XO1303: module version not in the cache while offline

With XO_OFFLINE=1 or --offline, the toolchain never touches the network: every required module version must already be in the module cache ($XO_MODCACHE, default <user cache dir>/xo/mod) or in the main module’s vendor/. This version is in neither. Fetch it once while online (xo mod tidy, xo get <path>@<version>, or any build), or commit a vendor/ directory with xo vendor. See core 4.2 and decision 0086.

Example

XO_OFFLINE=1 xo build .   # billing v1.4.0 was never fetched

Fix

xo mod tidy               # online, once
XO_OFFLINE=1 xo build .   # from the cache from now on

Run xo explain XO1303 for this text in a terminal, or see section 10.6 of the specification.