Module interp 

{name}-style template interpolation against a Polydat Kernel.

Surface #5 home (per polydat/docs/design/comprehension_cutover_contact_surfaces.md). Previously lived in polydat::iteration::comprehension::eval; relocated to the kernel module because the operation is general GK-kernel facility, not a comprehension concern. The comprehension runtime uses it; synthesisers use it; the executor uses it; but it doesn’t depend on comprehension AST shape.

Functions

• interpolate_via_kernel — looks up {name} placeholders against the kernel’s chain-aware bindings via PolydatKernel::lookup.
• interpolate_with_lookup — the generic engine; the lookup closure decides where each leaf’s value comes from. Used by callers that compose their own lookup over the kernel plus workload params plus synthesis-time probes.
• collect_string_interp_refs — extracts the placeholder names from a text without doing substitution.

Semantics

Iterative leaf-placeholder substitution with escape handling and a round cap:

• Leaf: {name} whose body contains no further {. The dynamic form {a_{b}_c} is resolved by first substituting {b}, then re-scanning for the resulting {a_<b-value>_c} as a leaf.
• Escape: \{ and \} pass through as literal { / } and are removed from the final string.
• Round cap: if substitution doesn’t stabilize in ROUND_HARD iterations, returns Err (the input had cyclic placeholders).
• Unresolved name: any {name} that survives the substitution rounds errors with a diagnostic naming the missing binding.

Structs

Layered

Bindings in front of another lookup: a tuple’s elements over the scope they were drawn in.

Traits

Lookup

Name resolution for comprehension sources and predicates: what a {name} placeholder or a bare identifier reads. The interpreter kernel is one; a Layered view puts a tuple’s bindings in front of another, so opening a traversal needs no kernel of the engine that opens it (engine parity, step 8).

Functions

collect_string_interp_refs

Extract every leaf {name} placeholder mentioned inside string-literal contexts in src into refs.

interpolate_via_kernel

Interpolate {name} placeholders against kernel.

interpolate_with_lookup

Iterative leaf-placeholder substitution with escape handling, round cap, and final unresolved-name check. The lookup closure decides where each leaf’s value comes from.