remember_saveable with the notebook's getValue()/setValue(), over the host's rememberSaveableWrapper #102

INTENT §5.9 and SPEC S5.6 (decided 2026-10-04).

remember_saveable(initial) in pythonx.compose.runtime calls python-multiplatform-compose's @Composable rememberSaveableWrapper(init, type) (python-multiplatform #174). The type strings are bool/int/long/float/str, with bool tested before int. Any other value, or an int beyond 64 bits, is a TypeError.

It returns a thin wrapper over the Kotlin MutableState, with getValue(), setValue(v) and .value. Outside a composition it is a RuntimeError. The app attaches the state itself (App.messages = messages = remember_saveable("")), so notebook cells 9-13 work as written.

Done when tests written first (red, then green) cover the following against fake host rows shaped after the agreed wrapper:

• the type rule;
• the three spellings over one state;
• the error outside a composition;
• an @app root that attaches App.messages, read and written from outside the composition;
• the stub types.

The real-Compose save/restore proof is python-multiplatform #174.