The exec argv is words

An argv the shell renders is total; an argv crossing into execve(2) is words. The shapes that are not words are declared in exactly one place, and that one declaration is read at both moments a call can be refused — by the checker before the run, by the spawn at it.

Total inside, gated at the operating-system call. The asymmetry is not an oversight in either direction:

• Inside the shell, Value::render_argv (core/src/types/value.rs) gives every value a text form, so a base frame, a handler arm and the audit trail take every shape. echo [a: 1] prints a map; echo $f prints a block.
• At the boundary, an argument is one word, and a list (several arguments), a map or record (fields), a block or lambda or native (a computation not yet run), a handle (still running), and bytes (a channel) are not words. Unit is the word () and a tagged value renders, so neither is refused.

One declaration, two readings. RefusedArg (core/src/types/exec_arg.rs) names those shapes, with of_value for the spawn (runtime::command::vet), of_ty for the checker’s argv rule (typecheck::infer), and one remedy per shape so a user meeting either refusal meets one language. Both maps are wildcard-free: a new Value or Ty constructor has to be given a verdict on both sides before it compiles. A second statement of the set is the failure mode this rule exists to prevent — drift between them is invisible until a user meets one refusal and not the other.

Concrete types only, and no spread. The checker refuses an argument whose resolved type is one of those shapes (T0057) and says nothing about a type variable; and it never refuses a spread, whose element count is dynamic — an empty spread contributes no argument, so refusing it would reject a call that spawns cleanly. What the type does not say, the spawn still does (R0001). The static gate is therefore pure gain: no program that ran before stops running (exec-boundary-gated-statically).

This is a hard rule, not a stylistic preference. Do not make the in-shell rendering partial, do not gate an in-shell argv, do not refuse on a type variable or on a spread’s elements, and do not state the refused set a second time — extend RefusedArg and let both sides read it.

See argv-is-a-list-of-strings for why an argv is List String inside and bytes at the call, and fixed-arity for the argv/application split the boundary sits on.