R2 Grounding Manager — post-pilot bundle (Engine brief + receipt + Director escalation + working-state)

docs/briefs/grounding-manager.md

@@ -1,11 +1,14 @@
 # R2 Grounding Manager Brief
 
-**Status:** `PROPOSAL` — pending R2 proposal
-([`docs/r2-structure.md`](../r2-structure.md), PR #754) merge +
-R1 all-gates-green closure. Until then, this brief is the R2
-Grounding Manager's scope-in-preparation; it does not dispatch
-work. On R2 promotion, the `PROPOSAL` banner lifts and this brief
-becomes the live dispatch authority for the lane.
+**Status:** `PROPOSAL` (formal) → `ACTIVE` (Director-discretionary).
+Formal R2 promotion still pending R1 all-gates-green closure +
+[`docs/r2-structure.md`](../r2-structure.md) promotion to ROADMAP.
+Director-discretionary dispatch has been used since 2026-04-25 for
+T-Ground-Pilot (PR #765, merged) and T-Ground-Engine-Phase-1 audit
+(PR #768, merged). Engine implementation parked pending the loader-close
+PR (Director routed Route 1 on 2026-04-25; substrate ask is in flight as
+ad-hoc Director dispatch) — see [`t-ground-engine-substrate-escalation.md`](t-ground-engine-substrate-escalation.md).
+Working state at the bottom of this brief reflects current dispatch state.
 
 ## Orient before reading
 
@@ -248,11 +251,11 @@ to director before dispatching full-reference work.
 
 Lane-owner dispatch status (update as sub-deliverables close):
 
-**T-Ground-Pilot:**
-- [ ] Rust primitive `.dag` declarations (i8–i64, u8–u64, bool, Unit)
-- [ ] Toy inhabitance-search engine
-- [ ] Routing-stability tests against pilot set (parity with current table)
-- [ ] Pilot receipt document
+**T-Ground-Pilot:** ✅ COMPLETE (PR #765 merged 2026-04-25 commit `2909f9e05`; receipt in [`grounding-pilot-receipt.md`](grounding-pilot-receipt.md))
+- [x] Rust primitive `.dag` declarations (i8–i64, u8–u64, bool, Unit)
+- [x] Toy inhabitance-search engine
+- [x] Routing-stability tests against pilot set (parity with current table)
+- [x] Pilot receipt document
 
 **T-Ground-Rust:**
 - [ ] Numeric types (integer, float, character)
@@ -278,11 +281,12 @@ Lane-owner dispatch status (update as sub-deliverables close):
 - [ ] Array, slice, map, struct, pointer
 - [ ] Function, interface, channel
 
-**T-Ground-Engine:**
-- [ ] Inhabitance-search walker
-- [ ] Minimum-satisfier selection
-- [ ] Fail-closed tie-breaking with structured diagnostic
-- [ ] Cross-type coercion paths (e.g., UTF-8 `Char ↔ u8`)
+**T-Ground-Engine:** ⏸️ PARKED — Phase 0 substrate audit complete (PR #768 merged 2026-04-25 commit `4afc0d794`); Director routed Route 1 (small loader-close, ad-hoc Director dispatch). Engine re-dispatches in sharpened-(b) form once the loader-close PR merges. See [`t-ground-engine-substrate-escalation.md`](t-ground-engine-substrate-escalation.md).
+- [x] Phase 0 substrate audit (concluded escalation-class)
+- [ ] Inhabitance-search walker (Phase 1, blocked on loader-close PR)
+- [ ] Minimum-satisfier selection (Phase 1)
+- [ ] Fail-closed tie-breaking with structured diagnostic (Phase 1; pilot established the contract baseline)
+- [ ] Cross-type coercion paths (e.g., UTF-8 `Char ↔ u8`) (Phase 2; blocks on full-reference)
 
 **T-Ground-Tests:**
 - [ ] Routing-stability TestClaim variant declared
@@ -299,16 +303,30 @@ Lane-owner dispatch status (update as sub-deliverables close):
 - [ ] Remove `TypeRealization.carrier: String` field from `src/v3/std/emit_model.dag`
 - [ ] Remove emit-pipeline call sites reading the old surface
 - [ ] All test claims assert against the new structural authority (no residual reads of deleted scaffolding)
+- [ ] Delete `src/v3/grounding_pilot/` workspace member (scope-expansion confirmed in PR #765)
+- [ ] Delete Engine sibling crate if Route 1/3 dispatched as (b.i) (scope-expansion contingent on Director routing)
 - [ ] Track 13 closure PR lands — single step
 
