process-gap: VP-INDEX row description not auto-synced when VP body narrows

## Symptom
VP-INDEX row descriptions duplicate prose from the VP body's Property Statement. When the VP body is narrowed (e.g., VP-076 v1.0 → v1.1 added "well-formed request" qualifier), the corresponding VP-INDEX row description retained the original "unconditionally" wording, alongside a stale EC-version anchor (e.g., "EC-007 v1.10" when the BC is now v1.12). Multiple registry-note line citations of the BC version were also stale.

Detected during fresh-context adversarial Pass 21 (lens-2) on a downstream vsdd-factory consumer.

## Root cause
Same family as the BC↔story sibling-fix gap, but at the VP↔VP-INDEX boundary. The fix-burst that narrows the VP body doesn't fan out into the index row.

## Proposed fix
- Either: VP-INDEX should programmatically derive row descriptions from VP body Property Statements (avoid duplication entirely)
- Or: codify a policy that any VP body edit triggers a VP-INDEX row sync in the same burst

The first option (derived index) eliminates the drift class. The second option (policy + checklist) is cheaper to roll out.

## Severity
LOW-MEDIUM — same shape as the BC↔story gap; tractable via spec-steward agent enforcement.