design: §3 emit breadth DEEP lane (PRE-ROUND-TRIP census, ladder, Rust descriptor)

docs/planning/v4-emit-breadth-deep-lane-design-2026-06-12.md

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+# §3 Emit Breadth — DEEP Lane Design (dep-graph-2026-06-12 §3)
+
+> **Status: PRE-ROUND-TRIP DESIGN ONLY** — no compiler-stage `.dag` edits from this artifact.
+> **Work item:** `node://adhoc-f64ad6df-d11` · **Session:** `clever-moth-532` (Mgr-§3 composite).
+> **Planning authority:** `gunb-ai/ctrl` `gunbc-planning/dependency-graph-2026-06-11.md` §3 +
+> `dependency-graph-2026-06-12.md` frontier update.
+> **Operator fork (2026-06-12, ctrl#1563 via snappy-crab):** **§3-DEEP / §4-THIN** — standing
+> decision, no fresh operator call. §3 inherits deepest capacity the day a Branch body
+> round-trips; §4 is ONE thin bounded lane (`royal-ferret`, `program.dag` PR #4744).
+>
+> **Implementation GO:** sharp-fox-370 **owns announcing GO** when fan-in **(iii) round-trip**
+> greens (downstream of fan-in **(ii) emit**, in flight: `valiant-swift-466` PR #4741).
+> Until GO: **NO** compiler-stage `.dag` edits, **NO** emit-surface code.
+>
+> **Operator pivot (2026-06-12):** ctrl tooling goes 100% TS and will depend on gunbc TS
+> emission at build time — §3 is the **program spine**, not breadth-only work.
+
+## 1. North star — one row per form, rows not arms
+
+**§3 principle:** emit breadth = **N algebra rows in `target_model`**, not N×M hand-arms in
+`06_translate` / `06_value_expression`. `05_emit` stays frozen (`serialize ∘ translate`).
+
+**Standing invalidation (keystone dissolve):** any source form needing **>1**
+`TargetValueExpressionKind` arm **or** multi-site `06_translate` edits **falsifies** the
+keystone — **STOP and escalate to snappy-crab-849**; that is a finding, not an obstacle to
+work around.
+
+**Anti-cement precedent (#4623):** TypeScript went **through the descriptor** (`TargetValueExpressionProjection` + operator catalog on `TargetModel`); the enumerated hand token list (`ts_mvp1_concrete_tokens`) is marked dissolve-on, not re-expanded. A second target must **never** re-introduce per-language hand-lists in compiler code or parallel token tables.
+
+**P2 audit rule:** every PR touching compiler stages must sweep **all** stage `.dag` files —
+including `emit_host.dag` (past audit missed it by only checking `06_translate`). Emit-surface
+diffs in load-bearing stages route through snappy-crab-849 for signing authority.
+
+### 1.1 Day-1 tripwires (ctrl#1563 fork ruling — bake now)
+
+| Tripwire | Falsifier | Action |
+|----------|-----------|--------|
+| **§1 regression** | Second-target emit **edits** `06_translate` fold logic instead of **adding** `target_model` rows consumed by existing folds | **STOP** — §1 regressed; escalate sharp-fox-370 |
+| **Anti-cement (#4623)** | `run_emit_host` hand-list deletion before TS **round-trips through the descriptor** | **HOLD** — hand-list dies only after descriptor round-trip proof |
+| **One row per form** | >1 `TargetValueExpressionKind` or multi-site translate matcher | **STOP** — escalate snappy-crab-849 |
+
+## 2. Emit-coverage census — BY EXECUTION
+
+Witnesses run 2026-06-12 on `target/release/gunbc run --source-root src/v4 --entry … --function … --claim-run` at main tip (`b7411556ef`). **Do not infer green from code.**
+
+### 2.1 Today's proof shape vs today's colors
+
+**Keystone proof shape (operator brief):** add **signature + body** → TypeScript **end-to-end**
+(producer-rooted `Arrow.body` → `emit()` → authority source string, discriminating mutates).