 Decisions log (append as they happen):
 
-- _(none yet)_
+- **2026-04-25** — Pilot dispatched and merged under Director-discretionary dispatch (R2 promotion gates not yet formally fired). PR #765.
+- **2026-04-25** — Pilot lessons synthesized into [`grounding-pilot-receipt.md`](grounding-pilot-receipt.md). Five carry-forwards: Stratum-B finding, mirroring-as-substrate-ask, fail-closed contract baseline, SG-0 location reasoning, state-space discipline as full-reference precedent.
+- **2026-04-25** — Pilot's `RustPrimitive` partition (`IntegerPrimitive | NonIntegerPrimitive`) locked as full-reference precedent shape via codex P2 adjudication. Future widening to flat record is out of scope.
+- **2026-04-25** — Engine-Phase-1 brief landed (PR #767, `t-ground-engine-phase-1.md`). Audit-first discipline; no Rust-constant mirroring; variant-aware walker; SG-0 untouched.
+- **2026-04-25** — Engine-Phase-1 Phase 0 audit landed (PR #768, `t-ground-engine-substrate-audit.md`). Conclusion: both options (a) and (b) block on the same substrate gaps; escalation-class. Engine implementation parked.
+- **2026-04-25** — Engine substrate ask escalated to Director via [`t-ground-engine-substrate-escalation.md`](t-ground-engine-substrate-escalation.md). Manager recommended Route 3: route Gap 1 close through Pure Bootstrap to Zero program (PB-1 / PB-Bootstrap-Process scope overlap). *(Past tense — overruled in next entry.)*
+- **2026-04-25** — Director chose **Route 1** (small loader-close, ad-hoc Director dispatch). Manager recommendation overruled with substantive reasoning: PB-1 migrates *existing* fixture sets; deciding the bootstrap shape includes a new fifth set is upstream of PB-1's pattern. Faster unblock: sharpened (b) Engine within days vs quarters for full Pure Bootstrap to Zero scope. Manager internalized the upstream-vs-pattern distinction for future cross-manager flagging.
 
 Open questions for director:
 
-- _(none yet — program is pre-dispatch)_
+- ~~**Engine substrate routing**~~ — RESOLVED 2026-04-25. Route 1 chosen by Director.
+- **R2 promotion timing** — formally still PROPOSAL pending R1 all-gates-green closure. R1 Census Close landed (PR #763) but Director-discretionary dispatch has been used for Pilot + Engine-Phase-1-audit. Consider formalizing the promotion or making the discretionary mode explicit in `r2-structure.md`. **See Tracked debt below.**
+
+Tracked debt (manager surfaces, Director resolves):
+
+- **Dual-status convention (`PROPOSAL` formal / `ACTIVE` discretionary).** Currently load-bearing for two dispatched lanes (Pilot, Engine-Phase-1 audit) and likely a third (loader-close → Engine re-dispatch). **Owner**: Director. **Forcing function**: if this convention survives one more dispatch (i.e., loader-close lands and Engine re-dispatches under it), manager surfaces as escalation rather than queued open-question — the cost of dual-authority dispatch state grows non-linearly past three live dispatches per `feedback_state_space_vs_behavioral_invariants` (status as an enum-with-implicit-modes admits illegal combinations like "PROPOSAL but ACTIVE"). **Resolution paths** (Director picks one): (a) formalize R2 promotion explicitly via `r2-structure.md` amendment; (b) add a "Director-discretionary dispatch" mode to `r2-structure.md` as a first-class status alongside PROPOSAL/ACTIVE; (c) defer formalization with explicit "do not let this accumulate" sunset commitment.
 
