attempt-3 pinned current_source_file to the metaprogram's defining module
across the whole body lowering (lowerComptimeCall / monomorphizePackFn). That
pin also covered caller-provided comptime $-arg nodes spliced into the body by
substituteComptimeNodes — but those are CALLER-authored and must resolve in the
caller's visibility context, not the callee's. Result: a caller-owned helper
passed to an imported metaprogram errored "'<name>' is not visible".
Fix: stamp each comptime $-arg node with the caller's source_file at the cpn
build site (stampCallerSource, in lowerComptimeCall + monomorphizePackFn);
lowerExpr switches current_source_file to a node's source_file when present, so
the substituted subtree resolves against the caller while the surrounding callee
code keeps the defining-module pin. No exemption / fall-open.
Regression: examples/0738-modules-comptime-arg-caller-context.sx — a caller-owned
helper passed as a comptime-ONLY $-arg through a namespaced import. Fail-before
(attempt-3 binary): "'caller_name' is not visible". Pass-after: prints
"hello world", exit 0. Comptime-only, so it does not exercise issue 0107.
0106 RESOLVED banner extended (point 3: body=defining context, substituted
$-args=caller context). run_examples 473 -> 474; zig build test 412/412.
8875a28641