form_a.md` stated an *unconditional* "every `(fn …)` param MUST carry an `(own/borrow)` mode" rule in **four** places that contradicts shipped checker behaviour (scalars take **and require** bare `(con Int)`; a mode on a scalar trips body-pointing `use-after-consume` / `consume-while-borrowed`). All four sites rewritten symmetric to the pre-existing return-type carve-out; the already-correct few-shot annotation left verbatim by design; DESIGN.md §"Embedding ABI (M1)" gained the bare-scalar export-param rule + a corpus-grounded `step` Form-A snippet; RED-first anti-regrowth pin via `ailang_core::FORM_A_SPEC` + `norm()` (4 ABSENT + 4 PRESENT form_a + 1 PRESENT DESIGN). Zero language/checker/codegen change; Boss-verified docs_honesty_pin 5/0, spec_drift 8/8 (not a lockstep partner), ailang-core 112/0, workspace 622→623 (+1 = the pin), zero `crates/**/src/**` diff. Pure docs+pin tidy — no audit/fieldtest gate (the pin IS the regression coverage). plan `docs/plans/form-a-scalar-param-mode-carveout.md` (`4c266a6`) → iter `7d7f04e`. Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-fieldtest-embedding-abi-m1.md` findings [friction] + [spec_gap]#1. - [x] **\[feature\]** `ail emit-ir --emit=staticlib` — restore the Decision-5 IR-readability affordance for kernels (M1 fieldtest spec_gap#2) — CLOSED 2026-05-18. `ail emit-ir` had no `--emit=staticlib` (only `ail build` did) and on a `main`-free kernel hit the executable-path `MissingEntryMain` rejection — an author could not read the generated `@` forwarder for an exported kernel. Resolution **added** (DESIGN.md *widened*, never narrowed): a one-line symmetric codegen convenience `lower_workspace_staticlib(ws)` routing through the M1-audited unchanged `Target::StaticLib` path, an `emit` clap field on `Cmd::EmitIr` symmetric with `Cmd::Build`'s, a zero-export guard byte-identical to `build_staticlib`'s; DESIGN.md §"Embedding ABI (M1)" affordance sentence + a CLI-synopsis correction also discharging a pre-existing M1 `ail build --emit=staticlib` omission. No new doc pin (E2E pins behaviour; architect's milestone-close DESIGN.md read catches stale prose). Boss-verified: 3 new E2E 3/0 (incl. functional CLI spot-check — `@backtest_step` external forwarder readable, no `@main`), `embed_staticlib_cli` 2/0 (build-side untouched), `docs_honesty_pin` 5/0, `ail` 186/0, workspace 623→626 (+3), zero out-of-scope diff, no fixture minted. Scoped feature — no audit/fieldtest gate (E2E is the coverage; reuses the M1-audited codegen path, no invariant/surface change). plan `docs/plans/emit-ir-staticlib.md` (`03493c9`) → iter `bcfe554`. Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-fieldtest-embedding-abi-m1.md` finding [spec_gap]#2. - [x] **\[milestone\]** Embedding ABI — M2: per-thread runtime context + concurrency safety — CLOSED 2026-05-18. A compiled scalar AILang kernel is now callable concurrently from a host thread swarm without an RC-runtime data race. `ailang_ctx_t*` is a mandatory leading parameter of the (M3-frozen-shape) C `@(ctx, scalars…)` ABI; the M1 forwarder publishes it via a `__thread` slot around the **byte-unchanged** internal `@ail__` call (internal convention + `_adapter`/`_clos` untouched — M1 decision held; TLS sound because the kernel call is synchronous, ctx never held across a suspension). `runtime/rc.c` de-globalised: the two RC-counter sites became `if (ctx) ctx->{alloc,free}_count++ else g_rc_*++`, the `g_rc_*` statics + `atexit` retained verbatim as the null-ctx single-threaded executable fallback (executable-path leak readback byte-preserved). ctx near-empty by discipline (`{alloc,free}_count` only — no arena/lock/atomic/IO; the build-ahead trap named out-of-scope). Staticlib is RC-only enforced (`--emit=staticlib` rejects `--alloc=gc|bump`; Boehm never linked into a swarm artefact; standing P2 Boehm-retirement untouched). No authoring-surface / schema / `ailang-check` change — the `.ail` is byte-identical to M1; the deliverable is a swarm-safe generated ABI + de-globalised runtime, **sanitiser-verified** (per-thread-ctx scalar swarm tsan-clean == oracle; direct rc-accounting per-ctx clean; shared-ctx negative control a genuine `ThreadSanitizer` race at the de-globalised counters, exit 66 — teeth non-vacuous). Process note: the first implement dispatch correctly BLOCKED on a genuine spec defect (a negative control on the non-allocating scalar swarm is structurally impossible — the spec's own honesty point); Boss adjudicated a spec-consistency repair (teeth relocated to the rc-accounting harness) rather than a brainstorm bounce. spec `1c58055` (grounding-check PASS 9/9) → plan `b3388c8` (Boss-corrected) → iter `c9a84b3` (PARTIAL 4/9 + Boss repair) + `fbeeade` (DONE 5–9); milestone-close `audit` `ad88dec` (architect one `[medium]`+`[low]` doc-honesty drift; bench `check.py` exit 1 decisively causally exonerated — bencher H0-refuted, all 3 firings the two tracked-P2 noise families, rc.c hunk branchless+free, NO ratify) → tidy `a80d495` (the `## Embedding ABI` lockstep rename, drift resolved). No fieldtest (zero authoring-surface change). Stays here briefly for context; remove once stale (full record in `git log`). - context: `docs/specs/2026-05-18-embedding-abi-m2.md`. - [x] **\[milestone\]** Embedding ABI — M3: frozen value layout + single ADT/record crossing + RC ownership contract — CLOSED 2026-05-18. A single-constructor record of `Int`/`Float` fields now crosses the embedding C ABI in **and** out; ownership follows the declared `own`/`borrow` mode (mechanically inherited — the M2 forwarder body is byte-unchanged, all mode-driven RC stays in the byte-unchanged internal `@ail__`); the record memory layout (header@p-8 / i64 tag@0 / fields i64-strided@8+i·8 / size=8+n·8) is **frozen** as a one-way commitment — a new DESIGN.md §"Embedding ABI" `### Frozen value layout` SSOT + `// FROZEN ABI` lockstep pointers at the three encoders + an enforceable `@ailang_rc_alloc` heap-box byte-pin (RED-on-offset- perturbation proven); host construction via `ailang_rc_alloc`, host-free via `ailang_rc_dec` (leak-free *because* M3 fields are scalar — no boxed children; non-scalar recursive-free named M4- additive). No authoring-surface / schema / Form-A / `CheckError` change (M2-style — the `.ail` is the minimal evolution of the M1/M2 scalar kernel into a record `State`). The `(State,Float)-> State` fold round-trip is proven **globally