breedr/.zenflow/tasks/738246ea-e870-4b26-8734-d87fe75cb8a6/investigation.md

Investigation: Bug in Pairing Simulator

Bug Summary

In the Pairing Simulator page, clicking the "Simulate Pairing" button results in the following error: Unexpected token '<', "<!--DOCTYPE "... is not valid JSON

Root Cause Analysis

The frontend PairingSimulator.jsx makes a POST request to /api/pedigree/coi when simulating a pairing. However, the backend server/routes/pedigree.js does not define a /coi route. Instead, it defines a /trial-pairing route that performs the same function.

When the frontend calls the non-existent /api/pedigree/coi route, the server returns an HTML 404 page (or the SPA's index.html if in production). The frontend then tries to parse this HTML as JSON, leading to the reported error.

Additionally, PedigreeView.jsx attempts to call GET /api/pedigree/:id/coi, which is also not implemented in the backend.

Affected Components

• client/src/pages/PairingSimulator.jsx: Calls /api/pedigree/coi (POST).
• client/src/pages/PedigreeView.jsx: Calls /api/pedigree/:id/coi (GET).
• server/routes/pedigree.js: Missing route definitions for /coi and /:id/coi.

Proposed Solution

1. Update server/routes/pedigree.js to:
   • Alias POST /api/pedigree/coi to the existing trial-pairing logic.
   • Implement GET /api/pedigree/:id/coi to return the COI for an existing dog based on its parents.
2. Ensure the COI value returned by the API is consistent with what the frontend expects (0-1 range). Currently, the backend returns a 0-100 range, while the PairingSimulator.jsx expects 0-1 and multiplies by 100 in the UI.

Implementation Plan

1. Backend Changes:
   • Modify server/routes/pedigree.js to add router.post('/coi', ...) using the same logic as trial-pairing.
   • Add router.get('/:id/coi', ...) to server/routes/pedigree.js.
   • Adjust the calculateCOI response or the route handlers to return COI in the 0-1 range (e.g. 0.05 for 5%) to match PairingSimulator.jsx's expectation.
2. Frontend Cleanup:
   • Check if PedigreeView.jsx and pedigreeHelpers.js need adjustments once the backend returns the 0-1 range. formatCOI in pedigreeHelpers.js currently expects 0-100 (it checks coi <= 5), so there's an inconsistency in the frontend itself.