test(grounding-tests) + feat(grounding-coercion-fold): Stratum A neg-path regressions; Examples 1–2 scratch fold (#1289 follow-up)

src/v3/grounding_coercion_fold/src/diagnostic.rs

@@ -9,12 +9,26 @@
 //!
 //! **Lockstep discipline:** any new variant added to substrate
 //! `EmissionDiagnostic` MUST land here as a parallel Rust mirror update.
+//!
+//! **Example 1 (scratch path):** design-emission-model §Example 1 names richer
+//! diagnostic fields (candidates, hints). Until the substrate carrier carries
+//! those structurally, the fold surfaces the **substrate-shaped** `UnderRefined`
+//! with `unspecified_axis: "bound"` only (axis matches the worked example).
 
-/// Rust mirror of substrate `EmissionDiagnostic` (subset; this crate
-/// only emits `FoldNotImplemented`). Variant-name lockstep enforced
-/// socially until reflection codegen retires the mirror.
+/// Rust mirror of substrate `EmissionDiagnostic` (subset; grows with substrate).
+///
+/// Practice 4 (`docs/modeling-discipline.md`): **🟡 YELLOW** — hand-maintained mirror until this
+/// lane consumes reflected substrate types (`.dag` → Rust enum codegen); dissolution aligns with
+/// #1216 / #1133 (no second authority for the same diagnostic facts — lockstep only).
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum EmissionDiagnostic {
+    /// Program intent or structural axis under-specified (substrate `UnderRefined`).
+    UnderRefined {
+        /// Mirrors substrate’s string axis payload for now. Scratch Example 1 only supplies
+        /// `"bound"`; when substrate grows structured axes (or this mirror gains a sum type),
+        /// replace free-form spelling here rather than widening implicit string conventions.
+        unspecified_axis: String,
+    },
     /// Full structural fold is not implemented; returning `Ok` would fabricate
     /// target choices (C-8 / `INVARIANTS.md`).
     FoldNotImplemented,

src/v3/grounding_coercion_fold/src/fold.rs

@@ -1,39 +1,70 @@
-//! Structural fold entry — **algorithm stub only**.
+//! Structural fold entry — coercion = emission (incremental body).
 //!
 //! ## Design authority (`docs/design-emission-model.md`)
 //!
-//! The eventual fold reads **program intent** + **substrate facts** (LanguageSpec rows,
-//! algebra inhabitance, lifetime facts, …) and returns either a **unique** target
-//! inhabitance per binding or a typed [`EmissionDiagnostic`](crate::diagnostic::EmissionDiagnostic).
-//! Worked **Examples 1–7** in that doc (e.g. unrefined `Int` → `UnderRefined`, bounded
-//! refinement → `u32`, `String` ownership cases, algebra ambiguity, no-inhabitant,
-//! cross-target portability sketches) are the **behavioral targets** for the future
-//! implementation — **not** implemented in this crate yet.
+//! Worked **Examples 1–7** in that doc are behavioral targets. **Examples 1–2** are
+//! implemented for the [`LanguageSpecProjection::ScratchIntExamples`](crate::types::LanguageSpecProjection::ScratchIntExamples)
+//! checkpoint path only; other examples and `Undeclared` remain
+//! [`EmissionDiagnostic::FoldNotImplemented`](crate::diagnostic::EmissionDiagnostic::FoldNotImplemented).
 //!
-//! ## Gates (dispatch)
-//!
-//! Full body is gated on T-Ground-LanguageSpec row work post-#1227 and lifetime /
-//! substrate boundary metadata (#1130). This module only enforces the **public
-//! signature** and **fail-closed** stub (`FoldNotImplemented`).
+//! **Call-site (ScratchIntExamples):** While the scratch body ignores `dag` / lifetime inputs and
+//! fixes [`BindingId`](v3_grounding_lifetime::BindingId)`(0)`, production wiring must not treat
+//! returned map keys as evidence of real program bindings (#1133 / #1286).
 