leak-free** for both `own` and `borrow`. Process: spec `1fbb9c4` (grounding-check PASS 8/8) → plan `15ee3c5` → iter `d5c565d` (PARTIAL 5/7 + a Boss spec-consistency repair: the orchestrator correctly BLOCKED on a genuine spec defect — the single-ctx-readback proof model is unsatisfiable for `borrow` by M2's TLS-ctx design; Boss M2.1-precedent adjudication → a stronger global-leak-freedom proof model) + `4ea8bc5` (DONE 6-7: the freeze). Milestone-close `audit` `b8a60b1` (architect: Invariant 1 clean, M1/M2 byte-invariant held, frozen-SSOT consistent — DRIFT only `[medium]`+`[low]` doc-honesty → tidy; bench `check.py` exit 1 **decisively causally exonerated** — byte-identical generated IR HEAD vs pre-M3 `9a609ae` for every firing bench, the two tracked-P2 noise families, NO ratify) → tidy `63d7d60` (pin-safe; drift resolved). No fieldtest (zero authoring-surface change). Stays here briefly for context; remove once stale (full record in `git log`). - depends on: Embedding ABI — M2. - context: `docs/specs/2026-05-18-embedding-abi-m3.md`. - [x] **\[milestone\]** Embedding ABI — M5: `ail-embed` adapter + `data-server` wiring + thread-swarm backtest — **DONE 2026-05-19**, audited + ratified + doc-honest. Terminal milestone of the M1–M5 Embedding ABI arc: a real backtest runs over **real Pepperstone tick data** through the real external `data-server` crate into the shipped M3-frozen AILang kernel, across a thread swarm of independent per-thread embedding contexts. `ail-embed` is a lean reusable embedding module (`extern "C"` to the M3-frozen ABI + frozen-layout box helpers, zero finance knowledge) **plus** the real E2E on top — in-repo but its own cargo workspace root (`[workspace]`-excluded), the sole `data-server`↔AILang meeting point (Invariant 1, architect-confirmed PASS at close). The adapter (not the kernel) owns chunk iteration, unrolling each chunk host-side into per-tick `(State, Tick) -> State` calls (M4's cons-list crossing was retired as speculative infra). Symbol-fan swarm = the headline existence proof (per-thread bit-exact vs an independent host reference); time-shard swarm = the **first actual proof** of the chunk/window-boundary invisibility the M4 retirement rests on (per-shard bit-exact). Globally leak-free, deterministic. Zero language/compiler change; one runtime change (`7bfa11e`: the global RC-stats fallback counters made atomic-relaxed — the swarm exposed that AILang's first concurrent consumer needed it; user-adjudicated bounce-back → RED-first fix, then a build-dependency staleness root-caused + fixed). Audit: Invariant 1 PASS, M3 frozen-layout SSOT unmoved, bench `gc_rss` trio evidenced-RATIFY (a Boehm conservative-scan artefact of the necessary atomic fix; Decision-9 Boehm-transitional), P2 noise causally exonerated baseline-pristine; doc-honesty tidy clean. **Friction-harvest deliverable: host-per-tick-FFI ≈ ~206 ns/tick at real EURUSD volume** — the P2 flat-array decision input. Stays one cycle for context, then prune. - depends on: Embedding ABI — M3 (shipped); Tick-coverage on M3 (shipped `170464f`). - context: `docs/specs/2026-05-19-embedding-abi-m5.md`. - [x] **\[milestone\]** Heap-`Str` ABI — runtime infrastructure for malloc-backed, refcounted `Str` values alongside the existing static `@.str_*` globals. Today the `Str` path is static-only (DESIGN.md §"Float semantics" notes this explicitly), so any primitive that needs to produce a `Str` at runtime — `int_to_str`, `float_to_str` (currently type-installed but `CodegenError::Internal` on call), eventual `Show.show`, future `++` on strings — cannot ship. Scope: pick the representation (likely a `{rc_header, len, bytes…}` slab consistent with the rest of the RC runtime), teach codegen to accept both static and heap `Str` at the same ABI slot, wire RC `inc`/`drop`/`clone`/`compare`/`eq` on the heap form, and ship `int_to_str` + `float_to_str` as the first two callers so the ABI gets exercised end-to-end. Unblocks Show + print rewire below. - context: DESIGN.md §"Float semantics" (`float_to_str` is type- installed, codegen-deferred); spec 2026-05-11-23-eq-ord-prelude §"Show. Defers behind a heap-Str-ABI milestone"; spec 2026-05-10-fieldtest-floats §F4 ("dynamic Str allocation in the runtime"); spec 2026-05-09-22-typeclasses §22b.4b ("Show#Int needs an `int_to_str` primitive returning heap-allocated Str"). - [x] **\[milestone\]** Post-22 Prelude — Show + print rewire — shipped 2026-05-13 as iters 24.1 (heap-Str runtime + codegen for `bool_to_str` + `str_clone`, f38bad8), 24.2 (prelude `class Show` + four primitive instances Int/Bool/Str/Float + 22b TShow/tshow migration), and 24.3 (polymorphic `fn print : forall a. Show a => (a borrow) -> () !IO` + positive 4-prim E2E + user-ADT E2E + Show-aware NoInstance diagnostic + DESIGN.md amendments to §"Prelude (built-in) classes" and §"Float semantics"). The `MethodNameCollision` workaround that blocked the original spec retired in mq.3 (2026-05-13); spec `docs/specs/2026-05-13-24-show-print.md` re-derived 24.2 + 24.3 against the post-mq architecture. - context: spec `docs/specs/2026-05-13-24-show-print.md`. ## P2 — Medium-term - [x] **\[milestone\]** DESIGN.md → `design/` — CLOSED 2026-05-19. The 3020-line `docs/DESIGN.md` is **deleted** (clean cut, no stub) and replaced by the `design/` ledger: `design/INDEX.md` (sole addressable spine, typed Contracts+Models tables with polymorphic links — prose file OR authoritative source `//!`), 14 `design/contracts/*.md` test-linked invariants + 3 source-link-only contracts (mangling/env-construction/ qualified-xref — code is SoT), and 5 `design/models/*.md` whitepapers. RED-first `design_index_pin.rs` 4-clause anti-regrowth spine; clause-3 is a hand-rolled **faithful Sweep-1 superset** so the in-code hard gate enforces the honesty spirit (clause-3 GREEN ⟹ Sweep-1 clean in contracts/). Build-atomic by task ordering (the only compile-time consumer's `include_str!