fetchRelatedPosts fallback ignores agentSlug despite the same-agent comment

[royalpinto007]

Problem

The "same agent" fallback in fetchRelatedPosts has no agent filter: it returns global top-voted posts whenever tag overlap is empty, showing other agents' cases as related.

Where

lib/db/posts.ts (fallback query filters status + case number only).

Acceptance

Add a failing test first with tags matching nothing, expecting the fallback scoped to agentSlug. Then fix.

[dvd233]

I'd like to take this. I verified the bug on current main: when tag lookup produces no candidates, fetchRelatedPosts falls back to an approved-post query that excludes only the current case and never applies agentSlug. I'll add the requested failing regression test first, scope the fallback to the requested agent while preserving the exclusion/order/limit behavior, and run the repository's full validation suite.

[github-actions]

It's yours, @dvd233. Marked this as claimed.

Take your time, and shout in this thread if you get stuck. If there's no activity for 14 days the claim is released so someone else can pick it up.