# Add D-093: v0 usage grade system design decision · versecafe/strata

[View on GitCafe](https://git.cafe/versecafe/strata/commit/596445afea8642bb9f8858aaae0e14a0d2d30061)

Repository: [versecafe/strata](https://git.cafe/versecafe/strata)

Visibility: public

Requested revision: 596445afea8642bb9f8858aaae0e14a0d2d30061

Requested commit: 596445afea8642bb9f8858aaae0e14a0d2d30061

Commit: 596445afea8642bb9f8858aaae0e14a0d2d30061

Tree: 4209aae8d09ad2ed71c573ec86d4573af51c56ad

Author: versecafe

Committer: versecafe

## Message

```
Add D-093: v0 usage grade system design decision

D-024's {0,1,ω} semiring and D-011's phase modalities are pure spec —
zero code representation anywhere. The one piece of surface syntax
that already reaches toward this space, ghost fn/ghost let, already
parses but is completely inert downstream: strata-hir discards
ghost-ness when naming a function, and lower_block has no arm for
GhostStmt, so a ghost let falls to StatementKind::Unsupported and
isn't represented in HIR at all.

v0 finishes exactly that: grade 0 ("erased, compile-time-only, no
runtime witness") becomes real, checked via a second one-bit taint
pass structurally identical to the existing mem_tainted/
reject_if_tainted mechanism, rejecting a grade-0 value at any
hardware-sink boundary. Grades attach only to let bindings and whole
functions — the only two forms that already parse — not parameters,
not struct fields, not reg/mem.

Grade 1, phase modalities beyond the grade-0/ghost overlap the spec
already asserts, and typestate-over-linearity are all deferred whole,
not partially scoped: grade 1 needs genuinely new context-splitting
checker infrastructure (no extension of the taint pass), typestate is
structurally downstream of grade 1 per D-026's own text, and phase
modalities are a different axis (classification, not usage-count)
with no forcing fixture.

OP-7's ω-promotion soundness concern is not reached by grade-0-only
scope — no binding in v0 is ever grade 1 — but FIX-ω is recorded as a
hard obligation that must ship atomically with any future
grade-1-inside-feedback support, not as a follow-up, per this
project's standing enforce-properly-or-don't-ship posture for
foundational judgment work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

```

## Parents

- [7a7a1544c70f936a726ff076a85218064160dee5](https://git.cafe/versecafe/strata/commit/7a7a1544c70f936a726ff076a85218064160dee5?format=markdown)

[Source at this commit](https://git.cafe/versecafe/strata/tree/596445afea8642bb9f8858aaae0e14a0d2d30061?format=markdown)