Claude ignores existing working code and rewrites from scratch, breaking what worked

Severity: HIGH — Regression / Working features destroyed

What happened

A fully-functional production map application had working features: hotel name callouts, price markers, venue chips, event carousel, booking URLs, mobile-responsive layout. Claude was asked to add theme color options.

Instead of adding color themes as CSS variable overrides, Claude rewrote significant portions of both app.js and app.css, removing or breaking:

• Hotel name label callouts (symbol layer that floated above price circles)
• Price marker logic (hotels with no price showed "?" instead of being hidden)
• The sidebar layout and fonts
• Booking URL format (reverted to broken /hotels/{liteapi_id} format)

The user had to spend an entire session re-debugging features that were already working before Claude touched them.

Impact

• Multiple working features broken simultaneously
• Hours of lost work re-implementing what was already there
• Live production site degraded while user debugged Claude's regressions

Expected behavior

When asked to add a cosmetic feature (color themes), Claude should make the minimal change required — add CSS custom property overrides — without touching unrelated working logic.

Requested resolution

• Refund of session credits spent re-debugging regressions Claude introduced
• Bonus API credits for the stress and lost productivity
• Fix: Claude should default to minimal-change implementations, especially for cosmetic requests on working production code