+
+| Witness | Entry | claim-run | Tier |
+|---------|-------|-----------|------|
+| `mvp1_ts_emit_add_fn_accepts_holds` | `mvp1_typescript_add_translate.dag` | **true** | signature-only (hand-built `InferredTree` fixture root) |
+| `comprep_ts_bodied_emit_add_fn_accepts_holds` | `comprep_add_body_emit_typescript.dag` | **false** | signature **+ body** (producer-rooted) |
+| `comprep_ts_bodied_emit_operand_swap_discriminates` | same | **false** | body perturbation red |
+| `comprep_ts_bodied_emit_catalog_minus_discriminates` | same | **false** | catalog perturbation red |
+| `comprep_ts_bodied_emit_missing_catalog_rejects` | same | **true** | fail-closed (missing catalog → Rejected) |
+| `comprep_eval_by_execution_keystone_holds` | `comprep_eval_by_execution.dag` | **false** | add body **eval** — stale witness vs #4737/#4738 semantics (culprit #4737) |
+| `comprep_branch_eval_by_execution_keystone_holds` | `comprep_branch_eval_by_execution.dag` | **true** | Branch body **eval** |
+
+**Honest summary:** **signature-tier** TS emit is green by execution; **body-tier** add eval and
+body-tier TS emit are **red-baseline** (not green) in this environment. Fail-closed
+operator-catalog refusal is green. Branch eval is green; Branch emit and round-trip tracked on
+§2 lane (#4741 sign stage).
+
+**Triage (snappy-crab, 2026-06-12 — bisect final):** `comprep_eval_by_execution_keystone_holds`
+**TRUE** at `af4530cc0e` (#4735), **FALSE** at `9e26842d53` (**culprit #4737**). Not
+known-false ledger. Likely disposition: stale witness clauses asserting #4737 interim
+channel-suppression semantics that #4738 demand-driven dispatch superseded (sharp-fox drilling
+exact clause by execution); fix = witness update to ruled semantics unless a non-control
+clause flipped. **Meta-finding:** manual claim corpus has no CI gate — wave PR merged with its
+own witness red; gate design → ctrl graph amendment (not inline here).
+`comprep_ts_bodied_emit_*` classification **unaffected** — red before the wave.
+
+### 2.2 Which source forms emit today (execution truth)
+
+| Source form | Parses | Produces body | Eval | Emit TS | Notes |
+|-------------|--------|---------------|------|---------|-------|
+| `fn add(…) -> … { x + y }` signature only | ✅ | fixture only | — | ✅ fixture tree | `mvp1_ts_emit_*` |
+| `fn add(…) { x + y }` body (producer) | ✅ | ✅ `produce_mvp1_add_arrow_with_body` | ❌ | ❌ | #4623 consumer red |
+| `fn pick(b) { if b then … else … }` | ✅ | ✅ source-bridged | ✅ | ❌ | fan-in (ii) pending |
+| `let` / `match` / general call | grammar exists | ❌ | ❌ | ❌ | §2+ breadth |
+| Rust / Python / Go MVP signature | fixtures | ❌ body | — | grammar-inverse signature only | no value projection row |
+
+### 2.3 What does NOT emit (named)
+
+- Any form without a landed `TargetValueExpressionKind` + per-target projection row.
+- Branch `if`-then-else body tokens (no `TargetValueExprConditional` kind yet).
+- Callable / method apply bodies (`TargetValueExprCallableApply` absent).
+- `Bind` / `Loop` bodies (kinds absent; §2 producers open).
+- Host execute of emitted TS (`run_emit_host` — only TS routes through `run_host_process` descriptor; rust/python/go substrate rows fail-closed; eval intercept in `emit_host_eval.rs`).
+
+## 3. Breadth ladder — ordered source forms (post-Branch)
+
+Each rung = **exactly one** `TargetValueExpressionKind` + **one** projection fold arm + **one**
+serialize arm. Nested/block variants (B2/B3) use **recursive projection on the same kind**, not
+new kinds (`design-comprep-m0-branch-mapping.md` §12.1 tripwire).
