diff --git a/src/v4/std/coercion.dag b/src/v4/std/coercion.dag
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+++ b/src/v4/std/coercion.dag
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+// src/v4/std/coercion.dag
+// Scope: exact coercion-fold substrate boundary over canonical groundings.
+// Owns: CoercionCandidate, CoercionCandidateSet, CoercionFoldPolicy, TargetSelectionPolicy, CoercionMismatchKind, CoercionDiagnostic, AcceptedLoss, CoercionQuality, CoercionWitness, CoercionResult, coercion_quality_compose, candidates_for_algebra, coercion_fold, verify_coercion_witness.
+// Consumes: std constraints, std collection, std diagnostic, std node.
+// Status: scaffold — TASKS T-9/T-10; exact-only coercion fold, no rewrites.
+// Anchor: docs/design-v4-compiler-homomorphism.md P7.
+
+
+module v4.std.coercion
+
+
+import v4.std.collection { List }
+import v4.std.constraints { CanonicalGrounding }
+import v4.std.diagnostic {
+  Diagnostic,
+  ExternalContractUnknown,
+  Locus,
+  Outcome,
+  PortLocus,
+  Rejected,
+  Unavailable
+}
+import v4.std.node { Node, Symbol }
+
+
+type CoercionCandidate {
+  target: CanonicalGrounding
+}
+
+
+type CoercionCandidateSet {
+  target_model: Node
+  algebra_instance: Node
+  candidates: List<CoercionCandidate>
+}
+
+
+type TargetSelectionPolicy
+
+
+type CoercionFoldPolicy {
+  target_selection: TargetSelectionPolicy
+}
+
+
+// 🟢 coproduct dissolution — CP-3229-GREEN-TERMINAL.
+type CoercionMismatchKind
+  = NoTargetCandidate
+  | AmbiguousTargetCandidate
+  | StructuralMismatch
+
+
+type CoercionDiagnostic {
+  kind: CoercionMismatchKind
+  at: Locus
+}
+
+
+type AcceptedLoss {
+  declaration: Node
+}
+
+
+// 🟢 coproduct dissolution — CP-3229-GREEN-TERMINAL.
+type CoercionQuality
+  = Identity
+  | Exact
+  | Lossy { accepted_loss: AcceptedLoss }
+
+
+type CoercionWitness {
+  source: CanonicalGrounding
+  target: CanonicalGrounding
+}
+
+
+type CoercionResult {
+  witness: CoercionWitness
+  target: Node
+  quality: CoercionQuality
+}
+
+
+data coercion_fold_stage_locus_port: Symbol = coercion_fold_stage_locus_port
+data no_target_candidate: Symbol = no_target_candidate
+data ambiguous_target_candidate: Symbol = ambiguous_target_candidate
+data structural_mismatch: Symbol = structural_mismatch
+data coercion_fold_not_realized: Symbol = coercion_fold_not_realized
+data coercion_candidates_not_realized: Symbol = coercion_candidates_not_realized
+data coercion_witness_verification_not_realized: Symbol = coercion_witness_verification_not_realized
+
+
+fn coercion_mismatch_reason(kind: CoercionMismatchKind) -> Symbol {
+  match kind {
+    NoTargetCandidate => no_target_candidate
+    AmbiguousTargetCandidate => ambiguous_target_candidate
+    StructuralMismatch => structural_mismatch
+  }
+}
+
+
+fn coercion_diagnostic(d: CoercionDiagnostic) -> Diagnostic {
+  Diagnostic {
+    reason: coercion_mismatch_reason(kind: d.kind),
+    at: d.at,
+    correction: Unavailable { reason: ExternalContractUnknown }
+  }
+}
+
+
+fn coercion_quality_compose(left: CoercionQuality, right: CoercionQuality) -> CoercionQuality {
+  match left {
+    Lossy { accepted_loss } => Lossy { accepted_loss: accepted_loss }
+    Identity => right
+    Exact => match right {
+      Lossy { accepted_loss } => Lossy { accepted_loss: accepted_loss }
+      Identity => Exact
+      Exact => Exact
+    }
+  }
+}
+
+
+fn candidates_for_algebra(target_model: Node, algebra_instance: Node) -> Outcome<CoercionCandidateSet> {
+  Rejected {
+    diagnostic: Diagnostic {
+      reason: coercion_candidates_not_realized,
+      at: PortLocus { port: coercion_fold_stage_locus_port },
+      correction: Unavailable { reason: ExternalContractUnknown }
+    }
+  }
+}
+
+
+fn coercion_fold(
+  source: CanonicalGrounding,
+  candidates: CoercionCandidateSet,
+  policy: CoercionFoldPolicy,
+) -> Outcome<CoercionResult> {
+  Rejected {
+    diagnostic: Diagnostic {
+      reason: coercion_fold_not_realized,
+      at: PortLocus { port: coercion_fold_stage_locus_port },
+      correction: Unavailable { reason: ExternalContractUnknown }
+    }
+  }
+}
+
+
+fn verify_coercion_witness(witness: CoercionWitness) -> Outcome<CoercionWitness> {
+  Rejected {
+    diagnostic: Diagnostic {
+      reason: coercion_witness_verification_not_realized,
+      at: PortLocus { port: coercion_fold_stage_locus_port },
+      correction: Unavailable { reason: ExternalContractUnknown }
+    }
+  }
+}
diff --git a/src/v4/std/constraints.dag b/src/v4/std/constraints.dag
new file mode 100644
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--- /dev/null
+++ b/src/v4/std/constraints.dag
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+// src/v4/std/constraints.dag
+// Scope: constraint-solving substrate boundary for canonical source grounding.
