How the dispatcher treats tokens that look like flags but aren’t in the
allowlist. unknown controls flag-shaped unknowns; numeric_dash opts
into -NUMBER shorthand (e.g. head -20).
Predicate over the first positional token of a fallback grammar.
Lets a TOML-declared fallback say “the first positional must look
like a path” without the handler hardcoding the test.
Whether unrecognized flag-shaped tokens are denied or silently accepted
as positional arguments. The default (Strict) makes the allowlist
authoritative — any unrecognized -X or --foo is denied.
Heuristic for “this token looks like a file path.” Used by the
pathPositionalShape. Conservative on purpose — a bare word
like Tiltfile is a valid filename in cwd but the heuristic
rejects it to avoid swallowing flag-less subcommands. Callers
that want bare-name acceptance should match a sub block instead.