 Cross-manager notifications queued:
 
-- _(none yet — awaits R1 close + substrate-capability closure signals from Surface and Testgen Managers)_
+- ~~**Pure Bootstrap to Zero Manager** (PR #766) — substrate ask~~ — Director chose Route 1 (ad-hoc dispatch, not routed through Zero-Floor). Director handles Zero-Floor heads-up directly per cross-program coordination. No manager-side notification queued.
+- **Surface / Testgen Managers** (R1, archived on R1 close per `r2-structure.md`) — pilot's fail-closed-by-construction shape (`GroundingError::{Ambiguous, NoInhabitant}`) is general-purpose, not Grounding-specific. If their wind-down work hasn't closed yet, this shape is reusable as a contract baseline.

docs/briefs/grounding-pilot-receipt.md

@@ -0,0 +1,109 @@
+# T-Ground-Pilot — Receipt
+
+**Status**: COMPLETE. Pilot lane closed via [PR #765](https://github.com/gunb-ai/gunbc/pull/765) (merged commit `2909f9e05`, 2026-04-25).
+
+**Purpose**: capture the lessons the pilot established empirically, so they carry forward into Engine + full-reference + Dissolve scopes without requiring future workers to re-derive them from the PR thread. Manager-authored synthesis per the [grounding-manager brief](grounding-manager.md) ("Pilot deliverable #4 — manager scope, not worker scope").
+
+**Audience**: T-Ground-Engine workers (any phase), T-Ground-Rust / -Python / -Go workers (when substrate unblocks), T-Ground-Tests workers, R2 Grounding Manager (working-state inputs), Director (program-scope review).
+
+---
+
+## Framing question the pilot answered
+
+*Does inhabitance-search routing — consuming structural target-primitive declarations and selecting by algebra-homomorphism — produce the same target-primitive selection as today's name-keyed table lookup, on a small Rust pilot set?*
+
+**Answer**: Yes, with a finding. Routing parity stratifies into two strata:
+
+- **Stratum A** (3 of 10 pilot types — `Int(=Int64)→i64`, `Bool→bool`, `Unit→()`): exact match against today's `rust_type_checkpoints`.
+- **Stratum B** (7 of 10 — `Int8/16/32`, `UInt8`–`UInt64`): engine produces canonical width-correct primitive that the name-keyed table cannot reach. The fallback `OrderedRing→i64` algebra-inhabitant is width-blind (would mis-route `Int8` to `i64`); `Semiring` has no inhabitant declared at all (unsigned types fail-closed today).
+
+The proposal's central architectural claim — *structural `(algebra, carrier)` matching strictly subsumes name-keyed lookup* — was empirically demonstrated. The proposal did not need amendment.
+
+---
+
+## The five lessons
+
+These are the carry-forwards. Each cites its empirical source (the PR commit or comment that produced it) and names where the lesson routes forward.
+
+### Lesson 1 — Stratum-B finding: full-reference scope is larger than implicit baseline
+
+**What we learned.** Today's table-driven coercion surface (`dsl/extdeps/languages/rust/types.dag`'s `rust_type_checkpoints` + `rust_algebra_inhabitants`) covers far less than the implicit baseline assumed. Of the 10 pilot types, only 3 have name-keyed routing entries; 7 either mis-route via width-blind fallbacks or fail-closed entirely.
+
+**Source.** [PR #765 body — "Parity finding (pilot-success signal, not an escalation)"](https://github.com/gunb-ai/gunbc/pull/765); [LGTM comment 4317308089](https://github.com/gunb-ai/gunbc/pull/765#issuecomment-4317308089).
+
+**Forward routing.** T-Ground-Rust / -Python / -Go workers and brief authors must internalize: *the full-reference lanes' true scope is "model the language reference's primitives" + "extend routing onto previously fail-closed surface."* The latter is invisible from the existing tables — it only becomes visible by enumerating the language reference and discovering what's missing. Brief authors for the full-reference lanes should not size scope by counting existing table rows.
+
+**Forward routing (T-Ground-Dissolve).** Dissolution doesn't just swap table-routing for engine-routing on covered surface — it also extends routing onto previously fail-closed surface. The dissolution PR is a strict-superset behavior change, not a like-for-like swap.
