Wiring-liveness wave-2(b): fn-arrow reflection builtin + corpus-wide lens coverage

[briansrls]

Wiring-liveness wave-2(b): fn-arrow reflection + corpus-wide lens coverage

Closes the wave-1 lens's honest boundary — "the corpus has NO fn/arrow reflection ... a corpus-wide scan of real fn params is opaque today" — by landing the gunbc#5364 widen trigger: a fn/arrow corpus-reflection builtin wired into v2.lens.wiring_liveness so a declared fn parameter with no path to its output fails the floor. Builds on wave-1 (#5679); does not fork its kernel.

What lands

• v2.std.fn_index.fn_arrow_decl_facts_live — host SOURCE reflection (sibling of concept_decl_facts_live, but ItemKind::FnItem/FuncItem). Yields one FnArrowDecl{qualified_name, name, output, params} per declared fn: the body projected to a reachability skeleton (parameter references → identity Atom leaves, everything else → neutral Conj containers) plus the declared parameter atoms. Bridge wired in v1_interpreter.rs (STD_FN_INDEX_BRIDGE_FNS / is_v4_std_fn_index_bridge_call), conformance-checked.
• v2.lens.wiring_liveness corpus fold — wiring_dead_wires_over / wiring_liveness_corpus_is_clean. Reuses std.dependency DependencyView/dependency_lens/ready_set (no new dependence type — that re-coining is what sank the duplicate Wiring-liveness lens wave 1: dependence carrier + wired floor witness #5702). A parameter is wired iff reachable from the body output; the per-fn reachable set is computed once via ready_set (linear), not per-parameter saturation (quadratic).
• Floor witness wiring_liveness_corpus_test.dag (auto-enrolled) — with no-host-enumeration controls (locally-authored probe fns must appear in the enumeration, proving the read axis by execution) and a synthetic dead-wire discrimination control.

Soundness (three corrections found by running it over the live corpus)

1. item.params is concat(type_params, value_params) — generic type-params (T,K,V) are not value inputs; excluded via their self-named type-expr (T : T).
2. A fn-valued parameter applied as a callee (predicate(x)) is stored as the call node's name, not a child — the marshaller now emits the atom for ExprVar reads and ExprCall callees.
3. Legitimately-irrelevant inputs (a NodeFold step's ignored edge) are declared inert via the existing _-prefix convention (node.dag step: fn(acc, _edge, sub)); the reflection skips _-prefixed params. The two such params in dependency.dag are renamed _edge (plan §4).

Proven by execution (not typecheck + grep)

claim_batch over --source-root dsl --source-root src/v2: GREEN (dead-wire count 0) → un-declare one inert param (_edge→edge) → RED (floor FAILs) → revert → GREEN. Wave-1's three witnesses and the bridge conformance test still pass.

Honest scope

Coverage is the witness's resolve closure (the floor resolves per-entry closures), same as concept_decl_facts_live today. Whole-tree widening lands with #5364's corpus-as-node accessor (ctx.modules = whole tree); this PR is its SOURCE half. The opaque Rust-seed resolve_auth realization remains the separate wave-2 perturbation witness.

🤖 Generated with Claude Code