journal: ct.2 typechecker cleanup

docs/JOURNAL.md

@@ -14222,3 +14222,88 @@ Workspace at iter-ct.1 close: full `cargo test --workspace` green
 the three regression scripts not re-run for this iter (no codegen-
 shape change to existing fixtures beyond the surgical migration;
 they run at canonical-type-names milestone close after ct.4).
+
+## 2026-05-11 — Iteration ct.2: typechecker cleanup
+
+Three tasks landed in the canonical-type-names milestone's
+typechecker-cleanup iteration, plus targeted follow-ups driven by
+the quality-review pass.
+
+- **ct.2.1** (`78ccbce`): wired `qualify_local_types` into the
+  `env.class_methods` channel of `Term::Var` resolution, closing
+  the last cross-module fn-lookup boundary that did not run the
+  qualifier. The motivating shape: prelude declares
+  `class Ord a` with `compare : a -> a -> Ordering`; the method's
+  `Ordering` is bare-local to prelude; without the qualifier on
+  the class-method channel, a consumer module sees bare
+  `Ordering` and its pattern match against the post-ct.1
+  canonical `prelude.Ordering` scrutinee no longer resolves.
+  Also fixed a latent gap in `qualify_local_types`'s
+  `Type::Forall` arm: it now recurses into `constraints[].type_`,
+  symmetric to the ct.1.5a-followup fix on
+  `normalize_type_for_registry`. Two new tests pin both
+  invariants.
+- **ct.2.2** (`b3c3b60` + followups `0ca5b3d`, `0044467`,
+  `edb694f`): deleted the `Pattern::Ctor` imports-fallback (iter
+  15a); replaced with type-driven lookup keyed on
+  `expected: Type::Con`'s canonical name. The lookup no longer
+  consults `env.ctor_index`; the per-module overlay now serves
+  only duplicate-detection at workspace build. The
+  `cross_module_pat_ctor_ambiguous_errors` test deleted
+  (ambiguity unreachable post-refactor; lookup is anchored to a
+  single TypeDef). The `CheckError::AmbiguousCtor` variant +
+  its `ambiguous-ctor` diagnostic code deleted as dead code
+  (quality-review pushed back on leaving it as
+  dead-but-defensive — the project rule is "no backwards-compat
+  shims for removed features"). The now-unused `Bag` test
+  fixture in `cross_module_ws` removed in `0044467`. Doc
+  comments on `UnknownCtorInPattern` and
+  `mono_xmod_ctor_pattern.rs` refreshed in `edb694f` to describe
+  the post-ct.2 mechanism. The `mono_xmod_ctor_pattern.rs`
+  regression test still passes — its scrutinee carries the
+  qualified type and the new lookup finds the TypeDef directly.
+- **ct.2.3** (`97bb5e7`): deleted the `Term::Ctor` synth
+  imports-fallback (iter 23.1.3). Bare cross-module `type_name`
+  now fails closed with `UnknownType`; the post-ct.1 workspace
+  validator catches the shape at load time for canonical inputs.
+  The `CheckError::AmbiguousType` variant deleted (symmetric to
+  the `AmbiguousCtor` cleanup; same dead-code reasoning). Two
+  tests deleted (`cross_module_term_ctor_ambiguous_type_errors`
+  and `user_module_can_pattern_match_on_prelude_ordering_bare`
+  — both pinned behaviour that ct.2 removes); two tests added
+  (`ct2_term_ctor_bare_cross_module_fails_closed` and
+  `ct2_term_ctor_qualified_cross_module_resolves`).
+
+Remaining obsolete mechanisms (ct.3 scope): the codegen
+`lookup_ctor_by_type` imports-fallback (iter 23.1.4) and the
+mono `apply_per_module_ctor_index_overlay` (iter 23.2 fix
+`84dcc46`). Surviving stale doc-comments at
+`crates/ailang-codegen/src/lib.rs:1748` and
+`crates/ail/src/main.rs:239` reference the now-removed
+`AmbiguousType` / `AmbiguousCtor` paths; ct.3 (codegen) and
+ct.4 (the migrate-canonical-types subcommand may itself retire
+as one-shot tooling) will tidy those when the surrounding code
+changes.
+
+Lesson from ct.2.2 quality review: the orchestrator's plan
+explicitly said "leave `CheckError::AmbiguousCtor` as
+dead-but-defensive, defer to a later tidy". The quality
+reviewer correctly pushed back, citing CLAUDE.md's
+"Avoid backwards-compatibility hacks like renaming unused
+\_vars, re-exporting types, adding `// removed` comments for
+removed code, etc. If you are certain that something is unused,
+you can delete it completely." Lesson logged for future plan
+writing: when an enum variant becomes unused as a result of
+the iter's own changes, the delete belongs in the same iter,
+not a later tidy. The roadmap was updated implicitly — both
+variants are now gone, no roadmap entry needed.
+
+Workspace at iter-ct.2 close: full `cargo build --workspace` and
+`cargo test --workspace` green (451 tests, 0 failed). Bench
+scripts not re-run (no codegen-shape change, no fixture
+migration this iter). E2E coverage skipped per implement-skill
+carve-out (ct.2 ships internal refactor only; per-task pin
+tests + the existing workspace test surface cover the
+invariants; the canonical E2E demonstration of the
+iter-23.3-Task-4 bug closure happens in ct.4 with the recreated
+`compare_primitives_smoke.ail.json` fixture).