 use std::collections::BTreeMap;
 
 use v3_compiler::dag::Dag;
 use v3_grounding_lifetime::{BindingId, LifetimeAnalysisReport};
 
 use crate::diagnostic::EmissionDiagnostic;
-use crate::types::{LanguageSpecProjectionUndeclared, TargetInhabitance};
+use crate::types::{IntScratchExample, LanguageSpecProjection, TargetInhabitance};
+
+fn fold_design_doc_example_1_unrefined_int() -> Result<TargetInhabitance, EmissionDiagnostic> {
+    Err(EmissionDiagnostic::UnderRefined {
+        unspecified_axis: "bound".to_string(),
+    })
+}
+
+fn fold_design_doc_example_2_semiring_u32() -> Result<TargetInhabitance, EmissionDiagnostic> {
+    Ok(TargetInhabitance::RustU32)
+}
 
-/// Structural fold: program + lifetime analysis + (future) LanguageSpec projection →
+/// Structural fold: program + lifetime analysis + LanguageSpec projection →
 /// per-binding target inhabitances, **or** a single typed diagnostic.
 ///
-/// Today: **always** [`EmissionDiagnostic::FoldNotImplemented`](EmissionDiagnostic::FoldNotImplemented)
-/// (C-8). Parameters are accepted so call sites compile against the eventual shape;
-/// they are intentionally unused until the fold body lands.
+/// - [`LanguageSpecProjection::Undeclared`](crate::types::LanguageSpecProjection::Undeclared): fail-closed
+///   [`EmissionDiagnostic::FoldNotImplemented`](crate::diagnostic::EmissionDiagnostic::FoldNotImplemented).
+/// - [`LanguageSpecProjection::ScratchIntExamples`](crate::types::LanguageSpecProjection::ScratchIntExamples): runs
+///   design-doc Examples 1–2 for a single synthetic binding [`BindingId`](v3_grounding_lifetime::BindingId)`(0)`.
+///   **Checkpoint:** ignores `_dag` by design; on the scratch path, `lifetime_facts` must be
+///   empty in debug builds until this body reads real facts. Do not widen this arm to multiple
+///   bindings or real program facts without landing the declared projection / dissolution path
+///   first (#1133 / #1286).
 pub fn fold_program_to_target(
     _dag: &Dag,
-    _lifetime_facts: &LifetimeAnalysisReport,
-    _language_spec: &LanguageSpecProjectionUndeclared,
+    lifetime_facts: &LifetimeAnalysisReport,
+    language_spec: &LanguageSpecProjection,
 ) -> Result<BTreeMap<BindingId, TargetInhabitance>, EmissionDiagnostic> {
-    Err(EmissionDiagnostic::FoldNotImplemented)
+    match language_spec {
+        LanguageSpecProjection::Undeclared => {
+            let _ = lifetime_facts;
+            Err(EmissionDiagnostic::FoldNotImplemented)
+        }
+        LanguageSpecProjection::ScratchIntExamples(example) => {
+            debug_assert!(
+                lifetime_facts.is_empty(),
+                "ScratchIntExamples checkpoint: pass an empty LifetimeAnalysisReport until this body reads facts (#1133 / #1286)"
+            );
+            let binding = BindingId(0);
+            let inhabitance = match example {
+                IntScratchExample::DesignDocExample1UnrefinedInt => {
+                    fold_design_doc_example_1_unrefined_int()?
+                }
+                IntScratchExample::DesignDocExample2BoundedU32 => {
+                    fold_design_doc_example_2_semiring_u32()?
+                }
+            };
+            Ok(BTreeMap::from([(binding, inhabitance)]))
+        }
+    }
 }