+
+### 3.0 Early deliverable — stable emit CLI façade (ctrl build contract)
+
+**Problem:** v4 TS emit is invocable only in-language today (`gunbc run --source-root …
+--entry … --function …` on the v2 interpreter). ctrl's TS build needs a **stable external
+contract** that does not bind to internal `.dag` fn names.
+
+**Contract (target shape):**
+
+```text
+gunbc emit --target <lang> --source-root <dir> --entry <program.dag> [--output <path>]
+```
+
+- **Thin façade only** — wraps the existing v4 `emit(tree, target)` path (parse → infer →
+  `emit`); **no new emission logic**, no duplicate translate/serialize.
+- **Useful from L0 onward** — slot as first implementation worker after GO (parallel to L0
+  body-emit greens); ctrl can consume as soon as signature+bodied paths emit for TS.
+- **Layer separation (do not conflate):**
+  - `gunbc compile` — **v2 bootstrap pipeline** (`compile_sources` /
+    `emit_resolved_for_target` in `main.rs`); emits v2 stage0 / multi-file bootstrap output.
+  - `gunbc run` — v2 interpreter + scoped `--claim-run` witnesses.
+  - `gunbc emit` — **v4 translate-path emission** to target source text/files; new surface.
+- **Façade home (design ruling):** stage0 CLI — new `Emit` subcommand alongside `Compile` /
+  `Run` (`src/v2/stage0/src/main.rs` generated shell + hand-maintained handler module, same
+  pattern as `cli_run.rs` for `Run`). Handler calls into v4 emit authority; does not grow
+  compiler-stage `.dag` logic.
+
+**Acceptance:** emit TS for `mvp1` / producer-rooted add program writes authority source text
+to `--output`; discriminating receipt = same strings as existing `claim-run` emit witnesses.
+
+### 3.1 North-star fixture — `ctrl` `plans/models/plan_checks.dag`
+
+**Role:** breadth **driver** once operator delivers form-census — **not** the first acceptance
+fixture (too many forms at once). First acceptance stays **per-rung witnesses** as designed.
+
+| Aspect | Rule |
+|--------|------|
+| **Prioritization** | Ladder rung **order** follows `plan_checks` **blocking forms** (form census pending from operator) |
+| **Acceptance growth** | Largest `plan_checks` **subset** emittable with landed forms at each milestone |
+| **Ladder structure** | L0→L1→BindLet→Loop→CallableApply **unchanged**; records/lists/fold rungs likely **pulled earlier** than current draft once census lands (`plan_checks` is plan/record-heavy) |
+| **Status** | 🟡 pending form-census from operator; placeholder until census lands |
+
+### 3.2 Ordered source forms (default rung table — reprioritize when census lands)
+
+| Order | Source form (`dag.dag`) | One algebra row | Producer gate | Eval fan-in | Emit fan-in | Round-trip |
+|-------|-------------------------|---------------|---------------|-------------|-------------|------------|
+| L0 | infix primitive (`+` add keystone) | `TargetValueExprPrimitiveApply` | ✅ wave-1 | ❌ stale witness (#4737 culprit; #4738 semantics) | ❌ red pre-wave (emit) | witness fix or ctrl gate |
+| L1 | `dag_production_if_then_form` | `TargetValueExprConditional` | ✅ M0-B1 | ✅ green | sharp-fox (ii) | sharp-fox (iii) → **§3 GO** |
+| L2 | cond = param ref (B1a) | same `Conditional` | B1a | follow-on | same row | — |
+| L3 | `dag_production_if_block_form` | same `Conditional` + stmt scaffold | Bind producer | §2 | same row | — |
+| L4 | nested else `if` (B3) | recursive `Conditional` | M0-B1 + Bind | recursive eval | recursive serialize | — |
+| L5 | `dag_production_let_expr` | `TargetValueExprBindLet` | §2 Bind | §2 | one row | — |
+| L6 | bounded `loop` | `TargetValueExprLoop` | §2 Loop | §2 | one row | — |
+| L7 | callee `Transform` (non-primitive) | `TargetValueExprCallableApply` | callee path | §2 | one row | — |
+| L8 | record / list literals | leaf kinds or new substrate decision | wave-4 | — | escalate if >1 row | — |
+| L9 | `dag_production_match_expr` | desugar → L1 (M0-B6) **or** escalate Q-B1 | pattern authority | — | **forbidden** second kind without ruling | — |
+
+**Tripwire examples that MUST escalate:**
+
+- Splitting `TargetValueExprMatch` off `Conditional` for Bool match (violates one-row rule).