` retargeted before the deletion). Every live `DESIGN.md` reference — 4 executables, 2 diagnostics + 2 E2Es, ~12 agent reading lists, 5 SKILL bodies, CLAUDE.md, README, ~25 code/C/.ail/spec comment xrefs — retargeted in lockstep; the honesty rule rewritten to name the new rationale home. Process: spec `a64b2cc`/`314e5e4` (grounding-check PASS ×2) → plan `deeffb1` → iter .1 `176821c` (DONE 9/9) → `audit` `2ba5e16` (architect drift_found `[medium]`+`[low]`, relocation byte-faithful; bencher causally-exonerated DECISIVE on byte-identical IR+binaries, baseline pristine — M2/M3/M5 disposition) → tidy `f2cdd67`/ `f683f1a` (DONE 7/7; the audit Resolution mechanism+scope corrected on planning-time evidence after a correctly-BLOCKED plan defect — the "two+ defects ⇒ fix the upstream artifact" discipline, not a third patch). No fieldtest (zero authoring-surface change — reasoned exclusion). Stays briefly for context; remove once stale (full record in `git log`). Original decided-shape rationale retained below for context until pruned. **Motivation.** The just-closed `docs-honesty-lint` milestone is the proof this is not a cleanup problem: it ran a full docs pass and DESIGN.md stayed 2905 lines, because honesty-lint operates *within* a job (tense / Wunschdenken / citation) and its own audit-trail invariant *mandates retaining* the bulky decision-record prose (DESIGN.md:242 "records the *why* … for the audit trail"; the architect Sweep-5 discriminator explicitly keeps "present-tense design rationale"). You cannot clean your way out of conflation — the conflation itself is the structural defect. The three conflated jobs and their distinct consumers: - **Contract layer** — prescriptive, test-linked invariants (e.g. Decision 6's seven hard constraints, the Roundtrip Invariant, the borrow/own binding rules). Consumer: `architect` (mandatory full read at *every* milestone close), `grounding-check` (every spec), the bench drift lints. Wants: structured, addressable, test-linked, small, hot. This is the only job that belongs on the per-milestone hot path. - **Model exposition** — whitepaper-shaped model narratives (RC + Uniqueness, typeclasses, effects). Consumer: onboarding (fresh-context LLM, `fieldtester`). Irreducible — the code cannot speak the gestalt; one whitepaper per model. - **Decision-record / relitigating-guard** — why X was chosen, why Y/Z were rejected (region inference, tracing GC, …). Consumer: a future `brainstorm`, so it does not re-propose a settled-and-rejected idea. (This tier was migrated out of DESIGN.md at split time and later retired entirely; the project's history lives in `git log`.) Underlying principle: the code is authoritative for *what it does* — delete every description of behaviour, the code speaks; the spec's irreducible job is *what is promised* plus a pointer to the green test that ratifies it (code answers *what*; spec answers *what is promised*; test answers *does the promise still hold*). **Decided shape.** `design/` split on the consumer/lifetime axis — **not** by Decision-number (that is cosmetic; the architect would still read everything). `design/contracts/` (the hot, test-linked invariant set), `design/models/` (one whitepaper per model). `design/INDEX.md` is the typed ledger spine: per entry a one-liner + metadata `{kind, ratifying-test, consumer/lifetime}` + a content link whose target is polymorphic — a `design/contracts/…` file, a single-owner `//!` source header (mangling, env, roundtrip, float, tail-calls, data-model), or a `design/models/…` whitepaper. INDEX.md is the sole addressable entry point. Decision-records move out of DESIGN.md; the honesty-lint audit-trail invariant is repointed in the same milestone. **Rejected — do not relitigate.** Quarto / `.qmd` was evaluated and rejected: every distinctive Quarto feature (rendered HTML/site, figures, citations, cross-ref resolution, executable chunks) is render-time value for a *human reader who does not exist here* — the `design/` consumer is an LLM reading raw files. Executable chunks would reintroduce a second "is the invariant green?" truth that can diverge from `cargo test` (the duplicate-source-of-truth failure mode); Quarto `@ref` cross-refs degrade the raw-file reader (unresolved tokens vs. resolving relative-path links); plus a non-Rust toolchain dependency for zero in-loop value. Plain Markdown + a typed INDEX.md is strictly better for this consumer. A plain shard by Decision-number is likewise rejected (changes nothing for the architect hot path). **Sequencing / blast radius.** Deliberately scheduled *after* the in-flight Embedding ABI arc — a substantive sequencing reason, not effort. `DESIGN.md` is referenced by name by at least `bench/check.py` (history-anchor / `design_schema_drift`), `bench/architect_sweeps.sh` (Sweep 5; exit 2 = "could not find DESIGN.md"), the reading lists of `ailang-architect` / `ailang-grounding-check` / `ailang-fieldtester`, the CLAUDE.md "Roles of docs/…" section, and the honesty-lint invariant's own scope — load-bearing invariants and agent contracts, not just paths. Every Embedding-ABI milestone close runs `audit` (architect + bench) against DESIGN.md; restructuring it mid-arc would break the architect's reading list and the drift scripts *under* an in-flight milestone. Hence no overlap with active implementation that closes audits against the current DESIGN.md. Brainstorm hard-gate before any plan/code — it rewrites enforced invariants and agent contracts. - context: spec `docs/specs/2026-05-19-design-md-rolesplit.md` (incl. the Boss-adjudicated relocation Appendix; grounding-check PASS ×2); origin 2026-05-18 chat (DESIGN.md-management dialogue — six-turn convergence). CLOSED — audited + drift-resolved; hard gate enforces the honesty spirit. - [x] **\[milestone\]** Formal cross-links in the `design/` ledger (browsable wiki) — CLOSED 2026-05-19. The positive completion of DESIGN.md → `design/`: informal prose cross-references between contracts/models are now **formal file-relative Markdown links** resolved relative to the containing file, gated by RED-first `design_index_pin.rs` **clause-5** that fails the build on any body link that does not resolve into the durable tier (`design/` + `crates/**` + `runtime/**` only — never `docs/`, never a `#fragment`). clause-5 ∘ clause-3 = complete invariant: every contract cross-reference is a resolving durable file-link or clause-3-forbidden history prose. INDEX spine stays repo-root-relative (registry tier, clause-1 byte-unchanged) — the move-fragility rationale that drives body prose to file-relative is absent for the file that never moves. Shipped in one iter (5/5 tasks): clause-5 with `strip_fences` (toggle on ```/~~~ so a `](` inside a fence is not treated as a link) + RED-first via identity-stubbed `strip_fences` synthetic vectors; 7 prose conversions (8 link tokens — float-semantics:69/100, embedding-abi:45, memory-model:44/105, scope-boundaries:48/88 with mixed-referent split into a source link + a Pipeline cross-file link); clause-6 disposition (b) on the 2 PROSE_ROUNDTRIP homeless pointers (pointer removed, behavioural `ail merge-prose` prose preserved); pin-safe positive-half paragraph in `honesty-rule.md`. - context: spec `docs/specs/2026-05-19-design-ledger-formal-links.md` (grounding-check PASS ×3 across two corpus-grounded amendments — clause-6 + cross-ref definition; clause-5 fence-skip + closed convert-set enumeration); plan `docs/plans/design-ledger-formal-links.1.md`; origin this session's six-turn design conversation following the split close. CLOSED — audit clean (zero drift, bench trio 0/0/0); no tidy, no fieldtest (zero authoring-surface change — reasoned exclusion). - [ ] **\[milestone\]** Flat array/slice primitive — performance follow-up to the Embedding ABI arc, *not* a capability gap. AILang's only sequence is the recursive `List` ADT (one RC cell per element). The ABI arc resolved chunk-crossing by having the M5 adapter unroll each `data-server` chunk host-side into per-tick `(State, Tick) -> State` calls (M4's cons-list crossing was retired as speculative infra) — so the residual perf question is no longer "1024-cell cons-chain per chunk" but **host-per-tick-FFI vs. an eventual batch/flat-array crossing**. M5's friction-harvest measured the per-tick FFI at **≈ ~206 ns/tick at real EURUSD volume** (≈ 658 ms / 3.19 M ticks). Open decision: whether a contiguous array/slice primitive (to amortise that per-tick cost via a batch crossing) is worth a *language* change — it interacts with uniqueness inference, RC, and the structurally-decreasing-recursion totality story, and is out of the (now-closed) ABI arc's scope. Now decidable on the measured number, not speculation. - depends on: Embedding ABI — M5 (shipped; measured ~206 ns/tick — the justification input now exists). - context: 2026-05-18 chat (user deferred this to keep the ABI arc clean); the friction-harvest number recorded in the M5 audit commit; M4 retirement decision recorded in the M5 closing commits. - [ ] **\[milestone\]** Iteration-totality story — structural + Int-bounded total recursion with *enforced* non-negativity. AILang's iteration story stays as-is (structural / tail recursion; `tail-app` intact). The genuine ambition — make `f(n-1)`-family recursion (incl. branching tree builders) total *by construction* with the non-negative-entry precondition **enforced**, not merely documented — is deferred here because doing it without a purity- pillar concession requires refinement/`Nat` type machinery the language has not built (Decision 4 keeps refinements opaque, no SMT). Not abandoned; correctly sequenced after the type machinery. - depends on: a future `Nat`/refinement-types milestone (no spec yet). - context: `docs/specs/2026-05-16-iteration-discipline-revert.md` (why the 2026-05 attempt was reverted); the branching-builder counter-example that surfaced the gap landed in the it.3 iter commit. - [x] **\[milestone\]** Retire `io/print_int` / `io/print_bool` / `io/print_float` effect-ops + migrate example corpus to `print`. Shipped 2026-05-14 as iter rpe.1. - context: shipped in the rpe.1 iter commit. - [x] **\[todo\]** Author `examples/prelude.ail` alongside `examples/prelude.ail.json`. (Satisfied 2026-05-13 by iter form-a.0 — `examples/prelude.ail` rendered via `ail render`, 116 lines / 6386 bytes, round-trip-CI green.) - [x] **\[milestone\]** Form-A as the default authoring surface for examples and docs. (Closed 2026-05-13 by iter form-a.1.) Render every `examples/*.ail.json` to its `.ail` sibling via `ail render`, **delete the now-redundant `.ail.json`**, and regenerate the JSON-AST per `ail parse` at build / test time. Same for inline JSON-AST blocks in `docs/` markdown (~7 in DESIGN.md plus ~29 other md files) — convert to Form-A snippets where the snippet's purpose is to show "what the language looks like", not "what the schema is". After this milestone the working tree contains exactly one representation per program: the `.ail` source. The JSON-AST is a build artefact, not a checked-in twin. Tests and benches that currently glob `*.ail.json` either parse-then-consume or are rewired to point at `.ail` directly. The round-trip invariant flips role: today it gates that the two forms agree; afterwards it gates that `parse` is deterministic. Carve-outs that MUST stay JSON-AST (no Form-A counterpart, and no `.ail` sibling shall be created — these are the only seven files that remain `.ail.json`-only post-milestone): - Fixtures that test canonical-form rejection — Form A would reject them at parse, defeating the test: `test_ct1_bare_xmod_rejected.ail.json`, `test_ct1_qualified_class_rejected.ail.json`, `test_ct1_bad_qualifier.ail.json`, `broken_unbound.ail.json`, `test_22b2_invalid_superclass_param.ail.json`, `test_22b2_kind_mismatch.ail.json`, `test_22b2_unbound_constraint_var.ail.json`. - DESIGN.md schema documentation blocks where the JSON-AST shape *is* the point (Decision 11, ParamMode, canonical-form invariants). - Any other case where the structured form is the artefact under discussion, not a vehicle for a program. Touches CLAUDE.md ("source of truth is structured data") — the language doctrine doesn't change (JSON-AST is still the canonical hashable form), but the *authoring* doctrine does: authors write `.ail`, the build derives JSON-AST. Sentence in CLAUDE.md needs rewording in the same milestone. Mechanical for the bulk; per-fixture judgement call only for the carve-out list. Run as one milestone so the corpus flip-over happens at a single, audit-gated point. - context: post-Form-A-as-canonical-authoring corollary of the `examples/prelude.ail` entry above. Generalises the same idea to the rest of the corpus and follows through on the cross- model authoring data (textual form cheaper, more first-try hits) by treating Form A as the privileged surface in the working tree, not just in flavour text. - [ ] **\[feature\]** Operator routing through `Eq` / `Ord` — `==`, `<` etc. resolved via the typeclass instead of the built-in primitive comparators. No commitment; gated on bench re-baselining to make sure the indirection doesn't tank latency. - context: `git log --before=2026-05-11 --grep=...