fix(ai): default series type to event in funnel report tool

[nielskaspers]

Summary

• Adds a z.preprocess wrapper around the zChartEventItem discriminated union to default type to "event" when the field is missing
• Prevents Zod invalid_union_discriminator errors when the LLM omits the type field in series objects during AI chat funnel report generation

Issue

Fixes #327

Changes

• packages/validation/src/index.ts: Wrapped zChartEventItem with z.preprocess() that adds type: "event" to objects missing the type field before discriminated union validation

Testing

• Ask the AI chat to generate a funnel report
• Verify the tool call succeeds even if the LLM omits type in series objects
• Verify that explicitly passing type: "event" or type: "formula" still works as before

Summary by CodeRabbit

• Bug Fixes
  • Enhanced chart event validation to automatically handle inputs without explicit type specifications, reducing validation errors and improving data compatibility for chart operations.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b0c124a0-863f-4761-80ef-a87e3b3c9b00

📥 Commits

Reviewing files that changed from the base of the PR and between a1ce71f and a06a2f1.

📒 Files selected for processing (1)

• packages/validation/src/index.ts

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📝 Walkthrough

Walkthrough

Modified the zChartEventItem schema to automatically inject the missing type: 'event' discriminator field during preprocessing when the field is absent from incoming objects, enabling validation of incomplete event item payloads.

Changes

Cohort / File(s)	Summary
Validation Schema Preprocessing packages/validation/src/index.ts	Added preprocessing wrapper to zChartEventItem that auto-injects type: 'event' for objects missing the discriminator field before passing to discriminated union validation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A little injection of type, so swift,
When 'event' goes missing, we give it a gift,
No more validation wails and sighs—
The AI chat now soars through the skies! 🚀✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: defaulting the series type to 'event' in the funnel report tool via the z.preprocess wrapper applied to zChartEventItem.
Linked Issues check	✅ Passed	The PR implements the third suggested fix from issue #327 by adding a z.preprocess wrapper that defaults missing 'type' to 'event' before validation, directly addressing the LLM omission problem.
Out of Scope Changes check	✅ Passed	All changes are scoped to the zChartEventItem schema modification, directly implementing the proposed default fallback fix without introducing unrelated alterations.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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