FLOOR REPAIR: in-flight shared fill is charged as marginal until store — repair the classification boundary (design first, characterization is landed in docs/plans/required-floor-in-flight-shared-fill-findings.md)

[gunbai-bot]

Summary

• Keep the existing CPU safety clock and ceiling unchanged; this PR raises no limit and grants no pre-publication fill credit.
• When that unchanged ceiling fires, emit typed, located FillBudgetExceeded only if subtracting the active prospective fill brings marginal claim CPU back within the limit. Otherwise retain ordinary EvaluationBudgetExceeded.
• Preserve store-only fill accounting and nested stored-descendant netting while exposing a stable fill-budget-exceeded cause token.
• Record the design and clarify that AlreadyPresent is servable, not a publication refusal.

This is an attribution repair and measurement instrument, not an availability exemption. A prospective fill over the limit still stops. Counting these refusals can provide evidence for a future separately modeled fill envelope; this PR creates no such policy.

The budget expression at the poll is only opened to retain the raw CPU sample needed for attribution: it remains exactly thread_cpu_nanos() - shared_artifact_fill_cpu_nanos(), the existing budgeted_cpu_nanos() clock.

Discriminating evidence

The regression pair changes exactly one fact: resolved-identity admission. Both arms run the same compiled producer through the real evaluator under the same 5ms ceiling, and both cross it. The unadmitted arm retains EvaluationBudgetExceeded; admitting that exact producer produces FillBudgetExceeded naming it.

Test plan

• cargo check -p v1-compiler — passed remotely.
• cargo test -p v1-compiler --lib admitted_in_flight_fill_crossing_is_typed_and_unadmitted_control_is_ordinary -- --nocapture — passed remotely.
• cargo fmt --all --check — passed in commit/push hooks.

Worker attestation

• Title describes the change.
• Body summarizes what and why.
• Tests and outcomes are named above.
• All commits on this branch are intentional.
• No secrets, credentials, or large binaries are included.