Bug report: PostHog AI reports success creating insights when API actually returned validation errors

Bug Description

Please describe.

Max AI attempted to create multiple insights for a user, initially reported a problem creating the insights, but later said they exist and gave the user insight names and links to insights that are not found. It looks like the insights were never actually created.

I noticed the insight payloads look to be missing the required query wrapper. The AI was sending:

{
  "kind": "TrendsQuery",
  "series": [...],
  ...
}

But the API expects:

{
  "query": {
    "kind": "TrendsQuery",
    "series": [...],
    ...
  }
}

This resulted in a PydanticOutputParserException with "Field required" at location ["query"]. From cd524f8a-3a7e-4476-ac2c-bb082496810b:

"PydanticOutputParserException: [{\"type\":\"missing\",\"loc\":[\"query\"],\"msg\":\"Field required\",\"input\":{\"kind\":\"TrendsQuery\",\"series\":[{\"kind\":\"EventsNode\",\"event\":\"$exception\",\"math\":\"total\",\"properties\":[{\"type\":\"event\",\"key\":\"$pathname\",\"operator\":\"exact\",\"value\":\"/signup\"}]}],\"dateRange\":{\"date_from\":\"-30d\",\"date_to\":null},\"interval\":\"day\",\"trendsFilter\":{\"display\":\"ActionsLineGraph\",\"showLegend\":false,\"showValuesOnSeries\":false,\"yAxisScaleType\":\"linear\",\"aggregationAxisFormat\":\"numeric\"},\"filterTestAccounts\":true}}], occurred at:\n```\n{\"kind\": \"TrendsQuery\", \"series\": [{\"kind\": \"EventsNode\", \"event\": \"$exception\", \"math\": \"total\", \"properties\": [{\"type\": \"event\", \"key\": \"$pathname\", \"operator\": \"exact\", \"value\": \"/signup\"}]}], \"dateRange\": {\"date_from\": \"-30d\", \"date_to\": null}, \"interval\": \"day\", \"trendsFilter\": {\"display\": \"ActionsLineGraph\", \"showLegend\": false, \"showValuesOnSeries\": false, \"yAxisScaleType\": \"linear\", \"aggregationAxisFormat\": \"numeric\"}, \"filterTestAccounts\": true}\n```"

Session Traces: https://us.posthog.com/project/2/llm-analytics/sessions/0d83044a-0c16-4653-be88-bdf2ef9e3efe?date_from=-24h

How to reproduce

1. Ask Max to create one or more insights (e.g., "Create a trends insight showing $exception events on /signup over the last 30 days")
2. Look for the insights that were "created", note the insights don't exist
3. Check trace to see Pydantic validation error

Additional context

From: https://posthoghelp.zendesk.com/agent/tickets/46578 (moved to PostHog: https://us.posthog.com/project/2/support/tickets/49129)

Debug info

Session: https://us.posthog.com/project/sTMFPsFhdP1Ssg/replay/019b9eb3-e1ec-7ac7-8b06-6227238e6b06?t=849
Admin: http://go/adminOrgUS/019aea12-cc53-0000-3f9b-d486307dd1e1 (project ID 260343)

Start by tracing Max's insight-creation request from the reproduction scenario through the API response and validation-error handling. Compare the payload shape with the required query wrapper, then verify that failed creations are not reported as successful. Add or update coverage for the Pydantic validation-error case and run the relevant tests once the entry point is located.