design(connections): retain local data when an unlinked relay was the last route #362

What: An unlinked relay-only saved environment needs an explicit route and local-data lifecycle.
Why: Removing the last route currently deletes the environment, cache and drafts, so #292 retains relay-only entries on account-list disappearance.
So what: Track this bounded follow-up separately from #292's automatic relay-learning implementation, per the user's round-2 rule.

Outcome and acceptance

Represent the unusable last relay honestly without silently deleting local data; any destructive action is explicit. Decide product behavior before implementation.

Evidence and required proof

Verified Registry.removeLocked clears cache/owned data; routesAfterRemoving returns no routes for relay-only and relay-dependent direct entries.
Source base: 503282b. Add focused behavioral proof for the acceptance before delivering a future fix.
Design/review record: #292 (comment).

Non-goals and blockers

No provisioning, authentication weakening, primary-environment change or implementation in the current #292 task. Last-route destructive behavior requires a product decision.

Contribution to the Objective

Reliable remote route state keeps the Promachos and Drafters reachable across machines.

Requirements and who asked: The user requires non-core findings from #292 round 2 onward to become linked follow-up Issues.
Deleted: Expanding the automatic membership PR with this separate behavior.
Bottleneck: Resolve the acceptance in this follow-up without widening #292.
Checked myself: Verified Registry.removeLocked clears cache/owned data; routesAfterRemoving returns no routes for relay-only and relay-dependent direct entries.