Rename the per-file opt-in from `__cwa__` to `from __future__ import __obs__`
(internal StrictCWA becomes StrictOBS).
OBS type model:
- `Box[T]` / `BoxT[T]` is one owned indirection (`Ptr(T)`); a user generic
class named Box keeps precedence.
- `RawT[T]` is the unboxed value type; primitives, arrays and pointers stay raw.
- `Option[T]` is the explicit spelling of the existing `T?` suffix
(parser marker renamed to OptionT; NullableT still accepted) and resolves
to a nullable pointer.
- Declaration annotations (locals, globals, parameters, returns) get an
`AutoBoxT[...]` wrapper in OBS files before the vpi pass, so struct/class
types become `Box[T]` while primitives stay raw; struct field declarations
are left untouched, preserving the layout (`U.__sizeof__()` stays 16).
Explicit `Box[...]`/`RawT[...]`/`Option[...]`/`T?` are not wrapped again.
Ownership:
- an OBS move (`b: T = a` where `a` owns a heap object) marks the source
slot as released, so later uses (including `a.field`) fail fast; rebinding
clears the state.
LSP: `Box`, `RawT` and `Option` are offered as builtin completions.
Probe: `_U: U = new U(1,2,3,4); _B: U = _U; print(U.__sizeof__())` prints 16 and
`print(_U.a)` fails with LifetimeError; Box[U]/Option[U]/U? declarations work;
`Box[U] = None` is rejected; `__cwa__` is rejected and `__obs__` accepted.
Self-host 110/110; ListTest, GenericTest, GenericTest3, GenericTest4,
PtrOpProbe, HashLibTest, NewTest, NewLifetimeTest, StructTest and
EscapeOkTest pass.
TermiNexus
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