src/v3/grounding_coercion_fold/src/lib.rs

@@ -1,43 +1,34 @@
-//! T-Ground-Coercion-Fold — **consumer-side scaffold** for the structural emission fold.
+//! T-Ground-Coercion-Fold — structural emission fold (**coercion = emission**).
 //!
-//! Per [`docs/design-emission-model.md`](../../../../docs/design-emission-model.md) lane table
-//! (~381–384), this lane is the mechanical **coercion = emission** fold: read program
-//! intent + substrate facts, return a unique target inhabitance per binding or
-//! [`EmissionDiagnostic`](diagnostic::EmissionDiagnostic). It **replaces** the retracted
-//! T-Ground-Engine framing (no separate coercion engine).
+//! Per [`docs/design-emission-model.md`](../../../../docs/design-emission-model.md), this lane
+//! reads program intent + substrate facts and returns a unique target inhabitance per binding
+//! or [`EmissionDiagnostic`](diagnostic::EmissionDiagnostic).
 //!
-//! ## Algorithm-shape (stub)
+//! ## Implemented today
 //!
-//! - [`fold_program_to_target`](fold::fold_program_to_target) is the public entry matching
-//!   the manager dispatch shape: [`v3_compiler::dag::Dag`], [`v3_grounding_lifetime::LifetimeAnalysisReport`],
-//!   and [`types::LanguageSpecProjectionUndeclared`] (open carrier — **do not** guess final
-//!   LanguageSpec projection).
-//! - Until LanguageSpec + Dag boundary work land, the fold **fail-closed** returns
-//!   [`EmissionDiagnostic::FoldNotImplemented`](diagnostic::EmissionDiagnostic::FoldNotImplemented)
-//!   for all inputs (C-8).
-//!
-//! ## Worked examples (targets for future implementation; not implemented here)
-//!
-//! Authoritative walkthroughs live in [`docs/design-emission-model.md`](../../../../docs/design-emission-model.md)
-//! **§Worked examples** — including at minimum **Example 1** (unrefined `Int` → fail-closed
-//! diagnostic), **Example 2** (`Int(0..2^32)` → Rust `u32`), **Examples 3–4** (`String`
-//! ownership / lifetime), **Example 5** (algebra ambiguity), **Example 6** (`NoInhabitant`),
-//! and **Example 7** / cross-target sketches tied to Modeling problem 7. This crate’s
-//! rustdoc on [`fold`](crate::fold) cites the same authority without duplicating payloads.
+//! - [`fold_program_to_target`](fold::fold_program_to_target) with
+//!   [`LanguageSpecProjection::Undeclared`](types::LanguageSpecProjection::Undeclared) stays
+//!   fail-closed [`EmissionDiagnostic::FoldNotImplemented`](diagnostic::EmissionDiagnostic::FoldNotImplemented).
+//! - [`LanguageSpecProjection::ScratchIntExamples`](types::LanguageSpecProjection::ScratchIntExamples)
+//!   drives **design-emission-model §Example 1** (unrefined `Int` → substrate-shaped
+//!   [`EmissionDiagnostic::UnderRefined`](diagnostic::EmissionDiagnostic::UnderRefined) with axis `"bound"`)
+//!   and **§Example 2** (`Int(0..2^32)` / `Semiring` exact-bound → [`TargetInhabitance::RustU32`](types::TargetInhabitance::RustU32))
+//!   for a single synthetic binding — checkpoint until a real LanguageSpec projection replaces
+//!   the scratch carrier (manager #1133 / #1286).
 //!
 //! ## SG-0 / discipline
 //!
 //! - **No** edits under [`src/v3/compiler/`](../../compiler) — consume `v3-compiler` APIs only.
-//! - Lane-local [`EmissionDiagnostic`](diagnostic::EmissionDiagnostic) mirrors the Lifetime-Analyzer
-//!   pattern; converges on substrate carrier per `docs/briefs/t-ground-diagnostic.md` / #1216.
+//! - Lane-local [`EmissionDiagnostic`](diagnostic::EmissionDiagnostic) converges per
+//!   `docs/briefs/t-ground-diagnostic.md` / #1216.
 
 mod diagnostic;
 mod fold;
 mod types;
 
 pub use diagnostic::EmissionDiagnostic;
 pub use fold::fold_program_to_target;
-pub use types::{LanguageSpecProjectionUndeclared, TargetInhabitance};
+pub use types::{IntScratchExample, LanguageSpecProjection, TargetInhabitance};
 
 #[cfg(test)]
 mod tests {
@@ -47,11 +38,42 @@ mod tests {
     use super::*;
 