+// Owns: ConstraintKind, Constraint, ConstraintSource, ConstraintGraph, ConstraintSolvePolicy, CanonicalGrounding, CanonicalGroundingWitness, ConstraintSolveResult, AmbiguousGroundingDiagnostic, UnsatisfiedConstraintDiagnostic, solve_constraints.
+// Consumes: std collection, std diagnostic, std node.
+// Status: scaffold — TASKS T-9; exact canonical-grounding boundary only.
+// Anchor: docs/design-v4-compiler-homomorphism.md P5.
+
+
+module v4.std.constraints
+
+
+import v4.std.collection { List }
+import v4.std.diagnostic {
+  Diagnostic,
+  ExternalContractUnknown,
+  Locus,
+  Outcome,
+  PortLocus,
+  Rejected,
+  Unavailable
+}
+import v4.std.node { Hash, Node, Symbol }
+
+
+// 🟡 coproduct dissolution — feature:t9-solve-constraints-consumer.
+type ConstraintKind
+  = TypeShapeConstraint
+  | InhabitanceConstraint
+  | EqualityConstraint
+  | DependencyConstraint
+
+
+// 🟢 coproduct dissolution — CP-3229-GREEN-TERMINAL.
+type ConstraintSource
+  = SourceNode { node: Node }
+  | SourceEdge { from: Node, to: Node }
+  | SourceStage { stage: Symbol }
+
+
+type Constraint {
+  kind: ConstraintKind
+  source: ConstraintSource
+  left: Node
+  right: Node
+}
+
+
+type ConstraintGraph {
+  root: Node
+  constraints: List<Constraint>
+}
+
+
+type ConstraintSolvePolicy
+
+
+type CanonicalGroundingWitness {
+  source_graph: ConstraintGraph
+  canonical_hash: Hash
+}
+
+
+type CanonicalGrounding {
+  root: Node
+  witness: CanonicalGroundingWitness
+}
+
+
+type ConstraintSolveResult = Outcome<CanonicalGrounding>
+
+
+type AmbiguousGroundingDiagnostic {
+  graph: ConstraintGraph
+  at: Locus
+}
+
+
+type UnsatisfiedConstraintDiagnostic {
+  constraint: Constraint
+  at: Locus
+}
+
+
+data constraint_solve_stage_locus_port: Symbol = constraint_solve_stage_locus_port
+data ambiguous_grounding: Symbol = ambiguous_grounding
+data unsatisfied_constraint: Symbol = unsatisfied_constraint
+data constraint_solver_not_realized: Symbol = constraint_solver_not_realized
+
+
+fn ambiguous_grounding_diagnostic(d: AmbiguousGroundingDiagnostic) -> Diagnostic {
+  Diagnostic {
+    reason: ambiguous_grounding,
+    at: d.at,
+    correction: Unavailable { reason: ExternalContractUnknown }
+  }
+}
+
+
+fn unsatisfied_constraint_diagnostic(d: UnsatisfiedConstraintDiagnostic) -> Diagnostic {
+  Diagnostic {
+    reason: unsatisfied_constraint,
+    at: d.at,
+    correction: Unavailable { reason: ExternalContractUnknown }
+  }
+}
+
+
+fn constraint_solver_not_realized_diagnostic(at: Locus) -> Diagnostic {
+  Diagnostic {
+    reason: constraint_solver_not_realized,
+    at: at,
+    correction: Unavailable { reason: ExternalContractUnknown }
+  }
+}
+
+
+fn solve_constraints(
+  graph: ConstraintGraph,
+  policy: ConstraintSolvePolicy,
+) -> ConstraintSolveResult {
+  Rejected {
+    diagnostic: constraint_solver_not_realized_diagnostic(
+      at: PortLocus { port: constraint_solve_stage_locus_port }
+    )
+  }
+}