+
+### Lesson 2 — Mirroring is forbidden; eliminating it is a substrate ask
+
+**What we learned at pilot time.** The pilot's Rust-constant mirror of `dsl/extdeps/languages/rust/primitives.dag` (and of `dsl/std/integer.dag`'s type-mappings) is a load-bearing concession with hand-sync risk. The lesson, as originally written: *Engine's load-bearing scope is to consume `.dag` declarations directly, eliminating the mirror.*
+
+**What the audit revealed (post-pilot).** The mirror existed precisely because the v3 substrate doesn't load `dsl/extdeps/languages/*` into the bootstrap Dag at all (`bootstrap.rs:16-19` — *"Production bootstrap does not inject target-language realizations"*). The pilot's choice to mirror was forced by the substrate, not by pilot-scope convenience. Eliminating the mirror is a **substrate-capability question**, not an Engine-internal question.
+
+**Source.** Pilot mirroring discipline first articulated in [PR #765 LGTM comment 4317308089](https://github.com/gunb-ai/gunbc/pull/765#issuecomment-4317308089); substrate dependency confirmed in [the Phase 0 audit](t-ground-engine-substrate-audit.md) (PR #768 merged 2026-04-25).
+
+**Forward routing.** Engine cannot honor "no mirroring" without the extdeps loader closing. See `docs/briefs/t-ground-engine-substrate-escalation.md` for the routing decision.
+
+**Forward routing (full-reference lanes).** Same constraint: T-Ground-Python / -Go cannot consume their respective `dsl/extdeps/languages/*/primitives.dag` files without the extdeps loader. Their dispatch shape depends on the same substrate close.
+
+### Lesson 3 — Fail-closed by construction is the contract baseline
+
+**What we learned.** The pilot proactively shipped `GroundingError::{Ambiguous, NoInhabitant}` plus structural tests (`pilot_primitives_have_unique_algebra_carrier_keys`, `missing_inhabitant_fails_closed`). The original pilot brief allowed deferring fail-closed discipline to Engine; the worker chose to lock it at pilot scope per `feedback_fail_closed_discipline.md`.
+
+**Source.** Pilot crate `src/v3/grounding_pilot/src/lib.rs`, fail-closed shape per [PR #765](https://github.com/gunb-ai/gunbc/pull/765).
+
+**Forward routing.** Engine doesn't need to *introduce* fail-closed selection — only generalize it (minimum-satisfier selection, structured diagnostics naming candidates). Pilot's bare-vector `Ambiguous { candidates }` is the floor; Engine produces a real diagnostic per the proposal's L4 surface. **This is a contract, not a suggestion** — Engine that drops fail-closed shape regresses against pilot.
+
+**Forward routing (T-Ground-Tests).** L4 witness-based certification can rely on the contract being load-bearing in the engine, not just decorative. Tests can assert against `Ambiguous` / `NoInhabitant` outcomes as first-class behaviors.
+
+### Lesson 4 — SG-0 ratchet drives Engine location decision
+
+**What we learned.** The pilot's manager-brief candidate location (`src/v3/compiler/src/pilot/grounding_pilot.rs`) would have ratchet-bumped the SG-0 hand-Rust ratchet on `src/v3/compiler/`. Worker restructured to a sibling crate (`src/v3/grounding_pilot/`) — strictly better than the manager-brief default because workspace-member removal is a cleaner "deletable as a unit" than module deletion.
+
+**Source.** [PR #765 PR body — "File-location decisions"](https://github.com/gunb-ai/gunbc/pull/765); manager endorsement in [LGTM comment 4317308089](https://github.com/gunb-ai/gunbc/pull/765#issuecomment-4317308089).
+
+**Forward routing.** If Engine remains hand-Rust temporarily (sharpened (b.i) per the substrate-escalation), it must inherit the same SG-0 constraint — sibling-crate or `.dag`-defined, never under `src/v3/compiler/`. The Engine-Phase-1 brief codified this in its Phase 0 audit options ((c) `src/v3/compiler/` is REJECTED on SG-0 grounds).
+
+**Forward routing (T-Ground-Dissolve).** Dissolve scope already expanded to delete `src/v3/grounding_pilot/`. If Engine ships in a sibling crate, Dissolve scope expands further to delete that crate too. Both deletions are workspace-member removals (clean).
+