     #[test]
-    fn fold_stub_fail_closed_fold_not_implemented() {
+    fn fold_undeclared_projection_stays_fold_not_implemented() {
         let dag = Dag::new();
         let lifetime: LifetimeAnalysisReport = Default::default();
-        let spec = LanguageSpecProjectionUndeclared;
-        let err = fold_program_to_target(&dag, &lifetime, &spec).expect_err("stub");
+        let spec = LanguageSpecProjection::Undeclared;
+        let err = fold_program_to_target(&dag, &lifetime, &spec).expect_err("undeclared");
         assert_eq!(err, EmissionDiagnostic::FoldNotImplemented);
     }
+
+    #[test]
+    fn design_doc_example_1_unrefined_int_under_refined() {
+        let dag = Dag::new();
+        let lifetime: LifetimeAnalysisReport = Default::default();
+        let spec = LanguageSpecProjection::ScratchIntExamples(
+            IntScratchExample::DesignDocExample1UnrefinedInt,
+        );
+        let err = fold_program_to_target(&dag, &lifetime, &spec).expect_err("under-refined");
+        assert_eq!(
+            err,
+            EmissionDiagnostic::UnderRefined {
+                unspecified_axis: "bound".to_string(),
+            }
+        );
+    }
+
+    #[test]
+    fn design_doc_example_2_bounded_int_emits_rust_u32() {
+        let dag = Dag::new();
+        let lifetime: LifetimeAnalysisReport = Default::default();
+        let spec = LanguageSpecProjection::ScratchIntExamples(
+            IntScratchExample::DesignDocExample2BoundedU32,
+        );
+        let got = fold_program_to_target(&dag, &lifetime, &spec).expect("ok");
+        assert_eq!(got.len(), 1);
+        assert_eq!(
+            got.get(&v3_grounding_lifetime::BindingId(0)),
+            Some(&TargetInhabitance::RustU32)
+        );
+    }
 }

src/v3/grounding_coercion_fold/src/types.rs

@@ -1,17 +1,43 @@
-//! Open / stub carriers for the public fold signature until LanguageSpec + lowering land.
+//! LanguageSpec projection + target inhabitance carriers for the structural fold.
 
-/// Placeholder for the structural **LanguageSpec** projection the fold will consume.
+/// How the fold obtains LanguageSpec / target-primitive substrate facts.
 ///
-/// **Shape TBD** — manager dispatch (#1203 / #1133): substrate may declare a projection
-/// carrier, or the fold may walk [`v3_compiler::dag::Dag`] directly. **Do not** treat this
-/// type as the final API. No row consumption until LanguageSpec Phase 1.5 (#1227) and
-/// related substrate gates land.
-#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
-pub struct LanguageSpecProjectionUndeclared;
+/// Practice 4 (`docs/modeling-discipline.md`): **🟡 YELLOW** — `Undeclared` awaits a declared
+/// LanguageSpec projection; `ScratchIntExamples` is an interim checkpoint. Named dissolution:
+/// #1133 / #1286 (declared projection replaces this carrier).
+///
+/// **`Undeclared`** — production entry stays fail-closed until a real projection lands
+/// (substrate / #1286 / manager #1133).
+///
+/// **`ScratchIntExamples`** — **checkpoint only**: drives [`docs/design-emission-model.md`](../../../../docs/design-emission-model.md)
+/// **Example 1** and **Example 2** without walking Phase 1 Dag rows. Remove or supersede when
+/// a declared projection replaces this scratch path.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
+pub enum LanguageSpecProjection {
+    #[default]
+    Undeclared,
+    ScratchIntExamples(IntScratchExample),
+}
+
+/// Scratch selector aligned to design-emission-model §Worked examples (Int only).
+///
+/// Practice 4 (`docs/modeling-discipline.md`): **🟡 YELLOW** — bounded to Examples 1–2 only;
+/// superseded when a declared projection generalizes Int examples (#1133 / #1286).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum IntScratchExample {
+    /// Example 1 — `data x: Int = 0` → `EmissionDiagnostic::UnderRefined`.
+    DesignDocExample1UnrefinedInt,
+    /// Example 2 — `data count: Int(0..2^32) = 100` → unique Rust `u32`.
+    DesignDocExample2BoundedU32,
+}
 
-/// Stub for **unique per-binding target inhabitance** (primitive + refinement witness).
+/// Unique target inhabitance for a binding (Examples 1–2 surface only).
 ///
-/// Populated by the real Coercion-Fold body when T-Ground-LanguageSpec + extraction
-/// gates unblock; the scaffold never returns `Ok` with populated values.
-#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct TargetInhabitance;
+/// Practice 4 (`docs/modeling-discipline.md`): single-variant placeholder — N \< 2, so no 🟢/🟡/🔴
+/// coproduct checkpoint until a second inhabitant is introduced. When a second variant lands,
+/// classify this enum explicitly (substrate vs Rust mirror / dissolution) — do not grow ad hoc
+/// without the same checkpoint discipline as the projection carriers.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum TargetInhabitance {
+    RustU32,
+}