0707 — Export validation checks only export compatibility

Context

Supersedes [0706]. Export validation repeated constructor checks and indexed output names from families already rejected. That added bookkeeping and omitted healthy families for collisions that could not reach the output.

Decision

• Core constructors own kind/unit validity and built-in declaration identity; the custom producer owns the raw vulkan. namespace restriction. Do not repeat these checks in the adapter. This change adds no new write checks.
• Keep export-specific checks: family-wide kind/unit consistency, translated attribute-key ambiguity, translation failures, and reserved output names. Retained measurements still cannot supply collection-health gauges.
• Translate each eligible family once. Check name collisions only among families that passed their own export checks; reject all participants in a remaining collision, independent of row order.
• Keep [0706]‘s collection-local read-health and rejection gauges, logging, error behavior, pinned translation strategy, and reader contract unchanged.

Consequences

A rejected family remains logged and counted but no longer blocks an otherwise healthy family from exporting. The adapter trusts core measurement validity; it is not a backstop for measurements mutated after construction or written outside the intended producers. No cache or persistent rejection state is added.