[Brian Krabach (bkrabach)]

Summary

Documentation-only follow-up to #444 and its non-blocking Second Opinion review.

• State the shared provider.check_available return-or-raise convention consistently. Literal False refusal is defensive behavior of the operation consumer, not a universal host convention.
• Distinguish operation preparation's abort-on-error policy from ordinary child-preference fallback through declared alternatives.
• Describe the trusted resolver boundary, nested plan mutability, provider-owned integrity/admission and current exception-taxonomy limits without claiming new enforcement.
• Remove stale pre-merge wording while retaining the experimental contract's DRAFT/unfrozen status.

Scope and trade-off

Only docs/MODEL-ROLE-CONSUMPTION.md and docs/provider-failure-policy.md change. No Core changes, runtime changes, new routing policy, dependency changes or contract freeze. This makes existing behavior explicit rather than changing already-reviewed behavior during downstream adoption.

Defensive runtime improvements and additional refusal/copy unit cases noted in the review are not represented as fixed by this documentation change.

Verification

• git diff --check passed.
• Relative document link targets checked against the repository.
• Wording checked against operation_routing.py and the existing child preference implementation.
• Runtime files are byte-identical to merged feat: add optional strategy-neutral operation routing preparation #444. No new runtime tests or model/image calls were performed for this docs-only change.

Integration

This clarification does not mean the downstream image-routing feature has shipped. Provider, bundle and host adoption remain separate changes. No deployment or automatic merge is requested.