[linkdata]

Summary

• Make a missing intermediate JsVar parent raise the same JaWS path error as a missing direct parent.
• Document that dotted store bindings need their parent objects on window before jaws.js runs; startup still fails fast if the precondition is unmet.
• Add a browser-client regression test for shallow and deep missing parents plus a valid path.

Verification

• Regression test failed before the fix with a raw TypeError for a.b.c and passes after the fix.
• JAWS_REQUIRE_NODE=1 go test -race ./...
• JAWS_REQUIRE_NODE=1 go test ./...
• go vet ./...
• node --check lib/assets/jaws.js

Fixes #431