Sentry Error Contract Epochs

Tracker reference: pm-h75tjh.

The release reliability gate declares 2026.8.7 as the minimum producer version for canonical pm.error_code and pm.exit_code tags. An unresolved event with a known older release is reported as legacy_pre_contract; it does not block a current release merely because it cannot satisfy a future producer contract.

Events from the minimum producer or newer remain blocking when they are unexpected faults or lack the required tags. Events with no parseable producer version are also blocking. JSON output includes the minimum version, legacy_pre_contract_total, bounded legacy ids, and a bounded blocking-reason row for each current issue. Expected handled usage, not-found, and conflict errors remain a separate non-blocking class.

This epoch rule only changes gate classification. It does not resolve, delete, or hide Sentry issues, and it does not weaken fatal or error thresholds for current producers.