` for the pre-archive-cutoff rationale. - depends on: Post-22 Prelude — Eq/Ord (shipped 23.5) - [x] **\[todo\]** `types` / `ctor_index` overlay shape question — decide whether the env's two parallel ctor maps should collapse into one overlay, or stay split. Surfaced during the env-construction unify audit. - context: closed by iter ctt.1 — DESIGN.md §"Env construction" anchors the split decision. - [x] **\[todo\]** CLI human-mode diagnostic surface for `WorkspaceLoadError`. Shipped 2026-05-14 as iter cli-diag-human — a new `load_workspace_human` helper in `crates/ail/src/main.rs` routes 9 non-JSON `ailang_surface::load_workspace(&path)?` call sites through `workspace_error_to_diagnostic`, so the bracketed `[code]` prefix is preserved across `ail check`, `build`, `run`, `emit-ir`, `prose`, `describe`, `deps`, `diff`, `manifest`. - context: shipped in the cli-diag-human iter commit. - [x] **\[todo\]** Retire dead `KindMismatch` arm — `validate_classdefs`'s `walk_kind_mismatch` path is structurally unreachable through well-formed schema post-ct.1 (the canonical-form validator catches the malformed `Type::Con { name: param }` shape earlier). The enum variant + `walk_kind_mismatch` helper stay as dead-but-defensive code; a future tidy can delete both. - context: closed by iter ctt.3 — variant + helper + dispatch + Display arm all deleted; canonical-form-rejection test stays green asserting `BareCrossModuleTypeRef`. - [x] **\[todo\]** Re-key `Registry.type_def_module` to handle bare-name-collision-across-modules — `BTreeMap` keyed by bare type name silently overwrites when two modules each define `type Foo`; `normalize_type_for_registry` would then collapse `M.Foo` and `N.Foo` to whichever insert won. Acceptable for current corpus (distinct bare type names across modules), but the proper fix is to key by `(owning_module, bare_name) → defining_module`. - context: flagged by the ct.1.5a quality reviewer. - [ ] **\[feature\]** 22c — typeclass corpus expansion. User-defined classes beyond the prelude four; multi-parameter classes; superclass chains; richer instance bodies. Deferred from milestone 22. - context: `git log --before=2026-05-11 --grep=...` for the pre-archive-cutoff rationale. - [x] **\[milestone\]** Module-qualified class names + type-driven method dispatch — retired the `MethodNameCollision` workaround; shipped 2026-05-13 as iters mq.1 (canonical-form extension for class-ref fields + workspace-internal qualification), mq.2 (type- driven dispatch mechanism installed: `method_to_candidate_classes` inverse index, multi-candidate `ResidualConstraint`, `resolve_method_dispatch` 5-step rule, `AmbiguousMethodResolution` + `UnknownClass` diagnostics), and mq.3 (retirement + multi-class E2E + `class-method-shadowed-by-fn` warning + DESIGN.md sync). Two libraries can now each declare `class Eq` with their own `eq`; cross-class method ambiguity is resolved at the call site via type-driven dispatch with `..` as the disambiguation form. - context: `docs/specs/2026-05-10-canonical-type-names.md` "Out of scope: Class names" — the workaround was named there so it stayed visible until this milestone retired it. - [ ] **\[todo\]** Boehm full retirement — remove the transitional Boehm GC path now that RC + uniqueness is the canonical memory story. - context: pre-milestone-22 "Boehm transitional" decision — see commits from that window. - [ ] **\[feature\]** Closure-pair slab / pool — codegen tweak to pool the env+code closure pairs instead of one-shot heap allocs. Bench-gated. - [ ] **\[todo\]** `FnDef::synthetic` flag — formalise the monomorphiser-emitted FnDefs so downstream passes can tell user-authored from synthesised at a glance. Currently inferred from symbol naming. - [ ] **\[todo\]** 21'h iteration — final 21' carry-over (latency methodology pass). Numbering kept for continuity with the 21' arc. - [x] **\[todo\]** DESIGN.md effect-prose is fiction — standalone documentation-honesty tidy. Shipped 2026-05-16 as iter effect-doc-honesty (a29700c): the three false effect-system claims (row-polymorphic `![IO | r]`; `IO`+`Diverge` both wired up; `Term::Do` "effect-handler table at link time") reconciled to the real flat-closed-set / IO-only / `IndexMap`+codegen-`match` mechanism, satellite lockstep done, guarded by a 4-test doc-presence pin. No language/checker/codegen change. - context: shipped in the effect-doc-honesty iter commit. - [ ] **\[todo\]** `io/print_float` always-emit-`.0` — surface printer always emits `.` or `e/E` so re-lex routes to Float; the runtime printer (`printf("%g\n", v)`) doesn't, so `2.0` prints as `2` (Int-shaped). Asymmetric. Either switch the runtime path to a `.0`-fallback printer (matching surface) or document the `%g` contract in DESIGN.md §"Float semantics" so the LLM-author knows `io/print_float`'s output is for-humans not round-trip. - context: `docs/specs/2026-05-10-fieldtest-floats.md` finding F1. - [ ] **\[todo\]** Rustdoc warning sweep — `cargo doc --no-deps` reports 16 pre-existing warnings (15 in `ailang-check`, 1 in `ailang-core`: private-item links from public doc, unresolved intra-crate links). All predate the design-md-consolidation milestone; treat as a one-off sweep. - context: surfaced in the design-md-consolidation audit close (2026-05-10). - [ ] **\[todo\]** `ailang-plan-recon` site-undercount countermeasure (P2, **escalated** — now a structural recon-contract defect, no longer a single-milestone curiosity) — the recon agent hand-lists the change blast radius and has under-counted it **four times across two milestones, through a different site type each time**: loop-recur.1 walker arms, loop-recur.2 cross-module `synth` callers, loop-recur.tidy implicit, and now remove-mut-var-assign.1 (in-source `mod tests` fns + a drift-pin fn + 5 orphaned `.ail.json` carve-outs + a non-enumerated `codegen_import_map_fallback_pin.rs` E0599) **plus a spec-named doc the recon was told did not exist** (`crates/ailang-core/specs/form_a.md` — the spec listed it for deletion; a Boss plan-time grep checked only `docs/form_a.md`, concluded "no such file", and propagated that into the recon brief; caught only at milestone-close audit). Two distinct gaps: (a) the compile-driven sweep catches exhaustive-`match`/caller misses but **not** non-compile-checked sites (docs, fixtures, drift pins) — those need a separate "every spec-named path is verified to exist and is handled" cross-check; (b) a recon brief must never inherit