Resuming sessions from v2.1.89 in v2.1.90 causes excessive token usage (no prompt caching)

Description

When resuming a conversation session that was originally started in Claude Code v2.1.89, the upgraded v2.1.90 client does not properly cache the existing context. This causes the full conversation to be re-sent without prompt caching on the next message, resulting in significantly higher token consumption.

Steps to reproduce

1. Start a session in Claude Code v2.1.89 with a large context (multiple files open, long conversation)
2. Upgrade to v2.1.90
3. Resume the same session and send a message
4. Observe significantly higher token usage compared to a fresh session

Expected behavior

Resumed sessions should benefit from prompt caching regardless of which version originally created them.

Actual behavior

The full conversation context is sent without caching, consuming excessive tokens on the first message after resuming.

Environment

• Claude Code v2.1.89 → v2.1.90
• Linux (Ubuntu/WSL)

Notes

It appears v2.1.90 already includes caching fixes, but they don't apply retroactively to sessions created in v2.1.89. A migration or cache invalidation step during version upgrade might help.