[mstan]

Consumer regeneration exposed two problems in the framework test step:

• On Windows, CREATE_NO_WINDOW can leave the test child without usable inherited console handles, hiding all diagnostics. Forward the caller’s stdout and stderr explicitly.
• Scaffolder fixtures inherit SNESRECOMP_ROOT from the consumer build. The missing-submodule test then legitimately generates through that external checkout and fails its expected repair-hint assertion. Clear the inherited override in scaffold fixtures; cases that need a framework already provide one explicitly.

Validation on native Windows:

• Both real child-process output tests failed before the stream fix and pass afterward, covering success and failure status.
• The missing-submodule failure was reproduced with the consumer’s checkout override; all focused scaffold/output tests now pass: 31 passed, 1 skipped, with that override still set in the parent.
• The separate runtime review bundle passes 856 tests, 2 skipped in the normal standalone environment.

This changes test execution and fixture isolation only; no generated code or built runtime changes. Tracking: beads-h6si.