chore(event): smaller limits for event list api

[nickbest-ph]

Problem

The /api/projects/:id/events/ endpoint is deprecated but still serves some amount of traffic. For each request, it fetches full Person records for every distinct_id in the result set, just to extract 3 property keys (email, name, username) and a boolean (is_identified) per person.

The endpoint previously allowed up to 50,000 events per request (via ?limit=50000) and defaulted to 3,500 for CSV exports. At the fat tail this produces person lookups returning thousands of full Person records with complete properties blobs.

Changes

Cap the deprecated events list API to return at most 1,000 events per request, down from 50,000.

• QUERY_DEFAULT_EXPORT_LIMIT (CSV export default): 3,500 → 1,000
• New EVENT_LIST_MAX_LIMIT = 1_000: replaces the global MAX_SELECT_RETURNED_ROWS (50,000) as the cap for this endpoint only

This is scoped entirely to posthog/api/event.py — no other endpoints are affected.

The PostHog frontend does not call this API (it uses the HogQL events query runner instead), so this only impacts external API consumers using a deprecated endpoint.

How did you test this code?

• existing tests should cover existing behaviour
• added test to make sure we adhere to limit

Docs update

🤖 Agent context

[github-actions]

🎭 Playwright didn't run on this PR — your changes touch code that could affect E2E behavior, but Playwright is opt-in via label now to keep CI cost down.

Add the run-playwright label if you want an E2E sweep before merging — CI will pick it up automatically.

Most PRs don't need this. Real regressions still get caught on master and fix-forward.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
posthog/api/test/test_event.py:924-947
**Test doesn't actually exercise the cap**

The test creates only 1 event and then checks that `response["next"] is None`. With a single event in the DB, `next` will always be `None` regardless of whether the cap is 1,000 or 50,000 — so the assertion doesn't prove the cap is being applied. To verify enforcement, the test needs to insert more than `EVENT_LIST_MAX_LIMIT` events and assert that at most 1,000 are returned in a single response, even when `?limit=50000` is passed.

_{Reviews (1): Last reviewed commit: "adds test" | Re-trigger Greptile}

[tests-posthog]

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[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-05-26 23:52 UTC	Run
prod-us	✅ Deployed	2026-05-27 00:02 UTC	Run
prod-eu	✅ Deployed	2026-05-27 00:04 UTC	Run