bug(orchestration): deduplicate pending reads beyond freshness TTL #925

Expected behavior

In-flight deduplication lasts until settlement/invalidation; completed-value freshness begins at settlement. Scope/generation changes must prevent joining or publishing stale reads.

Source finding and impact

CachedValue combines promise with expiresAt initialized at request creation. The 250ms expiry/prune path removes unresolved reads while one global renderer request slot remains busy, allowing identical polls to enqueue duplicate work.

Evidence and environment

Inspected source at 552914f5610518458f944fa1bdaf63f243685bd1 on 2026-09-12 in the local macOS workspace. This finding has not yet been reproduced through a running application or the package integration suite.

• src/main/orchestration/OrchestrationBridge.ts

Regression and acceptance

Hold the first renderer read beyond several freshness periods and repeatedly poll the same key; one admitted read remains. Mutation invalidation admits a new-generation read and late old output cannot refill current cache. Measure queue age and pending-key count without claiming a benchmark speedup.

The resolving PR must protect the observable contract and document any remaining uncertainty. This planning pass makes no runtime changes.

Refs #918; planning finding F12.