Assert durable mutation failures through verification reports #115

Problem and outcome

The 2026-09-30 audit of completed ROADMAP entries identified this obligation. Roadmap: T-21.2. Source: docs/audits/completed-roadmap-2026-09-30.md and the original task fields in ROADMAP.md on feature/roadmap-m4-tasks. Those original criteria remain authoritative.

Prove each frozen durable mutation yields the exact report variant and achieved verification depth.

Scope

Run the structural corruption corpus through durable report ingress instead of relying only on decoder assertions.

Acceptance checks

• Every required mutation maps to expected typed refusal and achieved depth through the report interface.
• expected/observed evidence is exact.
• no failed verification yields a success receipt or mutates storage.
• golden mappings and permanent regression evidence cover every required subject.

Prerequisites and relationship to existing work

Requires the durable verification-report issue created by this audit; #20 remains the tracking parent.

These are evidence-backed prerequisite proposals, not a claim that GitHub already records dependency edges. Parent grouping and shared files do not themselves imply ordering.

Exclusions

No new arbitrary mutation taxonomy or format changes.

Merge boundary and definition of done

One coherent PR delivers this observable outcome and leaves the target branch building and passing relevant checks. Preserve exact-byte identity, canonical formats, refusal precision, bounded resource use, and documented recovery. No broken intermediate mainline state is acceptable. Use the pinned Rust toolchain; run fmt, Clippy with warnings denied, and appropriate debug/release failure-mode checks. Cite concrete evidence, update the roadmap/ledger only when the original criteria are met, and retain issue → PR → integration-commit traceability. Do not treat an unmerged local change as delivered.