fix: Fix cohort membership Kafka message format

[gustavohstrassburger]

Problem

The realtime cohort calculation workflow was sending Kafka messages to the cohort_membership_changed topic with snake_case field names, causing validation errors in the CDP cohort membership consumer.

The consumer expected camelCase field names (personId, cohortId, teamId, cohort_membership_changed) matching its Zod schema, but the workflow was sending snake_case names (person_id, cohort_id, team_id, status).

This resulted in validation errors:
Error: Invalid cohort membership change message:

[
    { "code": "invalid_type", "expected": "string", "received": "undefined", "path": ["personId"], "message": "Required" },
    { "code": "invalid_type", "expected": "number", "received": "undefined", "path": ["cohortId"], "message": "Required" },
    ...
]

Changes

Updated consumer schema to use snake_case (cdp-cohort-membership.consumer.ts):
Updated workflow to produce snake_case messages (realtime_cohort_calculation_workflow.py)

How did you test this code?

• Manually

[Copilot]

Pull request overview

This PR fixes a critical bug in the realtime cohort calculation workflow that was sending Kafka messages with incorrect field names to the cohort_membership_changed topic. The consumer expected camelCase field names matching its Zod schema validation, but the workflow was sending snake_case names, causing validation errors.

Key Changes:

• Updated Kafka message payload format in the realtime cohort workflow to use camelCase field names (teamId, cohortId, personId, cohort_membership_changed) instead of snake_case
• Removed the unused last_updated field from the payload
• Increased kafka_ui HTTP request header size limit to fix UI loading issues

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
posthog/temporal/messaging/realtime_cohort_calculation_workflow.py	Fixed Kafka message payload format to match consumer schema expectations by converting field names to camelCase and renaming status to cohort_membership_changed
docker-compose.dev.yml	Added environment variable to increase kafka_ui HTTP request header size limit

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