Correct Dedup Cache Keys

When implementing cursor-based dedup/caching for event dispatch, ensure the dedup “key space” matches the real uniqueness of what you’re trying to prevent:

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Prompt

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When implementing cursor-based dedup/caching for event dispatch, ensure the dedup “key space” matches the real uniqueness of what you’re trying to prevent:

  • Key on the right unit of change: using a stable thread id alone can permanently suppress future events. Prefer composite keys (e.g., include event timestamp/version).
  • Record dedup after successful dispatch in every lane/path: if one lane fetches content (comments/body/trigger) but doesn’t persist its dedup keys, another lane will re-fetch and re-dispatch the same items.
  • Apply both lower and upper bounds when re-discovering triggers: after cursor eviction/trim, omitting the lower-bound (windowSince) can resurrect stale triggers.
  • Maintain cursor trims across all dedup buckets: if you trim one list but not the others, dedup correctness degrades over time.
  • Be careful with caching headers: don’t apply cacheable/read headers to transient error responses.

Practical template:

// 1) Dedup key must change when the triggering content changes.
const notifKey = `${notification.id}|${notification.updated_at}`; // not just notification.id

if (this.isDispatched(this.cursor.dispatchedNotifications, notifKey)) return;

// 2) Dispatch
await this.handleInbound(envelope);

// 3) Persist dedup keys for the exact items you dispatched
this.recordDispatched('dispatchedComments', dedupKey);
this.recordDispatched('dispatchedBodies', `${chatId}|${threadId}`);
this.recordDispatched('dispatchedEvents', triggerKey);

// 4) When re-discovering triggers, include both bounds
const event = events.findLast((candidate) => {
  const t = candidate.created_at;
  return t && t <= ctx.maxUpdatedAt && t > ctx.windowSince;
});

Acceptance checklist for reviews: 1) Every dispatch path has a corresponding, persisted dedup record (comments/bodies/events) on success. 2) Dedup keys include all dimensions needed to distinguish distinct “things to dispatch.” 3) Trigger search uses the same window bounds as the comment/body fetch logic. 4) Cursor trimming covers every dedup bucket you rely on. 5) HTTP read/caching headers are only applied on non-error response branches (or explicitly proven safe).

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