an unverified "X does not exist" — existence claims feeding a recon are themselves load-bearing and must be tree-wide, not dir-scoped. Tighten `skills/planner/agents/ailang-plan-recon.md`: for any signature-change / enum-variant / removal scope the recon REPORTS the compile-driven enumeration as the authoritative code-site set (hand-list advisory) AND emits a spec-named-path existence table (every path the spec names, `ls`-verified, with its handling task). No language change; an agent-definition discipline fix. - context: loop/recur close audit (architect `[low]`, 2026-05-18) + remove-mut-var-assign close audit (architect `[high]` form_a.md + `[medium]` process-drift, 2026-05-18); pairs with planner Step-5 items 7+8 (those scrub the *plan*; this scrubs the *recon* and the *recon brief*). - [ ] **\[todo\]** `design_schema_drift.rs` fidelity widening — current test checks anchor *presence* anywhere in DESIGN.md; the audit found that `[high]` schema gaps in §"Data model" are invisible because anchors live in Decision 11 instead. Constrain the test to scan only §"Data model" + ParamMode block, or extract JSON-schema blocks into a machine-readable file the test consumes. - context: surfaced in the 2026-05-10 audit close. - [ ] **\[todo\]** Split `BadCrossModuleTypeRef` into two diagnostics — the current single shape collapses unknown-owner and known-owner / unknown-type-in-owner into one message. The two cases suggest different fixes (add `(import )` vs. fix the type name). In the known-owner branch, list the owner's available type defs as candidates the way `bare-cross-module-type-ref` lists candidates from imports. - context: fieldtest 2026-05-11 — `examples/ct_3*.ail` exhibits both branches with identical-shape diagnostics. - [ ] **\[todo\]** Zero-arg `(app f)` rejected at parse — the Form-A parser refuses an application with an empty argument list, so a nullary call has no surface form. Surfaced by the mut-local fieldtest (F3) AND **independently re-confirmed by the loop/recur fieldtest** (2026-05-18, finding spec_gap): the maximally-natural infinite-event-loop shape is a niladic `run_forever : fn() -> Int` called `(app run_forever)`, which dies at parse before reaching loop/recur semantics. Two independent fieldtests hitting the same gap raises the priority signal. Decide: accept `(app f)` as the nullary-call surface, or ratify in DESIGN.md that nullary functions are expressed differently (and say how). DESIGN.md's `Term::App` `args:[Term...]` states no minimum, so the surface "expected at least one argument" rule is unbacked by spec — a genuine design fork, deliberately NOT auto-ratified under autonomous orchestration. Not a blocker; no current corpus program needs it, but an LLM author reaches for it. - context: `docs/specs/2026-05-15-fieldtest-mut-local.md` finding F3; `docs/specs/2026-05-18-fieldtest-loop-recur.md` spec_gap. - [ ] **\[todo\]** Module-level `(doc …)` diagnostic omits where `doc` belongs — a `(module NAME (doc "…") (fn …))` is correctly rejected (`unknown def head \`doc\``) but the message lists valid def heads without saying doc strings attach *inside* `fn`/`data` defs; an author can read it and conclude doc strings are unsupported. One-line tidy: append a hint like "(doc strings attach inside `fn`/`data` defs, not at module level)". Low cost; verbose-diagnostic-philosophy gap, not a bug. - context: `docs/specs/2026-05-18-fieldtest-loop-recur.md` friction. - [ ] **\[todo\]** Workspace search beyond entry-module's directory — `load_workspace` only finds sibling `.ail.json` files in the same directory as the entry module, so any consumer of prelude/std in a subdirectory has no way to resolve cross-module imports. Add either a `--workspace-root` flag on `ail check` / `ail build` / `ail run`, or upward-search from the entry module's directory. Alternatively ratify the flat-workspace assumption in DESIGN.md if intentional. - context: fieldtest 2026-05-11 — fieldtest fixtures could not be placed under `examples/fieldtest/` because of this; predates the canonical-type-names milestone but surfaces every time. - [ ] **\[todo\]** `*.bump_s` throughput baseline is stale vs current hardware — `bench/check.py`'s `throughput.*.bump_s` family (the fastest, most jitter-prone metrics) reads ~+5–13% over `bench/baseline.json` on the current machine. Localised at the iteration-discipline-revert audit (2026-05-16): an interleaved 3×60-run measurement of `bench_list_sum` bump_s built from the byte-oracle commit `1ff7e81` shows the *same* ~+11% elevation as HEAD, and the two bump binaries are `cmp`-identical — so this is environmental drift relative to the 2026-05-09 baseline-capture machine state, **not** a codegen regression. Re-capture the full `*.bump_s` set on current hardware from a known-clean commit and recalibrate the `bump_s` baseline+tolerance pair (or widen the tolerance) so the noise floor stops tripping `check.py` exit 1. Pure bench-harness recalibration; no language change. - [ ] **\[todo\]** `check.py` RC-latency `*.max_us` is a structural false-positive at `-n 5` — **distinct** from the `*.bump_s` staleness above (different metric family, different root cause). `latency.{explicit,implicit}_at_rc.max_us` is the single worst of ~5000 samples over only 5 runs, dominated by OS scheduling / THP / IRQ jitter on a shared host, not allocator behaviour. It has fired a false `REGRESSION` on **three consecutive no-runtime-change milestones** (iteration-discipline-revert, prose-loop-binders, remove-mut-var-assign) and vanished on identical-code re-run every time (remove-mut-var-assign close: HEAD vs `48e7774` bench binaries `cmp`-byte-identical, `explicit_at_rc.max_us` collapsed +108%→-2.30% ok by rerun3) — a ~3-for-3 false-positive rate on null changes, while the median/p99/p99.9 of the same benchmarks held across all re-runs. Pick one mitigation: drop `*.max_us` from the gating set (keep median/p99/p99.9, which are the trustworthy signal), or raise `-n` substantially for the tail metrics, or pin the latency arm to an isolated cpuset. Pure bench-harness change; no language change. - context: remove-mut-var-assign close audit, bencher localisation (2026-05-18) — byte-identical-binary causal exoneration + the 3-milestone false-positive history. - context: the bencher localisation evidence in the iteration-discipline-revert audit commit. - [x] **\[todo\]** `check_in_workspace` per-module