Env-var-only seam (§3.2), zero logic change (diff is one added
condition): the version-check `git fetch` at :215 now skips when
SESSION_START_OFFLINE is set (non-empty), leaving _remote_ver empty
(same as any other offline/fetch-failure path already handled) instead
of hitting the network.
Unlocks (BACKLOG, not built here): a HOME-injected truth-table + smoke
test for session-start.sh (J4-14), without every run paying a network
round-trip or depending on origin/main being reachable.
Verified: bash -n clean, shellcheck clean (pre-existing SC1091 info
only, unrelated). Behavioral: SESSION_START_OFFLINE=1 runs in ~15ms
(no fetch) vs ~740ms unset (fetch attempted) — identical banner output
either way (v4.0.0 == CONFIG_VERSION, no update line in both). Full
`make test` exit 0.
Bastien Chanot
f2948df639