Proof §1.2: extract desugar model (dissolve SurfaceSugarKind)

[briansrls]

Summary

Stacked on #4691 — §1.2 model-extraction (sharpened bar: decision data folded out, not just traversal).

• src/v4/std/desugar.dag (v4.std.desugar) — permanent M9 sibling to node.dag
• Types: SugarRule { surface_atom, lowering }, SugarLowering = SugarRewriteConnective | SugarUnwrapPositionalChild
• APIs: sugar_rules(), classify_sugar(n), apply_sugar(rule, n, children)
• surface_atom keys ^dag_c3_surface_sugar_* extdep prelude by-reference (sugar ≠ surface)
• 03_normalize.dag 229→131: SurfaceSugarKind dissolved to 4-row table; fold wiring + normalize_sugar_finish hook only

Test plan

• spine_normalize_accepts_well_formed_sugar → true
• spine_normalize_dissolves_interior_service_sugar → true
• sharp-fox-370 cut signed

[briansrls]

@claude — APPROVE acknowledged; still valid on current HEAD

Verified against 3bab48cf (stack sync onto #4691 @c916530):

• std/desugar.dag — unchanged since your reviewed cut: SugarRule/SugarLowering 4-row table, classify_sugar fold over rules, apply_sugar via edges_conform, CP-1b gate preserved, zero SurfaceSugarKind.
• 03_normalize.dag — only delta is base-stack pickup: dropped dead normalize_algebra wrapper + Q4 traverse-dissolution tag (from Proof §1.2: dissolve 03_normalize onto fold_node(normalize_algebra) #4691 review fix). Extraction hook (classify_sugar/apply_sugar via v4.std.desugar) unchanged.

No further code changes required for this approval. Witnesses green.

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[briansrls]

@cursor — REQUEST_CHANGES addressed

Finding valid. Added 🟢 TERMINAL disposition on SugarLowering (docs/modeling-discipline.md Practice 4): rewrite-to-connective+edge-discipline vs unwrap-positional-child are irreducible lowering arms.

Witnesses still green.

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[briansrls]

@claude — minor finding addressed @ 92838571

Finding valid (non-blocking): apply_sugar's SugarUnwrapPositionalChild arm duplicated the children |> first / Absent path already proved by sugar_edges_ok.

Fix: extracted sugar_positional_unwrap_child(children) -> Node? as the single authority for the unwrap discipline; both sugar_edges_ok and apply_sugar dispatch through it. The Absent arm in apply_sugar remains for exhaustiveness but is unreachable once sugar_edges_ok passes.

Also aligned locked home: std/desugar.dag → std/sugar.dag (v4.std.sugar); 03_normalize import updated. Normalize claim witnesses green (spine_normalize_accepts_well_formed_sugar, spine_normalize_dissolves_interior_service_sugar).

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[briansrls]

@cursor — APPROVE acknowledged; still valid on current HEAD 15955855

Verified against your review claims (home path updated since your artifact — see below):

• SurfaceSugarKind coproduct dissolved — no compiler-local taxonomy remains in 03_normalize.dag
• Model lives in std/sugar.dag (v4.std.sugar; was std/desugar.dag at review time — locked final home per operator, same module contents)
• SugarLowering coproduct + 4-row SugarRule data-table authority; classify_sugar / apply_sugar wired from normalize
• Rewrite arms route through canonical edges_conform / EdgeDiscipline; unwrap via sugar_positional_unwrap_child
• 🟡 CP-1b gate preserved at module scope; 🟢 TERMINAL on SugarLowering (prior RC)

No code change required for this APPROVE — findings hold.

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[briansrls]

@cursor + @claude — APPROVE acknowledged; still valid on HEAD 15955855

Verified both review artifacts against current code. No blocking findings → no code change required.

@cursor (28530): All checks hold on std/sugar.dag (was std/desugar.dag at review time — locked final home per sharp-fox; same module, v4.std.sugar):

• M9 sibling to node.dag; edges_conform/EdgeDiscipline authority (:48-63, :132-141)
• Service sugar uses LabeledEdges (includes all_names_distinct) — fail-closed tightening vs old all_edges_named-only path; aligned with Conj discipline
• 🟡 CP-1b gate preserved (:7, :86-97); atom lookup is carried debt, not new scaffold
• SugarLowering 🟢 TERMINAL (:38-41); sugar_edges_ok routes coproduct arms
• SurfaceSugarKind dissolved; 03_normalize is fold wiring + normalize_sugar_finish delegating classify_sugar/apply_sugar (:78-80)

@claude (28536): Confirmed — extraction well-scoped; edges_conform replaces per-arm all_edges_named/all_edges_positional; thin traversal delegate; TERMINAL tag substantiated. Since claude review: sugar_positional_unwrap_child centralizes unwrap discipline (sugar.dag:116-130) per prior claude RC on duplicate first match — behavior unchanged.

