Keep posts created in the same second they are ingested

[huxint]

Summary

PostStore::insert_posts uses a strict < when comparing created_at against the current wall-clock second, so a post whose create event is applied in the same second it was created is silently discarded and never enters the in-network store.

Root cause

thunder/posts/post_store.rs:134:

posts.retain(|p| {
    p.created_at < current_time
        && current_time - p.created_at <= (self.retention_seconds as i64)
});

Both timestamps are epoch seconds, so for a low-latency pipeline created_at == current_time is a normal case, not a future-dated timestamp. The event is consumed once and not revisited for the lifetime of the process — only a restart, which re-reads the topic under a fresh consumer group, would recover it — so the freshest in-network content is simply missing from that instance's store.

Fix

Use <= so only genuinely future-dated posts are rejected. Boundary arithmetic is unaffected: at equality current_time - created_at == 0, which passes the retention check here, and the u64 subtraction in trim_old_posts still cannot underflow since created_at <= current_time continues to hold at insert time.

Verification

• One-character change. thunder/ ships no Cargo manifest, so the crate cannot be compiled from this snapshot; rustfmt parses the file cleanly.
• The existing unit tests in this file only use created_at values of current_time - 1 and older, so they do not exercise this boundary and are unaffected by the change.