source: scrub iter-code / Decision-N residue from inline comments

Follow-up to bcd4181: the remaining ~530 inline `//` and `///`
comments still carrying opaque shorthand are now reformulated to
their content phrases. The only surviving `iter-<code>` reference
in source is the literal filename
`docs/journals/2026-05-13-iter-mq.3.md` (a real journal file).

Sweep covered:
  - `// Iter X.Y: <text>` prefixes (Iter 13a / 14a / 14e / 15g-aux /
    16b.x / 16d / 16e / 18b / 18c.x / 18d.x / 18e / 18g.x / 19a /
    19a.1 / 19b / 20a / 20f / 22-floats.x / 22b.x / 22c / 23.x /
    24.1 / cli-diag-human / hs.x / str-concat / etc.) — fully
    removed; the descriptive text that followed each prefix stays.
  - `// (Decision N)` and `per Decision N` and `Decision N axis 3` —
    replaced with the content phrase plus the relevant contract
    file (`design/contracts/tail-calls.md` for Decision 8,
    `design/contracts/memory-model.md` for Decision 10,
    `design/contracts/typeclasses.md` and `design/models/typeclasses.md`
    for Decision 11, `design/contracts/authoring-surface.md` for
    Decision 6, "the transitional dual-allocator" for Decision 9,
    "Effect prose" for Decision 3).
  - `// mq.X / mq.X (Task N) / mq.X journal / mq.X invariant` ->
    "the canonical-class-form rule / Class-class repurpose /
    method-dispatch-refactor journal / canonical-class-form
    invariant".
  - `// ct.X / ct.X (canonical-type-names) / ct.1.5a + ctt.2 /
    ct.2 Task N` -> "the canonical-form rule for type references /
    the canonical-form normalisation step / canonical-type-lookup
    refactor".
  - `// eob.X` -> "heap-Str-ABI" / "the Str carve-out".
  - `// rpe.X` -> "the per-type-print-op retirement".
  - `// post-mq.X / Pre-ct.X / pre-mq.X` -> "post-canonical-class-form" /
    "Pre-canonical-type-form" etc.
  - `/// Iter X regression: / /// Iter X.Y: / /// Iter A arm-close /
    /// Iter ct.4 (...): / /// Iter rpe.1 ...` -> descriptive
    phrases.

The journal filename in `crates/ailang-core/src/workspace.rs:573`
stays verbatim because it points at an actual file under
`docs/journals/`.

Tests: full `cargo test --workspace` green (80/80 test-result blocks
clean, no FAILED line). design_index_pin 5/5 + docs_honesty_pin 5/5
gating tests pass.

crates/ailang-codegen/src/synth.rs

@@ -28,7 +28,7 @@ pub(crate) fn llvm_type(t: &Type) -> Result<String> {
         // at the LLVM level. The actual signature travels via the
         // emitter's `ssa_fn_sigs` sidetable.
         Type::Fn { .. } => Ok("ptr".into()),
-        // Iter 13b: an unresolved rigid `Type::Var` reaching codegen is
+        // an unresolved rigid `Type::Var` reaching codegen is
         // a substitution bug. Earlier this silently lowered as `ptr`
         // (via the ADT fallback) and produced garbage IR; failing loudly
         // here surfaces the bug in the test suite.
@@ -56,11 +56,11 @@ pub(crate) fn fn_sig_from_type(t: &Type) -> Option<FnSig> {
     None
 }
 
-/// Iter 12b: AILang type of a builtin operator. Used by
+/// AILang type of a builtin operator. Used by
 /// `synth_arg_type` for arg-type inference at polymorphic call sites.
 /// Mirrors what the typechecker installs in its env via `builtins`.
 pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
-    // Iter 22-floats.3: same widening as `crates/ailang-check/src/
+    // same widening as `crates/ailang-check/src/
     // builtins.rs` — `+`/`-`/`*`/`/` and `!=`/`<`/`<=`/`>`/`>=` are
     // polymorphic. `%` stays monomorphic-Int. Codegen lowering for
     // these ops still goes through `builtin_binop` (Int-only) in
@@ -104,7 +104,7 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
         "+" | "-" | "*" | "/" => poly_a_a_to_a(),
         "%" => int_int_int(),
         "!=" | "<" | "<=" | ">" | ">=" => poly_a_a_to_bool(),
-        // Iter 16e: `==` is polymorphic — `forall a. (a, a) -> Bool`.
+        // `==` is polymorphic — `forall a. (a, a) -> Bool`.
         // The mono pipeline asks `synth_arg_type` for the actual arg
         // types at the call site; `lower_app` then dispatches to the
         // right LLVM instruction (icmp eq i64 / i1, @strcmp, or
@@ -130,14 +130,14 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
             param_modes: vec![],
             ret_mode: ParamMode::Implicit,
         },
-        // Iter 16d: `__unreachable__` is the polymorphic bottom value
+        // `__unreachable__` is the polymorphic bottom value
         // (`forall a. a`). Mirrors the typechecker's `builtins::install`.
         "__unreachable__" => Type::Forall {
             vars: vec!["a".into()],
             constraints: vec![],
             body: Box::new(Type::Var { name: "a".into() }),
         },
-        // Iter 22-floats.3: Float-conversion and inspection builtins.
+        // Float-conversion and inspection builtins.
         // Same lockstep with `crates/ailang-check/src/builtins.rs`.
         "neg" => Type::Forall {
             vars: vec!["a".into()],
@@ -199,7 +199,7 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
             param_modes: vec![],
             ret_mode: ParamMode::Implicit,
         },
-        // Iter 22-floats.3: Float bit-pattern constants. Bare values,
+        // Float bit-pattern constants. Bare values,
         // not fns — referenced via `Term::Var`. Mirrors the
         // typechecker's `builtins::install`. Codegen emits LLVM hex-
         // float literals at the use site in iter 4.
@@ -208,7 +208,7 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
     })
 }
 
-/// Iter 12b: AILang return type of a built-in effect op. The op's
+/// AILang return type of a built-in effect op. The op's
 /// param signature is irrelevant here since we only consume the ret.
 pub(crate) fn builtin_effect_op_ret(op: &str) -> Option<Type> {
     Some(match op {