overlay narrowing — `crates/ailang-check/src/lib.rs:1234` still clears+rebuilds `env.ctor_index` per-module; ct.3.2 narrowed the analogous mono overlay to types-only. The typecheck-side overlay's `env.ctor_index` half serves the duplicate-detection diagnostic at workspace-build time, not the runtime ctor lookup (which is type-driven post-ct.2.2). Narrowing is mechanical but needs a careful read to confirm no other consumer survives. - context: milestone close follow-up; closed by iter ctt.1 — recon confirmed the rebuild is the load-bearing consumer of in-band DuplicateCtor (pinned by `crates/ailang-check/tests/duplicate_ctor_pin.rs`); the asymmetry with the mono side is intentional. - [x] **\[feature\]** `str_concat : (borrow Str, borrow Str) -> Str` — heap-Str concatenation primitive. Shipped 2026-05-13 as iter str-concat (closes fieldtest-form-a friction #4). Symmetric to the iter 24.1 `str_clone` / `int_to_str` / `bool_to_str` plumbing: runtime C helper (`ailang_str_concat`), `ailang-check` builtin registration, `ailang-codegen` extern + `lower_app` arm, plus a fresh `examples/show_user_adt_with_label.ail` corpus fixture exercising the LLM-natural Show-body shape. - context: shipped in the str-concat iter commit. - [~] **\[milestone\]** Stateful islands — bounded mutation for streaming workloads (`Stateful a b` + `!Mut` effect + `mut` syntactic block). Adds a sealed mutable-state layer on top of the pure core: a `Stateful a b` first-class type whose interior is mutable, whose exterior is a typed callable with `!Mut` in its effect set, and whose state non-aliasing is enforced by uniqueness inference at the block boundary. Targets the online / streaming workload class — rolling indicators, IIR filters, online aggregates, sensor fusion, online learning — whose mathematics is "new sample + old state → new state + output" per step, and which today's pure-functional state- threading makes ergonomically expensive at scale (multi-record explicit threading for the canonical sliding-window SMA, no zero-allocation pipe combinator, growing tuple-state types as pipelines lengthen). **Sub-milestone sequencing is UNDER RE-THINK with the user (2026-05-16) — no further sub-milestone is planned or brainstormed until that conversation happens.** Why: the 2026-05-15 decomposition named "(2) effect-handler infrastructure as a prerequisite for any non-IO/non-Diverge effect" as the next step. A read-only recon of the live effect subsystem (2026-05-16) showed that premise is false: the effect raise / declared-set / `UndeclaredEffect`-subset / call- propagation machinery is already fully generic over an arbitrary effect string; `!Mut` needs **no** effect-handler machinery. The only real code prerequisite the recon found is one hard-coded assumption (`linearity.rs` walks every `Term::Do` arg as `Borrow`; `EffectOpSig` has no per-arg mode field) — a single struct field, not a milestone. A brainstorm spec that tried to make sub-ms-2 a standalone deliverable bundled that speculative one-field capability with an unrelated DESIGN.md honesty fix; the user correctly rejected the bundle as incoherent and the build-ahead-of-consumer half as the iteration-discipline trap repeated. **Resolution:** (a) the DESIGN.md effect-honesty correction is split out and runs now as a standalone documentation tidy (see the P2 `[todo]` "DESIGN.md effect-prose is fiction" below); (b) the `arg_modes` finding is recorded as recon context for the future `!Mut` design, NOT built ahead — it is first-iteration material of whatever the `!Mut` milestone turns out to be, validated there against a real consuming op, never a synthetic test op; (c) the old "(2)…(5)" sequence (effect-handler infra → `!Mut`+`ref a` → `MutArray a` → `Stateful a b`+`pipe`) is no longer treated as settled — the whole ordering and granularity is what the pending user conversation re-decides. **Motivation.** AILang's signature-as-contract thesis is *better* served by an explicit `Stateful a b` + `!Mut` annotation than by the implicit-closure-mutation idiom of myc / Lua / JS factory patterns: the signature tells the truth about time-identity without the body needing to be read — exactly the LLM-author correctness affordance AILang exists to deliver, extended to a workload class it does not yet serve. Decision 10's constraint #3 forbids *shared* mutable refs (DESIGN.md:1082); it does not forbid uniqueness-bounded mutation. Lean 4 (`ST`), Roc (`Task`), Haskell (`ST`/`IO`), and Koka (effects) all use a layered design of this shape to host exactly this workload. AILang's existing `own` / `borrow` mode machinery plus its effect-slot architecture are the foundation; this milestone supplies the layer that sits on top. **Scope (subject to brainstorm refinement).** - `Stateful a b` as a first-class type — a sealed callable with a hidden mutable env, externally a typed callable whose effect set includes `!Mut`. - `!Mut` effect, the first non-IO / non-Diverge effect; forces the effect-handler infrastructure forward. - `mut` block as the syntactic boundary in Form A — outside, AILang's pure self; inside, `var` / `assign` / mutable arrays legal. (Iteration is *not* part of this boundary: AILang has no `while`/`for` and this milestone does not introduce one — repetition stays recursion, exactly as the language has it today (structural / tail recursion); a `mut` block is a sealed expression, never a loop over mutable state.) - `var x = expr` + `assign x expr` AST nodes, legal only inside `mut`. - Mutable array primitive (`MutArray a`, O(1) index/update under uniqueness) — co-developed because the ring-buffer use case that motivates the whole effort has no carrier today. - `pipe : Stateful a b → Stateful b c → Stateful a c` as a built-in combinator with zero-allocation lowering — composition is fusion at codegen, not closure-pair layering at runtime. - Decision 12 (or amendment to Decision 10) that names uniqueness-bounded mutation as the legitimate exception to "no shared mutable refs", and the pure / mutable-island layering as the architectural shape. **Blockers (hard prerequisites + open design questions).** - *Effect handlers absent.* DESIGN.md:2663 — "No effect handlers — only the built-in IO and Diverge ops." `!Mut` is the first non-trivial effect and forces handler infrastructure to ship. May warrant lifting out as its own prerequisite milestone; brainstorm decides. - *Uniqueness inference through `var` captures.