X_UPGRADE_INSTALL_FAILED
Means
bun install failed after x upgrade wrote the pins
Typical cause
bun install exited non-zero: a package that no longer exists at the target version, a peer conflict, or the network. The pins and Bun floor are written and uncommitted
Fix
git restore . — undoes the pins, since the tree was clean; then fix what the cause names and re-run: x upgrade --json