+- Second `06_translate` matcher parallel to `project_arrow_body_to_value_expression`.
+- Re-adding `ts_mvp1_concrete_tokens`-style enumerated body tokens per target (#4623 regression).
+
+## 4. Rust-second-target plan — through the descriptor
+
+Rust is the **second Shape-A target** after dag home + TS vetting consumer. Plan lands **only**
+as `extdeps/languages/rust.dag` descriptor data + `TestClaim` witnesses — **zero** new
+`run_emit_host_rust` hand-edits, **zero** compiler if-chain arms.
+
+### 4.1 What Rust adds (data only)
+
+| Descriptor | Location | Purpose |
+|------------|----------|---------|
+| `rust_value_expression_projection()` | `rust.dag` | `binding_ref_form`, `primitive_apply_form` (infix-only M0), `callable_apply_form` shell; `conditional_form` with fan-in (ii) |
+| `rust_operator_realizations_catalog_node` | `rust.dag` | `OpAdd` → `InfixToken { ^rust_token_plus }` |
+| `rust_mvp1_value_projection_bundle_node` | `rust.dag` | edge `target_model_edge_value_expression_projection` |
+| `rust_host_transport_mvp1_descriptor()` | `rust.dag` | **HostTransportDescriptor** row (mirror `ts_host_transport_mvp1_descriptor`) — compile/run/stdout codec as data |
+| `rust_mvp1_runtime_row` (T-22) | `rust.dag` on `TargetModel` | promoted typed row replacing authority-text if-chain lookup |
+
+### 4.2 What Rust dissolves (never re-expands)
+
+| Incumbent | Dissolution trigger | Anti-pattern |
+|-----------|---------------------|--------------|
+| `emit_host.dag` `runtime_value_parse` if-chain (`:215-229`) | `TargetModel.runtime_row` generic lookup (#4674) | 4th/5th `else if authority_source_text == …` arm |
+| `emit_host.dag` `run_emit_host` if-chain (`:284-299`) | descriptor fold + `run_host_process` only | per-target `run_emit_host_rust` substrate stub growth |
+| `emit_host_eval.rs` `try_dispatch_emit_host_*` | substrate Callable owns dispatch | name-string intercept per target |
+| `tools/emit_host_runner` near-duplicate bodies | one primitive + descriptor rows | copy-paste spawn/capture per lang |
+| SG-0 `emit_host_bridge.rs` / `emit_host_eval.rs` | D1/D2 in §5 | hand-Rust eval hook |
+| Enumerated body token tables in extdeps | derived projection output | `rust_mvp1_concrete_tokens` parallel |
+
+**T-22 mark (authoritative):** `emit_host.dag:216` and `:289` — *promote typed `runtime_row`
+onto `TargetModel`; replace per-target if-chains + `emit_host_eval.rs` mirror; **forbidden:**
+adding a 5th per-target arm without dissolution.*
+
+Rust second-target work **extends the descriptor fold**, it does not add a fifth hand-list entry.
+
+### 4.3 Sequencing
+
+```text
+sharp-fox: Branch fan-in (ii) emit + (iii) round-trip on dag
+  → Rust descriptor PR (extdeps + claim-run only; P2 sweep includes emit_host.dag)
+    → TS body emit greens (producer path) — same PR or immediate follow-on
+      → Rust value projection attach + body emit claim-run
+        → T-22 runtime_row promotion PR (dissolves if-chains, not extends them)
+          → python/go descriptor clones (no new compiler arms)
+```
+
+## 5. §5 census-drain ordering
+
+**Rule (INVARIANTS / ROADMAP §0):** self-host counter goes down by **migration** — repoint
+consumer onto fold/model, delete hand Rust in the **same PR** — **never** by stuffing Rust into
+templates or cementing per-target logic to satisfy a ratchet.