* Current inference operates over the immutable RC graph; mutable bindings captured by closures need a more powerful pass. Lean 4 has a known algorithm; AILang does not implement it. - *No mutable-array primitive.* No `Array a`, no slab container of any kind in the language today. Separate spec needed inside this milestone (representation, `own`-only or `borrow`-able, bounds-checking discipline). - *`runST`-equivalent escape discharge.* Producing a `Stateful` that legitimately escapes its `mut` block while proving the inner state doesn't leak. Haskell's rank-2 trick (`runST :: (forall s. ST s a) -> a`) is unavailable — DESIGN.md:1930 confirms higher-rank polymorphism is not supported. Need an alternative — likely sealed-by-construction at the factory boundary, or an effect-mode tag that gates escape. - *Form A surface design.* Decision 1 forbids macros (source = data, not text), so `mut` / `var` / `assign` are genuine AST nodes with round-trip-invariant coverage. Surface needs LLM- utility validation (does the author reach for `var` / `mut` unprompted?) before implementation. - *Codegen for in-place struct-field writes.* `Term::ReuseAs` today lowers ADT in-place rewrite; no direct mutable struct- field-write path exists. `crates/ailang-codegen/src/escape.rs` plus the lowering passes need extension. - *Boundary escape analysis.* "Interior state doesn't leak" is an escape analysis specifically over `var` / `ref` values; the existing pass covers allocations, not mutable cells. - *Decision-10 status.* Whether to amend Decision 10 inline or add a Decision 12 that names the mutable-island layer alongside the pure layer. The latter is probably cleaner — Decision 10 stays load-bearing for the pure layer, Decision 12 names the extension and its discipline. - *Streaming bench corpus.* Current corpus (list_sum, tree_walk, closure_chain, hof_pipeline) is all pure. Streaming-specific benches (SMA pipeline, IIR filter, online stats) plus an external baseline (myc, hand-C, Python/NumPy) need to exist to validate that the layered design hits the zero-alloc performance target that myc demonstrates. - *LLM-utility test.* DESIGN.md §"Feature-acceptance criterion" is the gate: the surface must produce code an LLM author naturally writes. Fieldtest after spec, before any code commits. - context: 2026-05-15 chat on the `~/sma_factory.myc` analysis — myc's stateful-closure-plus-pipe idiom delivers a streaming workload pattern (3-line SMA factory, 2-line pipeline, zero runtime allocation per tick) that AILang's pure-only model cannot match without this layered extension. Pending brainstorm will produce `docs/specs/-stateful-islands.md` and decide the effect-handler-prerequisite question. ## P3 — Ideas - [x] **\[todo\]** `compare_primitives_smoke.ail` counterpart. Satisfied 2026-05-13 by milestone form-a-default-authoring — `examples/compare_primitives_smoke.ail` is the canonical authoring form for that fixture. Form A is now the default authoring surface across the entire corpus. - context: closed incidentally by form-a iter form-a.1. - [ ] **\[todo\]** Codegen `lookup_ctor_in_pattern` type-anchoring — `crates/ailang-codegen/src/lib.rs:1790` still walks every module's ctor_index by bare ctor name. Plumbing the scrutinee's qualified `Type::Con` through pattern lowering would type-anchor it symmetric to the ct.2.2 typecheck-side fix. Not load-bearing (uniqueness is enforced at typecheck), but cleaner. - context: surfaced in iter ct.3 + ct.4 close (2026-05-11). - [ ] **\[todo\]** `compare_primitives_smoke` IR-shape assertion — observe `compare__Int` / `compare__Bool` / `compare__Str` symbols in the emitted IR. Blocked on `emit-ir` CLI not running mono; resolution paths include extending the CLI to run mono, using library APIs directly in e2e.rs, or adding `--dump-ir` to `ail build`. The E2E stdout assertion already covers correctness; the IR-shape test would catch refactor regressions that rename mono symbols. - context: dropped from ct.4.4 when the BLOCKED condition surfaced. - [ ] **\[idea\]** Latency methodology rework — switch from per-run timing to a histogram-based approach so tail-latency regressions are visible without re-running. Queued from 21'g. - [ ] **\[idea\]** Parser-test backfill for 22b.4a-era duplicate-clause sites (class × 3, class method × 2, instance × 3, instance method × 1). No regression pin today; only worth it if a 22b.4a-era diagnostic needs to change. - context: surfaced in iter 22-tidy.7 (2026-05-10). - [ ] **\[idea\]** `write_type` `Type::Forall` arm in `crates/ailang-prose/src/lib.rs` silently drops constraints in inline-type rendering. Dormant — surface forms today only carry forall at fn-signature top level. Fix only if a future feature carries forall + constraints inline. - context: surfaced in iter 22-tidy.6 (2026-05-10). - [ ] **\[idea\]** Richer integration paths between RC and uniqueness — deferred from the 21' arc; revisit once the uniqueness inference covers more program shapes. - [ ] **\[idea\]** LLM tool-use schema / MCP server / LSP front-end over the prose-roundtrip cycle — additive layers on top of the static-prompt `ail merge-prose | client | ail parse | ail check` path (LLM calls back into `ail parse`/`ail check` mid-turn; an MCP-compatible client discovers AILang's resources/tools/prompts). Relocated here from DESIGN.md §"prose roundtrip" + PROSE_ROUNDTRIP.md by the docs-honesty-lint milestone (forward intent does not live in the canonical docs). - context: `docs/specs/2026-05-18-docs-honesty-lint.md` - [ ] **\[todo\]** Sweep 5 self-match anchor-exclusion — `bench/architect_sweeps.sh` Sweep 5's regex matches the DESIGN.md discriminator subsection's own forbidden-phrasing catalogue (L62 `"planned / will back / on the path to / if-when X arrives"`) forever, so the script inherits a guaranteed self-referential EXIT 1 the architect must re-adjudicate by hand each run. Not a new failure mode (Sweeps 1-4 already retain legitimate date-anchors; non-zero is advisory-by-design per the script header) — minor signal-erosion only. Optional fix: a negative-lookbehind / line-range exclusion so the rule's own example list is not a hit. P3 — may be cut; the architect adjudicates the single known self-match trivially today. - context: docs-honesty-lint audit commit (architect `[medium]` advisory wart, carry-on).