Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.
checkCallArity compares the supplied count against the declared params
(min = params without trailing defaults, max = params.len, unbounded
past a variadic) at the five plain dispatch sites in lowerCall — bare
selected-author + lazy, namespace alias-gate + qualified, struct
method, ufcs. Pack / comptime / generic / #compiler / #builtin callees
keep their own dispatch. The method/ufcs sites also gain the
appendDefaultArgs fill the generic-instance leg already had, so
trailing defaults work on dot-calls instead of emitting under-arity
calls. lowerStmt's local fn_decl arm now registers a pointer into the
AST node in fn_ast_map, not a stack temporary that aliased every later
local fn.