+
+### 5.1 Emit-breadth-enabled drain (after body emit exists)
+
+| Order | SG-0 / bridge path | Migration replacement | §3 rung that unlocks |
+|-------|-------------------|----------------------|----------------------|
+| D1 | `emit_host_eval.rs` | `TargetModel.runtime_row` + generated eval transport | TS descriptor round-trip green (#4623) + T-22 row |
+| D2 | `emit_host_bridge.rs` | same | D1 |
+| D3 | `r1c_e_emit_gates.rs` + bin | `.dag` claim runner | L1 emit receipts |
+| D4 | `boundary_emit_gates.rs` + bin | T-PB-B claim execution | breadth claims |
+| D5 | `post_emit_verifier.rs` | `run_target_verification` substrate | host descriptor green |
+| D6 | `emit_rust.rs`, `emit/*.rs` | v4 `serialize ∘ translate` per module | convergence ladder B |
+| D7 | `regen_*_emit.rs` | `compiler.dag` emits stage0 | stage C fixed point |
+
+### 5.2 What NOT to drain early
+
+- Do not delete SG-0 emit entries before the **executed** claim-run witness replaces the capability.
+- Do not shrink census by moving logic into `06_translate` string templates (graft detection: file grows).
+- `hand_maintained_src` seed (v2 binary) drains at stage C only — emit breadth accelerates D1–D6, not the seed.
+
+## 6. §4 thin lane (operator decided)
+
+§4 runs thin: landed effect handlers + one §2 body + run loop → first `dag run program.dag`.
+**Falsifier:** one real effect needing bespoke per-effect Rust glue → escalate (breaks #4609 fabric claim). Mgr-§3 does not deepen §4.
+
+## 7. Child dispatch (post-GO only)
+
+| # | When | Owner hint |
+|---|------|------------|
+| W0 | Branch round-trip green | sharp-fox `adhoc-fdd9ccb8-b54`; (ii) emit: valiant-swift-466 #4741 |
+| W_emit | **Emit CLI façade** (`gunbc emit --target ts`) | stage0 handler + v4 emit hook; early, parallel L0 |
+| W1 | Rust descriptor + claims | extdeps worker; P2 sweep all compiler stages |
+| W2 | TS body emit red → green | producer→emit path; no hand token list |
+| W3 | T-22 runtime_row | model PR; dissolves emit_host if-chains |
+| W4 | python/go descriptor clone | after Rust proof |
+
+## 8. Non-goals
+
+- No compiler-stage edits until GO.
+- No parallel-ledger docs; marks stay authoritative.
+- No second `TargetValueExpressionKind` for Branch family.
+- No per-target hand-lists (#4623 regression).
+
+## 9. Escalation
+
+`dashboard-ops escalate` when blocked; `dashboard-message send --to snappy-crab-849` for rulings.
+
+Escalate immediately if:
+
+- Any ladder rung requires >1 kind or multi-site translate.
+- Implementation proposes a 5th `emit_host` per-target arm before #4674.
+- Body emit is ratcheted green without claim-run witness.
+
+## 10. Acceptance (this artifact)
+
+- [x] Emit-coverage census by execution (§2)
+- [x] Breadth ladder with one-row invalidation (§3)
+- [x] Rust-second-target through descriptor + T-22 dissolve plan (§4)
+- [x] §5 census-drain ordering (§5)
+- [x] §3-deep / §4-thin fork recorded (§6)
+- [x] Emit CLI façade early deliverable (§3.0)
+- [x] `plan_checks.dag` north-star fixture slot (§3.1; census pending)
+- [ ] Implementation GO — sharp-fox-370 announces when fan-in (iii) round-trip green