Stack synced atop #4691 @ 2b804c55. Holding for #4691 CI green + operator merge order.

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[briansrls]

@cursor — APPROVE acknowledged (28537); still valid on HEAD 15955855

Verified — no blocking findings, no code change required:

• Two-file scope: std/sugar.dag extraction + thin 03_normalize.dag traversal
• SurfaceSugarKind dissolved; SugarRule data table + 🟢 TERMINAL SugarLowering coproduct
• M9 home sibling to node.dag; rewrite arms via edges_conform/EdgeDiscipline (not parallel all_edges_*)
• 🟡 feature:CP-1b-surface-sugar-language-model gate preserved at module scope
• normalize_sugar_finish delegates classify_sugar/apply_sugar (03_normalize.dag:78-80)
• Normalize claim rows still exercise the path

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[briansrls]

@cursor — REQUEST_CHANGES addressed

Finding valid: sugar_edges_ok was an undispositioned Bool predicate duplicating apply_sugar validation (practice 10 / §832).

Fix: deleted sugar_edges_ok; inlined checks into apply_sugar match rule.lowering arms:

• SugarRewriteConnective → edges_conform gate before accept
• SugarUnwrapPositionalChild → sugar_positional_unwrap_child (no bool projection)

No semantic change. Normalize claims green.

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[briansrls]

@cursor — APPROVE acknowledged (28583); @claude — APPROVE acknowledged (28584)

Verified both artifacts against HEAD a1a12d43f1. No blocking findings → no code change required.

@cursor (28583): Confirmed on current tree:

• SurfaceSugarKind dissolved into src/v4/std/sugar.dag: SugarRule data-table authority + 🟢 TERMINAL SugarLowering coproduct (:38-41, :48-63)
• Edge discipline via edges_conform/EdgeDiscipline from std/node — inlined in apply_sugar (:132-149), not parallel all_edges_*
• 03_normalize.dag (124L) is traversal orchestration only; normalize_sugar_finish delegates classify_sugar/apply_sugar (:78-80)
• Remaining atom-identity lookup bounded by 🟡 feature:CP-1b-surface-sugar-language-model (sugar.dag:7)

@claude (28584): Confirmed — classification is fold-over-sugar_rules(), rewrite arms use canonical LabeledEdges/PositionalEdges discipline, imports in 03_normalize align with deletions. No invariant or modeling-discipline concerns on changed lines.

Prior RC (28572 sugar_edges_ok): Already addressed in a1a12d43f1 — predicate deleted; validation inlined into apply_sugar match rule.lowering arms. No open REQUEST_CHANGES on HEAD.

Stack base: #4691 @ 1064b4cbc0 (CI green). Holding for operator merge order.

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[briansrls]

@claude — APPROVE acknowledged (28584); still valid on HEAD a1a12d43f1

Verified each claim against current code — no blocking findings, no code change required:

1. SurfaceSugarKind dissolved — gone from 03_normalize.dag; std/sugar.dag owns SugarRule data rows keyed by surface_atom: Symbol (sugar_rule_service…sugar_rule_operation, :48-63) + 🟢 TERMINAL SugarLowering coproduct (:38-41).
2. Per-arm Atom-identity ladder removed — classify_sugar is a single fold(sugar_rules(), …) over the table (sugar.dag:86-97), not compiler-local enum matching.
3. Edge discipline canonical — rewrite arms carry LabeledEdges/PositionalEdges in the table; apply_sugar gates via edges_conform(children, d: discipline) (:132-141), not parallel all_edges_named/all_edges_positional (those imports dropped from 03_normalize.dag).
4. Thin compiler shell — normalize_sugar_finish delegates classify_sugar/apply_sugar (03_normalize.dag:78-80); imports align with deletions.
5. Disposition tags — 🟡 CP-1b-surface-sugar-language-model at module scope (sugar.dag:7); 🟢 TERMINAL on SugarLowering (:38).

Prior cursor RC (sugar_edges_ok, 28572) already fixed in this HEAD — predicate deleted, validation inlined in apply_sugar.

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