Pace candidate funnel to send capacity

docs/data-flow.md

@@ -25,7 +25,7 @@ stateDiagram-v2
 
 The discovery loop rotates through enabled subreddits and authenticated runtimes. A runtime fetches Reddit `/new` data using the process-shared `RedditRequestCoordinator`. Intake deduplicates post IDs and authors, excludes processed/contacted history, stores the full post snapshot, source type, weight, and timestamps, and logs exact intake counts.
 
-The queue has a bounded active size. Screening also pauses at configured `reddit.maxReadyCandidates`, and due delivery retries are promoted only while that ready capacity exists. Reddit request pacing, not a tight application poll, is the primary limiter.
+The queue grows to a demand-based target rather than a fixed backlog. The target is the smaller of configured `reddit.maxReadyCandidates` and the work that authenticated running accounts can still send within the recent-post window, accounting for rolling hourly capacity and minimum message spacing. Intake admits only the current deficit, pauses at zero outbound capacity, and reports fetched posts left unevaluated because the funnel is full. Reddit request pacing, not a tight application poll, remains the primary request limiter.
 
 ### 2. Screening and preparation