+### Lesson 5 — State-space discipline: precedent shape for full-reference
+
+**What we learned.** The original `RustPrimitive` declaration carried `overflow: IntegerOverflow?` with a doc-comment convention ("none for non-integer primitives"). Codex P2 review caught the gap: the type admitted illegal state combinations (`bool: Some(TwoComplementWrap)`, `i64: None`). Manager called for a structural fix per `feedback_state_space_vs_behavioral_invariants` and `feedback_no_validation_passes`. Worker partitioned `RustPrimitive` into `IntegerPrimitive | NonIntegerPrimitive` — overflow lives only on the integer variant; structurally absent from non-integer.
+
+**Source.** Codex P2 finding + manager adjudication in [comment 4317414841](https://github.com/gunb-ai/gunbc/pull/765#issuecomment-4317414841); structural-fix commit on the pilot branch.
+
+**Forward routing.** `RustPrimitive`'s sum-type partition is the **precedent shape** that `PythonPrimitive` / `GoPrimitive` inherit. T-Ground-Python / -Go briefs must require state-space discipline at the type-shape level (not via doc-comment convention or `Option`-with-validation). Specifically:
+
+- Identify per-target the analog axes where overflow / Copy-trait / mutability / GIL-affinity / etc. only apply to a subset of primitives.
+- Partition the per-target `Primitive` type structurally so subset-only fields live only on the variants where they're meaningful.
+
+**Forward routing (Engine).** Variant-aware walker handling is a contract: `find_inhabitant` and equivalents must dispatch on `IntegerPrimitive | NonIntegerPrimitive` to extract the variant-typed `algebra` field. The Engine-Phase-1 brief codified this via the state-space-discipline test requirement.
+
+**Forward routing (T-Ground-Dissolve).** Widening `RustPrimitive` back to a flat record is locked out of scope per the codex P2 adjudication. Dissolve cannot simplify the partition away.
+
+---
+
+## What this receipt does NOT contain
+
+- **Worker-level implementation details.** The pilot's engine code, test names, and per-line decisions live in [PR #765](https://github.com/gunb-ai/gunbc/pull/765) and `src/v3/grounding_pilot/src/lib.rs`. This receipt is lessons, not history.
+- **Brief amendments.** Lessons that should reshape future briefs are flagged; the actual amendments happen in the relevant brief PRs.
+- **Director-routed substrate decisions.** The mirroring lesson's substrate ask is documented in [`t-ground-engine-substrate-escalation.md`](t-ground-engine-substrate-escalation.md), not here.
+
+---
+
+## Cross-program implications
+
+- **Pure Bootstrap to Zero program.** The extdeps-loader gap (Lesson 2 forward routing) overlaps directly with PB-1 / PB-Bootstrap-Process scope (`bootstrap.rs` data-driven loader). See substrate-escalation doc for concrete coordination ask.
+- **R1 Substrate Manager (archived on R1 close).** The pilot's lessons about state-space discipline, fail-closed contract, and structural over conventional are general-purpose and should inform DB-11 + cardinality-substrate design decisions if those sub-lanes haven't yet finalized their type shapes. The lessons are framework-level, not Grounding-specific.
+- **R2 Grounding Manager working state.** Lane checklist updated in `grounding-manager.md`. Pilot lane ✅. Engine-Phase-1 audit complete + parked pending loader-close PR (Director routed Route 1; substrate ask is in flight as ad-hoc Director dispatch).
+
+---
+
+## Lineage
+
+- Parent program: ROADMAP.md §"Post-R1 Program — Grounding Completeness" (current); §"Release R2 Program" → T-Ground (post-promotion).
+- Parent thesis claim: THESIS.md Tier 1 → "Grounding completeness."
+- Parent architectural design: [`docs/single-emitter-design.md`](../single-emitter-design.md).
+- Parent worked-examples doc: [`docs/thesis/target-grounding-proposal.md`](../thesis/target-grounding-proposal.md).
+- Sibling artifacts: [`grounding-manager.md`](grounding-manager.md), [`t-ground-engine-phase-1.md`](t-ground-engine-phase-1.md), [`t-ground-engine-substrate-audit.md`](t-ground-engine-substrate-audit.md), [`t-ground-engine-substrate-escalation.md`](t-ground-engine-substrate-escalation.md).