v3.4.1 — Fix session 'already in use' loop

Fix

When a Claude CLI session fails with "Session ID already in use" (zombie process holding the lock), the bridge retries with a fresh session. If the retry also fails, the fresh session is now invalidated from disk — preventing the next request from reusing the same poisoned UUID in a loop.

Without this fix, a single stuck session could cause every subsequent Sonnet request to fail instantly with "already in use", forcing all traffic through the fallback chain indefinitely.