chore(clickhouse): sanity-check ai_events convergence gate (expected fail)

[orian]

Problem

Deliberate negative test of the merged convergence gate (#67134, #67281): prove the multinode smoke fails when a migration drifts a managed cluster from its HCL golden.

Changes

• Migration 0285 adds a column to sharded_ai_events on NodeRole.AI_EVENTS, with no matching posthog/clickhouse/hcl/ change.

Expected outcome: ci-clickhouse-multinode-migrations fails at the check_live_hcl step with DRIFT: local/ai_events … ALTER table posthog.sharded_ai_events. Not for merge — will be closed.

How did you test this code?

I'm an agent. Reproduced locally against the running multinode stack via the pinned hclexp container: with the ALTER applied, check-live (enforcing) reports the single sharded_ai_events drift and exits non-zero; ops stays clean. This PR is to confirm the same failure in real CI.

🤖 Agent context

Autonomy: Human-driven (agent-assisted). Sanity check requested to validate the enforcing gate end to end. Migration-only; to be closed once CI shows red.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "chore(clickhouse): sanity-check ai_event..." | Re-trigger Greptile}

[greptile-apps]

The file is missing a trailing newline after the update. The previous value (0284_message_assets) had one, and most text files in the repo follow the same convention — some tooling also expects it.

Suggested change

	0285_ai_events_gate_drift_check
	0285_ai_events_gate_drift_check

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[github-actions]

ClickHouse migration SQL per cloud environment

• unset
  • all

    ALTER TABLE sharded_ai_events ADD COLUMN IF NOT EXISTS gate_drift_sanity_check UInt8 DEFAULT 0

• US, EU, DEV
  • ai_events

    ALTER TABLE sharded_ai_events ADD COLUMN IF NOT EXISTS gate_drift_sanity_check UInt8 DEFAULT 0

[orian]

Sanity check complete ✅ — the multinode smoke failed exactly as intended: migration 0285 altered sharded_ai_events with no HCL change, and the convergence gate caught it (DRIFT: local/ai_events … ALTER table posthog.sharded_ai_events, stage check_live_hcl, exit 1). Closing — this was only to validate the enforcing gate.