AILang/docs/roadmap.md

# 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, a branch is open, or commits are
  landing); `- [x]` is done. A finished entry may stay briefly for
  context, then is removed (with a one-line mirror in
  `docs/journals/`).
- Each entry is tagged by **kind** and lives under a **priority**
  bucket:
  - **\[milestone\]** — big chunk that will get a `docs/specs/<milestone>.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 journal entry (per-iter
  file under `docs/journals/` or, for pre-2026-05-11 entries, the
  archived `docs/journal-archive.md`) where the rationale lives.
  The roadmap is intentionally terse; rationale stays in the
  journals.
- 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

_(empty — prelude-decouple milestone closed 2026-05-14, audit-pd
clean. Pick the next milestone from P2.)_

## P1 — Next

- [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`; per-iter
    journals 2026-05-12-iter-24.1, 2026-05-13-iter-24.2, 2026-05-13-iter-24.3.

## P2 — Medium-term

- [ ] **\[milestone\]** 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) and
    `docs/journals/2026-05-15-iter-it.3.md` (the branching-builder
    counter-example that surfaced the gap).

- [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: per-iter journal `docs/journals/2026-05-14-iter-rpe.1.md`.

- [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: JOURNAL 2026-05-09
  - 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: JOURNAL 2026-05-10 ("Audit close: env-construction unify"); 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: per-iter journal `docs/journals/2026-05-14-iter-cli-diag-human.md`.
- [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: JOURNAL 2026-05-11 ("Iteration ct.1"); 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<String, String>` 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: JOURNAL 2026-05-11 ("Iteration ct.1") — flagged by 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: JOURNAL 2026-05-09
- [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 `<module>.<Class>.<method>` 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: JOURNAL pre-22, "Boehm transitional"
- [ ] **\[feature\]** 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.

- [ ] **\[todo\]** `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: JOURNAL 2026-05-10 ("Audit close: design-md-consolidation").
- [ ] **\[todo\]** `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: JOURNAL 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 <owner>)` 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). Decide: accept `(app f)` as the nullary-call
  surface, or ratify in DESIGN.md that nullary functions are
  expressed differently (and say how). 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.
- [ ] **\[todo\]** 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.
- [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: JOURNAL 2026-05-11 ("Iteration ct.4") — 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: per-iter journal 2026-05-13-iter-str-concat.md.

- [~] **\[milestone\]** 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).

  **Progress.** Decomposed at brainstorm time (2026-05-15) into a
  sequence of shippable sub-milestones. Sub-milestone 1 closed
  2026-05-15: **mut-local** — sealed-by-construction `mut`/`var`/
  `assign` blocks for Int/Float/Bool/Unit scalars, alloca-resident,
  no escape, no `!Mut` effect leakage. Foundation in place;
  fn signatures stay pure while LLM authors can write imperative
  accumulators directly. Spec `docs/specs/2026-05-15-mut-local.md`;
  iters mut.1/mut.2/mut.3/mut.4-tidy (commits 7b92719, b24718a,
  03fb633, 20add51). Remaining sub-milestones (to be brainstormed
  separately, in order): (2) effect-handler infrastructure as a
  prerequisite for any non-IO/non-Diverge effect; (3) `!Mut` effect
  + `ref a` first-class type that can escape mut blocks under
  uniqueness-tracking; (4) mutable-array primitive `MutArray a`;
  (5) `Stateful a b` sealed callable type + `pipe` combinator with
  zero-allocation composition + `runST`-equivalent escape discharge.

  **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: the "Iteration
    discipline" P1 milestone supersedes the earlier "while-loops
    legal" scope here — repetition is structural recursion or named
    `loop`/`recur`, never a `while` 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/<date>-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: JOURNAL 2026-05-11 ("Iteration ct.3" + ct.4 close).
- [ ] **\[todo\]** `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: JOURNAL 2026-05-11 ("Iteration ct.4") — 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: JOURNAL 2026-05-10 ("Iteration 22-tidy.7")
- [ ] **\[idea\]** `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: JOURNAL 2026-05-10 ("Iteration 22-tidy.6")
- [ ] **\[idea\]** Richer integration paths between RC and
  uniqueness — deferred from the 21' arc; revisit once the
  uniqueness inference covers more program shapes.