fix(clustering): re-title events from their cluster, not their seed article

[flvvius]

Summary

Fixes events whose title and summary describe different stories.

Root cause

An event's title is the title of whichever article created it, and nothing ever updated it as the cluster grew (clustering.ts sets title at insert("events") and never patches it). The summary, by contrast, is regenerated from every article in the cluster.

So when a cluster is seeded by one story and later dominated by another, the summary follows the majority and the title does not.

Two production examples:

Event	Cluster
"Adjuncta șefului cabinetului lui Zelenski a fost arestată"	18 articles — 17 about the CIA director's Moscow visit. The single arrest article (Biziday) seeded the event and supplied the title.
"Oana Țoiu a comentat la CNN vizita șefului CIA…"	7 articles — 6 about Nicușor Dan's Fox News editorial. One Digi24 article gave the title.

Roughly 4–6% of recent events were affected. (A naive title/summary word-overlap scan reports more, but many are false positives — the prompt mandates paraphrase, so low overlap is often correct.)

Fix

lib/eventTitle.ts picks the medoid of the cluster's article titles under token overlap: the majority story's titles score high against one another, the outlier scores near zero. In the Moscow cluster the seventeen Moscow headlines share moscova/ratcliffe/directorul; the lone arrest headline shares almost nothing and loses.

• Pure string logic — no embeddings, no model call.
• Runs inside summarization, which already holds every article, so it costs no extra reads. This matters because the attach path deliberately avoids scanning all articles (that was the perf(convex): cut prod bill from ~$41/mo to ~$1-3/mo #63 I/O work).
• Title and summary are now written in the same patch from the same inputs — the invariant that was missing.
• A rename must beat the incumbent by RETITLE_MARGIN so near-ties cannot flip a published headline back and forth as articles trickle in.

slug is deliberately not touched

It is the permanent URL and is already shared and indexed. A repaired event keeps its old slug and gains a correct title; changing slugs would break shared links, canonicals and the sitemap.

Backfill

retitleDivergentEvents repairs events already stored, which would otherwise keep a wrong headline until something happened to re-summarize them. Paginated, dryRun: true by default, returns before/after samples.

Testing

338 passed, 4 skipped across 40 files. New tests are built on the real Moscow cluster: the outlier scores lowest, the event gets renamed to a Moscow headline, a coherent cluster is left alone, small clusters never rename, and unrelated titles don't oscillate.

Also fixed two bugs in my own stopword list before shipping: a stray Cyrillic token, and china — which would have stripped a meaningful word from headlines.

🤖 Generated with Claude Code

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Generated by Claude Code

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