The corpus's numeric-recursion example and poster child for the
recursion-bound family: route/ and calc/ recurse over a data shape,
fibonacci recurses over a number. A .ckh/.ck regular-module pair plus
an app and config, modelled on calc/.

- Fib.ckh/Fib.ck: two total, pure u64 functions -- naive `fib` (the
  exponential self-cycle) and `fib_linear` (tail-recursive `fib_acc`,
  linear depth). First corpus module whose fns carry no effect row and
  no `or` error surface. Depth annotation omitted while its spelling is
  open, as route/ and calc/ do.
- Main.ck: entry actor logs one number per definition; pure tests pin
  the base cases, fib(10)=55, and (via a turbofish-bounded literal
  iterated with for-in) that both definitions agree.
- trap.md: three E0301s in Main.ck for unresolved stdlib `Show`, the
  same gap counter/ and calc/ trap; Fib.ck/Fib.ckh parse clean.

Corpus harness reconciles green both ways.

@@ -0,0 +211,4 @@
+/// pushing any diagnostic into `diags`. The body is located by `FnId` through
+/// `bodies_by_fn`; a decl the resolver never bound (no scope entry, no body, no
+/// lifted signature) is skipped — it was already diagnosed upstream.
+#[allow(clippy::too_many_arguments)] // mirrors `check_fn_body`'s own irreducible input set: the decl, its source, scope, resolved bodies, the project tables, the interner, and the diagnostic sink.

@@ -0,0 +118,4 @@
+        .arg("--stdlib")
+        .arg(&stdlib)
+        .status()
+        .expect("spawn the `ckc` binary")